Abstract:

The air–sea exchange and oceanic cycling of greenhouse gases (GHG), including carbon dioxide (CO₂), nitrous oxide (N₂O), methane (CH₄), carbon monoxide (CO), and nitrogen oxides (NO_x = NO + NO₂), are fundamental in controlling the evolution of the Earth’s atmospheric chemistry and climate. Significant advances have been made over the last 10 years in understanding, instrumentation and methods, as well as deciphering the production and consumption pathways of GHG in the upper ocean (including the surface and subsurface ocean down to approximately 1000 m). The global ocean under current conditions is now well established as a major sink for CO₂, a major source for N₂O and a minor source for both CH₄ and CO. The importance of the ocean as a sink or source of NO_x is largely unknown so far. There are still considerable uncertainties about the processes and their major drivers controlling the distributions of N₂O, CH₄, CO, and NO_x in the upper ocean. Without having a fundamental understanding of oceanic GHG production and consumption pathways, our knowledge about the effects of ongoing major oceanic changes—warming, acidification, deoxygenation, and eutrophication—on the oceanic cycling and air–sea exchange of GHG remains rudimentary at best. We suggest that only through a comprehensive, coordinated, and interdisciplinary approach that includes data collection by global observation networks as well as joint process studies can the necessary data be generated to (1) identify the relevant microbial and phytoplankton communities, (2) quantify the rates of ocean GHG production and consumption pathways, (3) comprehend their major drivers, and (4) decipher economic and cultural implications of mitigation solutions.

Abstract:

In the northern Gulf of Mexico shelf, the Mississippi-Atchafalaya River System (MARS) impacts the carbonate system by delivering freshwater with a distinct seasonal pattern in both total alkalinity (Alk) and dissolved inorganic carbon (DIC), and promoting biologically driven changes in DIC through nutrient inputs. However, how and to what degree these processes modulate the interannual variability in calcium carbonate solubility have been poorly documented. Here, we use an ocean-biogeochemical model to investigate the impact of MARS's discharge and chemistry on interannual anomalies of aragonite saturation state (Ω_Ar). Based on model results, we show that the enhanced mixing of riverine waters with a low buffer capacity (low Alk-to-DIC ratio) during high-discharge winters promotes a significant Ω_Ar decline over the inner-shelf. We also show that increased nutrient runoff and vertical stratification during high-discharge summers promotes strong negative anomalies in bottom Ω_Ar, and less intense but significant positive anomalies in surface Ω_Ar. Therefore, increased MARS discharge promotes an increased frequency of suboptimal Ω_Ar levels for nearshore coastal calcifying species. Additional sensitivity experiments further show that reductions in the Alk-to-DIC ratio and nitrate concentration from the MARS significantly modify the simulated interannual Ω_Ar patterns, weakening the positive surface Ω_Ar anomalies during high-discharge summers or even producing negative surface Ω_Ar anomalies. Our findings suggest that riverine water carbonate chemistry is a main driver of interannual variability in Ω_Ar over river dominated ocean margins.

Abstract:

The years since 2000 have been a golden age in in situ ocean observing with the proliferation and organization of autonomous platforms such as surface drogued buoys and subsurface Argo profiling floats augmenting ship-based observations. Global time series of mean sea surface temperature and ocean heat content are routinely calculated based on data from these platforms, enhancing our understanding of the ocean’s role in the Earth’s climate system. Individual measurements of meteorological, sea surface and subsurface variables directly improve our understanding of the Earth System, weather forecasting, and climate projections. They also provide the data necessary for validating and calibrating satellite observations. Maintaining this ocean observing system has been a technological, logistical, and funding challenge. The global COVID-19 pandemic, which took hold in 2020, added strain to the maintenance of the observing system. A survey of the contributing components of the observing system illustrates the impacts of the pandemic from January 2020 through December 2021. The pandemic did not reduce the short-term geographic coverage (days to months) capabilities mainly due to the continuation of autonomous platform observations. In contrast, the pandemic caused critical loss to longer-term (years to decades) observations, greatly impairing the monitoring of such crucial variables as ocean carbon and the state of the deep ocean. So, while the observing system has held under the stress of the pandemic, work must be done to restore the interrupted replenishment of the autonomous components and plan for more resilient methods to support components of the system that rely on cruise-based measurements.

Abstract:

This contribution to the RECCAP2 (REgional Carbon Cycle Assessment and Processes) assessment analyzes the processes that determine the global ocean carbon sink, and its trends and variability over the period 1985-2018, using a combination of models and observation-based products. The mean sea-air CO₂ flux from 1985-2018 is -1.6±0.2 PgC yr^-1 based on an ensemble of reconstructions of the history of sea surface pCO₂ (pCO₂ products). Models indicate that the dominant component of this flux is the net oceanic uptake of anthropogenic CO₂, which is estimated at -2.1±0.3 PgC yr^-1 by an ensemble of ocean biogeochemical models, and -2.4±0.1 PgC yr^-1 by two ocean circulation inverse models. The ocean also degasses about 0.65±0.3 PgC yr^-1 of terrestrially-derived CO₂, but this process is not fully resolved by any of the models used here. From 2001-2018, the pCO₂ products reconstruct a trend in the ocean carbon sink of -0.61±0.12 PgC yr^-1 decade^-1, while biogeochemical models and inverse models diagnose an anthropogenic CO₂-driven trend of -0.34±0.06 and -0.41±0.03 PgC yr^-1 decade^-1, respectively. This implies a climate-forced acceleration of the ocean carbon sink in recent decades, but there are still large uncertainties on the magnitude and cause of this trend. The interannual to decadal variability of the global carbon sink is mainly driven by climate variability, with the climate-driven variability exceeding the CO₂-forced variability by 2-3 times. These results suggest that anthropogenic CO₂ dominates the ocean CO₂ sink, while climate-driven variability is potentially large but highly uncertain and not consistently captured across different methods.

Abstract:

The chemistry of the global ocean is rapidly changing due to the uptake of anthropogenic carbon dioxide (CO₂). This process, commonly referred to as ocean acidification (OA), is negatively impacting many marine species and ecosystems. In this study, we combine observations in the global surface ocean collected by NOAA Pacific Marine Environmental Laboratory and Atlantic Oceanographic and Meteorological Laboratory scientists and their national and international colleagues over the last several decades, along with model outputs, to provide a high-resolution, regionally varying view of global surface ocean carbon dioxide fugacity, carbonate ion content, total hydrogen ion content, pH on total scale, and aragonite and calcite saturation states on selected time intervals from 1961 to 2020. We discuss the major roles played by air-sea anthropogenic CO₂ uptake, warming, local upwelling processes, and declining buffer capacity in controlling the spatial and temporal variability of these parameters. These changes are occurring rapidly in regions that would normally be considered OA refugia, thus threatening the protection that these regions provide for stocks of sensitive species and increasing the potential for expanding biological impacts.

Abstract:

Accurate assessment of anthropogenic carbon dioxide (CO₂) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate is critical to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe and synthesize data sets and methodology to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO₂ emissions (E_FOS) are based on energy statistics and cement production data, while emissions from land-use change (E_LUC), mainly deforestation, are based on land-use and land-use change data and bookkeeping models. Atmospheric CO₂ concentration is measured directly, and its growth rate (G_ATM) is computed from the annual changes in concentration. The ocean CO₂ sink (S_OCEAN) is estimated with global ocean biogeochemistry models and observation-based fCO₂ products. The terrestrial CO₂ sink (S_LAND) is estimated with dynamic global vegetation models. Additional lines of evidence on land and ocean sinks are provided by atmospheric inversions, atmospheric oxygen measurements, and Earth system models. The resulting carbon budget imbalance (B_IM), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of imperfect data and incomplete understanding of the contemporary carbon cycle. All uncertainties are reported as ±1σ. For the year 2022, E_FOS increased by 0.9% relative to 2021, with fossil emissions at 9.9±0.5 Gt C yr⁻¹ (10.2±0.5 Gt C yr⁻¹ when the cement carbonation sink is not included), and E_LUC was 1.2±0.7 Gt C yr⁻¹, for a total anthropogenic CO₂ emission (including the cement carbonation sink) of 11.1±0.8 Gt C yr⁻¹ (40.7±3.2 Gt CO₂ yr⁻¹). Also, for 2022, G_ATM was 4.6±0.2 Gt C yr⁻¹ (2.18±0.1 ppm yr⁻¹; ppm denotes parts per million), S_OCEAN was 2.8±0.4 Gt C yr⁻¹, and S_LAND was 3.8±0.8 Gt C yr⁻¹, with a B_IM of −0.1 Gt C yr⁻¹ (i.e., total estimated sources marginally too low or sinks marginally too high). The global atmospheric CO₂ concentration averaged over 2022 reached 417.1±0.1 ppm. Preliminary data for 2023 suggest an increase in E_FOS relative to 2022 of +1.1% (0.0 % to 2.1%) globally and atmospheric CO₂ concentration reaching 419.3 ppm, 51% above the pre-industrial level (around 278 ppm in 1750). Overall, the mean of and trend in the components of the global carbon budget are consistently estimated over the period 1959–2022, with a near-zero overall budget imbalance, although discrepancies of up to around 1 Gt C yr⁻¹ persist for the representation of annual to semi-decadal variability in CO₂ fluxes. Comparison of estimates from multiple approaches and observations shows the following: (1) a persistent large uncertainty in the estimate of land-use changes emissions, (2) a low agreement between the different methods on the magnitude of the land CO₂ flux in the northern extra-tropics, and (3) a discrepancy between the different methods on the strength of the ocean sink over the last decade. This living-data update documents changes in methods and data sets applied to this most recent global carbon budget as well as evolving community understanding of the global carbon cycle.

Abstract:

Accurately predicting future ocean acidification (OA) conditions is crucial for advancing OA research at regional and global scales, and guiding society's mitigation and adaptation efforts. This study presents a new model-data fusion product covering 10 global surface OA indicators based on 14 Earth System Models (ESMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6), along with three recent observational ocean carbon data products. The indicators include fugacity of carbon dioxide, pH on total scale, total hydrogen ion content, free hydrogen ion content, carbonate ion content, aragonite saturation state, calcite saturation state, Revelle Factor, total dissolved inorganic carbon content, and total alkalinity content. The evolution of these OA indicators is presented on a global surface ocean 1° × 1° grid as decadal averages every 10 years from preindustrial conditions (1750), through historical conditions (1850–2010), and to five future Shared Socioeconomic Pathways (2020–2100): SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5. These OA trajectories represent an improvement over previous OA data products with respect to data quantity, spatial and temporal coverage, diversity of the underlying data and model simulations, and the provided SSPs. The generated data product offers a state-of-the-art research and management tool for the 21st century under the combined stressors of global climate change and ocean acidification. The gridded data product is available in NetCDF at the National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Information: https://www.ncei.noaa.gov/data/oceans/ncei/ocads/metadata/0259391.html, and global maps of these indicators are available in jpeg at https://www.ncei.noaa.gov/access/ocean-carbon-acidification-data-system/synthesis/surface-oa-indicators.html.

Abstract:

The oceanic uptake and resulting storage of the anthropogenic CO₂ (C_ant) that humans have emitted into the atmosphere moderates climate change. Yet our knowledge about how this uptake and storage has progressed in time remained limited. Here, we determine decadal trends in the storage of C_ant by applying the eMLR(C*) regression method to ocean interior observations collected repeatedly since the 1990s. We find that the global ocean storage of C_ant grew from 1994 to 2004 by 29 ± 3 Pg C dec⁻¹ and from 2004 to 2014 by 27 ± 3 Pg C dec⁻¹ (±1σ). The storage change in the second decade is about 15 ± 11% lower than one would expect from the first decade and assuming proportional increase with atmospheric CO₂. We attribute this reduction in sensitivity to a decrease of the ocean buffer capacity and changes in ocean circulation. In the Atlantic Ocean, the maximum storage rate shifted from the Northern to the Southern Hemisphere, plausibly caused by a weaker formation rate of North Atlantic Deep Waters and an intensified ventilation of mode and intermediate waters in the Southern Hemisphere. Our estimates of the C_ant accumulation differ from cumulative net air-sea flux estimates by several Pg C dec⁻¹, suggesting a substantial and variable, but uncertain net loss of natural carbon from the ocean. Our findings indicate a considerable vulnerability of the ocean carbon sink to climate variability and change.

Abstract:

No abstract.

Abstract:

Measuring plankton and associated variables as part of ocean time-series stations has the potential to revolutionize our understanding of ocean biology and ecology and their ties to ocean biogeochemistry. It will open temporal scales (e.g., resolving diel cycles) not typically sampled as a function of depth. In this review we motivate the addition of biological measurements to time-series sites by detailing science questions they could help address, reviewing existing technology that could be deployed, and providing examples of time-series sites already deploying some of those technologies. We consider here the opportunities that exist through global coordination within the OceanSITES network for long-term (climate) time series station in the open ocean. Especially with respect to data management, global solutions are needed as these are critical to maximize the utility of such data. We conclude by providing recommendations for an implementation plan.

Abstract:

No abstract.

Abstract:

Accurate assessment of anthropogenic carbon dioxide (CO₂) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate is critical to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe and synthesize data sets and methodologies to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO₂ emissions (E_FOS) are based on energy statistics and cement production data, while emissions from land-use change (E_LUC), mainly deforestation, are based on land use and land-use change data and bookkeeping models. Atmospheric CO₂ concentration is measured directly, and its growth rate (G_ATM) is computed from the annual changes in concentration. The ocean CO₂ sink (S_OCEAN) is estimated with global ocean biogeochemistry models and observation-based data products. The terrestrial CO₂ sink (S_LAND) is estimated with dynamic global vegetation models. The resulting carbon budget imbalance (B_IM), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of imperfect data and understanding of the contemporary carbon cycle. All uncertainties are reported as ±1σ. For the year 2021, E_FOS increased by 5.1% relative to 2020, with fossil emissions at 10.1 ± 0.5 GtC yr⁻¹ (9.9 ± 0.5 GtC yr⁻¹ when the cement carbonation sink is included), and E_LUC was 1.1 ± 0.7 GtC yr⁻¹, for a total anthropogenic CO₂ emission (including the cement carbonation sink) of 10.9 ± 0.8 GtC yr⁻¹ (40.0 ± 2.9 GtCO₂). Also, for 2021, G_ATM was 5.2 ± 0.2 GtC yr⁻¹ (2.5 ± 0.1 ppm yr⁻¹), S_OCEAN was 2.9  ± 0.4 GtC yr⁻¹, and S_LAND was 3.5 ± 0.9 GtC yr⁻¹, with a B_IM of −0.6 GtC yr⁻¹ (i.e. the total estimated sources were too low or sinks were too high). The global atmospheric CO₂ concentration averaged over 2021 reached 414.71 ± 0.1 ppm. Preliminary data for 2022 suggest an increase in E_FOS relative to 2021 of +1.0% (0.1% to 1.9%) globally and atmospheric CO₂ concentration reaching 417.2 ppm, more than 50% above pre-industrial levels (around 278 ppm). Overall, the mean and trend in the components of the global carbon budget are consistently estimated over the period 1959–2021, but discrepancies of up to 1 GtC yr⁻¹ persist for the representation of annual to semi-decadal variability in CO₂ fluxes. Comparison of estimates from multiple approaches and observations shows (1) a persistent large uncertainty in the estimate of land-use change emissions, (2) a low agreement between the different methods on the magnitude of the land CO₂ flux in the northern extratropics, and (3) a discrepancy between the different methods on the strength of the ocean sink over the last decade. This living data update documents changes in the methods and data sets used in this new global carbon budget and the progress in understanding of the global carbon cycle compared with previous publications of this data set. The data presented in this work are available at https://doi.org/10.18160/GCP-2022 (Friedlingstein et al., 2022b).

Abstract:

Accurate assessment of anthropogenic carbon dioxide (CO₂) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate is critical to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe and synthesize datasets and methodology to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO₂ emissions (EFOS) are based on energy statistics and cement production data, while emissions from land-use change (ELUC), mainly deforestation, are based on land use and land-use change data and bookkeeping models. Atmospheric CO₂ concentration is measured directly, and its growth rate (GATM) is computed from the annual changes in concentration. The ocean CO₂ sink (SOCEAN) is estimated with global ocean biogeochemistry models and observation-based data products. The terrestrial CO₂ sink (SLAND) is estimated with dynamic global vegetation models. The resulting carbon budget imbalance (BIM), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of imperfect data and understanding of the contemporary carbon cycle. All uncertainties are reported as ±1σ . For the first time, an approach is shown to reconcile the difference in our ELUC estimate with the one from national greenhouse gas inventories, supporting the assessment of collective countries’ climate progress. For the year 2020, EFOS declined by 5.4% relative to 2019, with fossil emissions at 9.5 ± 0.5 GtC yr⁻¹ (9.3 ± 0.5 GtC yr⁻¹ when the cement carbonation sink is included), and ELUC was 0.9 ± 0.7 GtC yr⁻¹, for a total anthropogenic CO₂ emission of 10.2 ± 0.8 GtC yr⁻¹ (37.4 ± 2.9 GtCO₂). Also, for 2020, GATM was 5.0 ± 0.2 GtC yr⁻¹ (2.4 ± 0.1 ppm yr⁻¹), SOCEAN was 3.0 ± 0.4 GtC yr⁻¹, and SLAND was 2.9 ± 1 GtC yr⁻¹, with a BIM of −0.8 GtC yr⁻¹. The global atmospheric CO₂ concentration averaged over 2020 reached 412.45 ± 0.1 ppm. Preliminary data for 2021 suggest a rebound in EFOS relative to 2020 of +4.8% (4.2% to 5.4%) globally. Overall, the mean and trend in the components of the global carbon budget are consistently estimated over the period 1959–2020, but discrepancies of up to 1 GtC yr⁻¹ persist for the representation of annual to semi-decadal variability in CO₂ fluxes. Comparison of estimates from multiple approaches and observations shows (1) a persistent large uncertainty in the estimate of land-use changes emissions, (2) a low agreement between the different methods on the magnitude of the land CO₂ flux in the northern extra-tropics, and (3) a discrepancy between the different methods on the strength of the ocean sink over the last decade. This living data update documents changes in the methods and datasets used in this new global carbon budget and the progress in understanding of the global carbon cycle compared with previous publications of this dataset (Friedlingstein et al., 2020, 2019; Le Quéré et al., 2018b,a, 2016, 2015b,a, 2014, 2013). The data presented in this work are available at https://doi.org/10.18160/gcp-2021 (Friedlingstein et al., 2021).

Abstract:

Effective data management plays a key role in oceanographic research as cruise-based data, collected from different laboratories and expeditions, are commonly compiled to investigate regional to global oceanographic processes. Here we describe new and updated best practice data standards for discrete chemical oceanographic observations, specifically those dealing with column header abbreviations, quality control flags, missing value indicators, and standardized calculation of certain properties. These data standards have been developed with the goals of improving the current practices of the scientific community and promoting their international usage. These guidelines are intended to standardize data files for data sharing and submission into permanent archives. They will facilitate future quality control and synthesis efforts and lead to better data interpretation. In turn, this will promote research in ocean biogeochemistry, such as studies of carbon cycling and ocean acidification, on regional to global scales. These best practice standards are not mandatory. Agencies, institutes, universities, or research vessels can continue using different data standards if it is important for them to maintain historical consistency. However, it is hoped that they will be adopted as widely as possible to facilitate consistency and to achieve the goals stated above.

Abstract:

The key processes driving the air–sea CO₂ fluxes in the western tropical Atlantic (WTA) in winter are poorly known. WTA is a highly dynamic oceanic region, expected to have a dominant role in the variability in CO₂ air–sea fluxes. In early 2020 (February), this region was the site of a large in situ survey and studied in wider context through satellite measurements. The North Brazil Current (NBC) flows northward along the coast of South America, retroflects close to 8°N and pinches off the world’s largest eddies, the NBC rings. The rings are formed to the north of the Amazon River mouth when freshwater discharge is still significant in winter (a time period of relatively low run-off). We show that in February 2020, the region (5–16°N, 50–59°W) is a CO₂ sink from the atmosphere to the ocean (−1.7 Tg C per month), a factor of 10 greater than previously estimated. The spatial distribution of CO₂ fugacity is strongly influenced by eddies south of 12°N. During the campaign, a nutrient-rich freshwater plume from the Amazon River is entrained by a ring from the shelf up to 12°N leading to high phytoplankton concentration and significant carbon drawdown (∼20 % of the total sink). In trapping equatorial waters, NBC rings are a small source of CO₂. The less variable North Atlantic subtropical water extends from 12°N northward and represents ∼60 % of the total sink due to the lower temperature associated with winter cooling and strong winds. Our results, in identifying the key processes influencing the air–sea CO₂ flux in the WTA, highlight the role of eddy interactions with the Amazon River plume. It sheds light on how a lack of data impeded a correct assessment of the flux in the past, as well as on the necessity of taking into account features at meso- and small scales

Abstract:

Assessing the status of ocean acidification across ocean and coastal waters requires standardized procedures at all levels of data collection, dissemination, and analysis. Standardized procedures for assuring quality and accessibility of ocean carbonate chemistry data are largely established, but a common set of best practices for ocean acidification trend analysis is needed to enable global time series comparisons, establish accurate records of change, and communicate the current status of ocean acidification within and outside the scientific community. Here we expand upon several published trend analysis techniques and package them into a set of best practices for assessing trends of ocean acidification time series. These best practices are best suited for time series capable of characterizing seasonal variability, typically those with sub-seasonal (ideally monthly or more frequent) data collection. Given ocean carbonate chemistry time series tend to be sparse and discontinuous, additional research is necessary to further advance these best practices to better address uncharacterized variability that can result from data discontinuities. This package of best practices and the associated open-source software for computing and reporting trends is aimed at helping expand the community of practice in ocean acidification trend analysis. A broad community of practice testing these and new techniques across different data sets will result in improvements and expansion of these best practices in the future.

Abstract:

The fugacity or partial pressure of CO₂ in surface water (fCO_2w) is a key parameter to determine air-sea CO₂ fluxes and the evolution of ocean acidification. Despite its importance some key physical chemical characteristics are not fully resolved, notably its dependence on temperature. The fCO_2w is mostly measured by autonomous underway systems near in situ sea surface temperature (SST). Subsurface measurements are commonly carried out on individual (discrete) samples at a fixed temperature, normally 20 °C. Here, the underway system observations are compared with co-located discrete observations to determine the consistency of these types of measurements. The co-located discrete fCO_2w at 20 °C and underway fCO_2w measurements at SST are used to infer the temperature dependence of CO₂. In addition, calculated fCO_2w from total alkalinity (TA) and total dissolved inorganic carbon (DIC) are compared with the underway and discrete fCO_2w measurements. For 21 cruises spanning the major ocean basins from 1992 to 2020 a temperature dependence of 4.13 ± 0.01% °C⁻¹ is determined in close agreement with a widely used previous empirical estimate of 4.23 ± 0.02% °C⁻¹ for North Atlantic surface water. The temperature dependency of calculated fCO_2w from TA and DIC using recommended constants is 4.10% °C⁻¹ for 17 cruises where there are co-located measurements of fCO_2w, TA and DIC.

Abstract:

Ocean heat and carbon are transported through the Florida Straits, contributing to the Atlantic Meridional Overturning Circulation, and playing an important role in climate. Insufficient observations of carbonate chemistry within the Florida Straits have limited our understanding of ocean acidification within this region. To examine carbonate chemistry and carbon transport dynamics within this region, we developed an algorithm to estimate dissolved inorganic carbon (DIC) using more routinely measured input parameters (temperature, salinity, and dissolved oxygen [DO]) and the corresponding sampling date, depth, and longitude. The developed DIC algorithm output demonstrates good agreement with limited existing in situ observations. By applying this algorithm, we developed a seasonally resolved time series of DIC spanning from 2002 to 2018 for the Florida Straits at 27°N. This time series suggests that short-term variations in surface water DO and DIC were strongly influenced by the Florida Current transport. The long-term increase in DIC was mainly caused by anthropogenic carbon accumulation and DO decrease. The highest increasing rate in DIC was found in North Atlantic Central Water where DO decrease was fastest while the decreasing rate in pH was highest in Antarctic Intermediate Water (AAIW) because of the lower buffer capacity of this water mass. The long-term pH decrease, especially in AAIW, can impact the health of deep corals in the Florida Straits. Quantifying carbon transport between the coast of Florida and the Bahamas is important to understanding the carbonate chemistry dynamics and the long-term acidification of this important region.

Abstract:

Knowledge of the ocean carbon cycle is critical in light of its role in sequestering CO₂ from the atmosphere and for meeting goals and targets such as the UN Framework Convention on Climate Change (UNFCCC) Paris Agreement, the UN 2030 Agenda for Sustainable Development, and the associated UN Decade of Ocean Science for Sustainable Development. Increasing levels of CO₂ in the ocean, predominantly due to human greenhouse gas emissions, and the partitioning of CO₂ into organic and inorganic species have fundamental impacts on ocean carbon cycling and ecosystem health. The Integrated Ocean Carbon Research (IOC-R) effort aims to address key issues in ocean carbon research through investigative and observational goals. It takes advantage of the appreciable knowledge gained from studies over the last four decades of the ocean carbon cycle and its perturbations. IOC-R addresses the clear and urgent need to better understand and quantify the ocean carbon cycle in an integrative fashion in light of the rapid changes that are currently occurring and will occur in the near future.

Abstract:

The ocean absorbs approximately a quarter of the carbon dioxide currently released to the atmosphere by human activities (C_anth). A disproportionately large fraction accumulates in the North Atlantic due to the combined effects of transport by the Atlantic Meridional Overturning Circulation (AMOC) and air–sea exchange. However, discrepancies exist between modelled and observed estimates of the air–sea exchange due to unresolved ocean transport variability. Here we quantify the strength and variability of C_anth transports across 26.5° N in the North Atlantic between 2004 and 2012 using circulation measurements from the RAPID mooring array and hydrographic observations. Over this period, decreasing circulation strength tended to decrease northward C_anth transport, while increasing C_anth concentrations (preferentially in the upper limb of the overturning circulation) tended to increase northward C_anth transport. These two processes compensated each other over the 8.5-year period. While ocean transport and air–sea C_anth fluxes are approximately equal in magnitude, the increasing accumulation rate of C_anth in the North Atlantic combined with a stable ocean transport supply means we infer a growing contribution from air–sea C_anth fluxes over the period. North Atlantic C_anth accumulation is thus sensitive to AMOC strength, but growing atmospheric C_anth uptake continues to significantly impact C_anth transports.

Abstract:

We introduce three new Empirical Seawater Property Estimation Routines (ESPERs) capable of predicting seawater phosphate, nitrate, silicate, oxygen, total titration seawater alkalinity, total hydrogen scale pH (pH_T), and total dissolved inorganic carbon (DIC) from up to 16 combinations of seawater property measurements. The routines generate estimates from neural networks (ESPER_NN), locally interpolated regressions (ESPER_LIR), or both (ESPER_Mixed). They require a salinity value and coordinate information, and benefit from additional seawater measurements if available. These routines are intended for seawater property measurement quality control and quality assessment, generating estimates for calculations that require approximate values, original science, and producing biogeochemical property context from a data set. Relative to earlier LIR routines, the updates expand their functionality, including new estimated properties and combinations of predictors, a larger training data product including new cruises from the 2020 Global Data Analysis Project data product release, and the implementation of a first-principles approach for quantifying the impacts of anthropogenic carbon on DIC and pH_T. We show that the new routines perform at least as well as existing routines, and, in some cases, outperform existing approaches, even when limited to the same training data. Given that additional training data has been incorporated into these updated routines, these updates should be considered an improvement over earlier versions. The routines are intended for all ocean depths for the interval from 1980 to ~2030 c.e., and we caution against using the routines to directly quantify surface ocean seasonality or make more distant predictions of DIC or pH_T.

Abstract:

No abstract.

Abstract:

Ocean acidification (OA) progression is affected by multiple factors, such as ocean warming, biological production, and river runoff. Here we used an ocean-biogeochemical model to assess the impact of river runoff and climate variability on the spatiotemporal patterns of OA in the Gulf of Mexico (GoM) during 1981–2014. The model showed the expected pH and aragonite saturation state (Ω_Ar) decline, due to the increase in anthropogenic carbon, with trends close to values reported for the Subtropical North Atlantic. However, significant departures from the basin-averaged pattern were obtained in part of the northern GoM shelf, where pH and Ω_Ar increased. Model sensitivity analyses showed that OA progression was counteracted by enhanced alkalinity from the Mississippi-Atchafalaya River System. Our findings highlight that river alkalinity is a key driver of carbon system variability in river-dominated ocean margins and emphasize the need to quantify riverine chemistry to properly assess acidification in coastal waters.

Abstract:

In this paper, we outline the need for a coordinated international effort toward the building of an open-access Global Ocean Oxygen Database and ATlas (GO₂DAT) complying with the FAIR principles (Findable, Accessible, Interoperable, and Reusable). GO₂DAT will combine data from the coastal and open ocean, as measured by the chemical Winkler titration method or by sensors (e.g., optodes, electrodes) from Eulerian and Lagrangian platforms (e.g., ships, moorings, profiling floats, gliders, ships of opportunities, marine mammals, cabled observatories). GO₂DAT will further adopt a community-agreed, fully documented metadata format and a consistent quality control (QC) procedure and quality flagging (QF) system. GO₂DAT will serve to support the development of advanced data analysis and biogeochemical models for improving our mapping, understanding and forecasting capabilities for ocean O₂ changes and deoxygenation trends. It will offer the opportunity to develop quality-controlled data synthesis products with unprecedented spatial (vertical and horizontal) and temporal (sub-seasonal to multi-decadal) resolution. These products will support model assessment, improvement and evaluation as well as the development of climate and ocean health indicators. They will further support the decision-making processes associated with the emerging blue economy, the conservation of marine resources and their associated ecosystem services and the development of management tools required by a diverse community of users (e.g., environmental agencies, aquaculture, and fishing sectors). A better knowledge base of the spatial and temporal variations of marine O₂ will improve our understanding of the ocean O₂ budget, and allow better quantification of the Earth’s carbon and heat budgets. With the ever-increasing need to protect and sustainably manage ocean services, GO₂DAT will allow scientists to fully harness the increasing volumes of O₂ data already delivered by the expanding global ocean observing system and enable smooth incorporation of much higher quantities of data from autonomous platforms in the open ocean and coastal areas into comprehensive data products in the years to come. This paper aims at engaging the community (e.g., scientists, data managers, policy makers, service users) toward the development of GO₂DAT within the framework of the UN Global Ocean Oxygen Decade (GOOD) program recently endorsed by IOC-UNESCO. A roadmap toward GO₂DAT is proposed highlighting the efforts needed (e.g., in terms of human resources).

Abstract:

Seawater total alkalinity (TA) is one important determinant used to monitor the ocean carbon cycle, whose spatial distributions have previously been characterized along the United States East Coast via discrete bottle samples. Using these data, several regional models for TA retrievals based on practical salinity (S) have been developed. Broad-scale seasonal or interannual variations, however, are not well resolved in these models and existing data are highly seasonally biased. This study reports findings from the first long duration deployment of a new, commercially available TA titrator aboard a research vessel and the continuous underway surface TA measurements produced. The instrument, operated on seven East Coast USA cruises during six months in 2017 and for two months in 2018 on the summertime East Coast Ocean Acidification survey (ECOA-2), collected a total of nearly 11,000 surface TA measurements. Data from these efforts, along with a newly synthesized set of more than 11,000 regional surface TA observations, are analyzed to re-examine distributions of TA and S along the United States East Coast. Overall, regional distributions of S and TA generally agreed with prior findings, but linear TA:S regressions varied markedly over time and deviated from previously developed models. This variability is likely due to a combination of biological, seasonal, and episodic influences and indicates that substantial errors of ±10–20 μmol kg⁻¹ in TA estimation from S can be expected due to these factors. This finding has likely implications for numerical ecosystem modeling and inorganic carbon system calculations. New results presented in this paper provide refined surface TA:S relationships, present more data in space and time, and improve TA modeling uncertainty.

Abstract:

Internally consistent, quality-controlled (QC) data products play an important role in promoting regional-to-global research efforts to understand societal vulnerabilities to ocean acidification (OA). However, there are currently no such data products for the coastal ocean, where most of the OA-susceptible commercial and recreational fisheries and aquaculture industries are located. In this collaborative effort, we compiled, quality-controlled, and synthesized 2 decades of discrete measurements of inorganic carbon system parameters, oxygen, and nutrient chemistry data from the North American continental shelves to generate a data product called the Coastal Ocean Data Analysis Product in North America (CODAP-NA). There are few deep-water (> 1500 m) sampling locations in the current data product. As a result, crossover analyses, which rely on comparisons between measurements on different cruises in the stable deep ocean, could not form the basis for cruise-to-cruise adjustments. For this reason, care was taken in the selection of data sets to include in this initial release of CODAP-NA, and only data sets from laboratories with known quality assurance practices were included. New consistency checks and outlier detections were used to QC the data. Future releases of this CODAP-NA product will use this core data product as the basis for cruise-to-cruise comparisons. We worked closely with the investigators who collected and measured these data during the QC process. This version (v2021) of the CODAP-NA is comprised of 3391 oceanographic profiles from 61 research cruises covering all continental shelves of North America, from Alaska to Mexico in the west and from Canada to the Caribbean in the east. Data for 14 variables (temperature; salinity; dissolved oxygen content; dissolved inorganic carbon content; total alkalinity; pH on total scale; carbonate ion content; fugacity of carbon dioxide; and substance contents of silicate, phosphate, nitrate, nitrite, nitrate plus nitrite, and ammonium) have been subjected to extensive QC. CODAP-NA is available as a merged data product (Excel, CSV, MATLAB, and NetCDF; https://doi.org/10.25921/531n-c230, https://www.ncei.noaa.gov/data/oceans/ncei/ocads/metadata/0219960.html, last access: 15 May 2021) (Jiang et al., 2021a). The original cruise data have also been updated with data providers' consent and summarized in a table with links to NOAA's National Centers for Environmental Information (NCEI) archives (https://www.ncei.noaa.gov/access/ocean-acidification-data-stewardship-oads/synthesis/NAcruises.html).

Abstract:

The Global Ocean Data Analysis Project (GLODAP) is a synthesis effort providing regular compilations of surface-to-bottom ocean biogeochemical bottle data, with an emphasis on seawater inorganic carbon chemistry and related variables determined through chemical analysis of seawater samples. GLODAPv2.2021 is an update of the previous version, GLODAPv2.2020 (Olsen et al., 2020). The major changes are as follows: data from 43 new cruises were added, data coverage was extended until 2020, all data with missing temperatures were removed, and a digital object identifier (DOI) was included for each cruise in the product files. In addition, a number of minor corrections to GLODAPv2.2020 data were performed. GLODAPv2.2021 includes measurements from more than 1.3 million water samples from the global oceans collected on 989 cruises. The data for the 12 GLODAP core variables (salinity, oxygen, nitrate, silicate, phosphate, dissolved inorganic carbon, total alkalinity, pH, CFC-11, CFC-12, CFC-113, and CCl₄) have undergone extensive quality control with a focus on systematic evaluation of bias. The data are available in two formats: (i) as submitted by the data originator but updated to World Ocean Circulation Experiment (WOCE) exchange format and (ii) as a merged data product with adjustments applied to minimize bias. For this annual update, adjustments for the 43 new cruises were derived by comparing those data with the data from the 946 quality-controlled cruises in the GLODAPv2.2020 data product using crossover analysis. Comparisons to estimates of nutrients and ocean CO₂ chemistry based on empirical algorithms provided additional context for adjustment decisions in this version. The adjustments are intended to remove potential biases from errors related to measurement, calibration, and data handling practices without removing known or likely time trends or variations in the variables evaluated. The compiled and adjusted data product is believed to be consistent with to better than 0.005 in salinity, 1% in oxygen, 2% in nitrate, 2% in silicate, 2% in phosphate, 4 µmol kg⁻¹ in dissolved inorganic carbon, 4 µmol kg⁻¹ in total alkalinity, 0.01–0.02 in pH (depending on region), and 5% in the halogenated transient tracers. The other variables included in the compilation, such as isotopic tracers and discrete CO₂ fugacity (fCO₂), were not subjected to bias comparison or adjustments. The original data, their documentation, and DOI codes are available at the Ocean Carbon Data System of NOAA NCEI (https://www.ncei.noaa.gov/access/ocean-carbon-data-system/oceans/GLODAPv2_2021/, last access: 7 July 2021). This site also provides access to the merged data product, which is provided as a single global file and as four regional ones – the Arctic, Atlantic, Indian, and Pacific oceans – under https://doi.org/10.25921/ttgq-n825 (Lauvset et al., 2021). These bias-adjusted product files also include significant ancillary and approximated data and can be accessed via https://www.glodap.info (last access: 29 June 2021). These were obtained by interpolation of, or calculation from, measured data. This living data update documents the GLODAPv2.2021 methods and provides a broad overview of the secondary quality control procedures and results.

Abstract:

The ocean is mitigating global warming by absorbing large amounts of excess carbon dioxide from human activities. To quantify and monitor the ocean carbon sink, we need a state-of-the-art data resource that makes data submission and retrieval machine-compatible and efficient.

Abstract:

Syntheses of carbonate chemistry spatial patterns are important for predicting ocean acidification impacts, but are lacking in coastal oceans. Here, we show that along the North American Atlantic and Gulf coasts the meridional distributions of dissolved inorganic carbon (DIC) and carbonate mineral saturation state (Ω) are controlled by partial equilibrium with the atmosphere resulting in relatively low DIC and high Ω in warm southern waters and the opposite in cold northern waters. However, pH and the partial pressure of CO₂ (pCO₂) do not exhibit a simple spatial pattern and are controlled by local physical and net biological processes which impede equilibrium with the atmosphere. Along the Pacific coast, upwelling brings subsurface waters with low Ω and pH to the surface where net biological production works to raise their values. Different temperature sensitivities of carbonate properties and different timescales of influencing processes lead to contrasting property distributions within and among margins.

Abstract:

No abstract.

Abstract:

Accurate assessment of anthropogenic carbon dioxide (CO₂) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate – the “global carbon budget” – is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe and synthesize data sets and methodology to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO₂ emissions (E_FOS) are based on energy statistics and cement production data, while emissions from land-use change (E_LUC), mainly deforestation, are based on land use and land-use change data and bookkeeping models. Atmospheric CO₂ concentration is measured directly and its growth rate (G_ATM) is computed from the annual changes in concentration. The ocean CO₂ sink (S_OCEAN) and terrestrial CO₂ sink (S_LAND) are estimated with global process models constrained by observations. The resulting carbon budget imbalance (B_IM), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of imperfect data and understanding of the contemporary carbon cycle. All uncertainties are reported as ±1σ. For the last decade available (2010–2019), E_FOS was 9.6 ± 0.5 GtC yr⁻¹ excluding the cement carbonation sink (9.4 ± 0.5 GtC yr⁻¹ when the cement carbonation sink is included), and E_LUC was 1.6 ± 0.7 GtC yr⁻¹. For the same decade, G_ATM was 5.1 ± 0.02 GtC yr⁻¹ (2.4 ± 0.01 ppm yr⁻¹), S_OCEAN 2.5 ±  0.6 GtC yr⁻¹, and S_LAND 3.4 ± 0.9 GtC yr⁻¹, with a budget imbalance B_IM of −0.1 GtC yr⁻¹ indicating a near balance between estimated sources and sinks over the last decade. For the year 2019 alone, the growth in E_FOS was only about 0.1 % with fossil emissions increasing to 9.9 ± 0.5 GtC yr⁻¹ excluding the cement carbonation sink (9.7 ± 0.5 GtC yr⁻¹ when cement carbonation sink is included), and E_LUC was 1.8 ± 0.7 GtC yr⁻¹, for total anthropogenic CO₂ emissions of 11.5 ± 0.9 GtC yr⁻¹ (42.2 ± 3.3 GtCO₂). Also for 2019, G_ATM was 5.4 ± 0.2 GtC yr⁻¹ (2.5 ± 0.1 ppm yr⁻¹), S_OCEAN was 2.6 ± 0.6 GtC yr⁻¹, and S_LAND was 3.1 ± 1.2 GtC yr⁻¹, with a B_IM of 0.3 GtC. The global atmospheric CO₂ concentration reached 409.85 ± 0.1 ppm averaged over 2019. Preliminary data for 2020, accounting for the COVID-19-induced changes in emissions, suggest a decrease in E_FOS relative to 2019 of about −7 % (median estimate) based on individual estimates from four studies of −6 %, −7 %, −7 % (−3 % to −11 %), and −13 %. Overall, the mean and trend in the components of the global carbon budget are consistently estimated over the period 1959–2019, but discrepancies of up to 1 GtC yr⁻¹ persist for the representation of semi-decadal variability in CO₂ fluxes. Comparison of estimates from diverse approaches and observations shows (1) no consensus in the mean and trend in land-use change emissions over the last decade, (2) a persistent low agreement between the different methods on the magnitude of the land CO₂ flux in the northern extra-tropics, and (3) an apparent discrepancy between the different methods for the ocean sink outside the tropics, particularly in the Southern Ocean. This living data update documents changes in the methods and data sets used in this new global carbon budget and the progress in understanding of the global carbon cycle compared with previous publications of this data set (Friedlingstein et al., 2019; Le Quéré et al., 2018b, a, 2016, 2015b, a, 2014, 2013). The data presented in this work are available at https://doi.org/10.18160/gcp-2020 (Friedlingstein et al., 2020)..

Abstract:

Uncertainties in carbon chemistry variability still remain large in the Gulf of Mexico (GoM), as data gaps limit our ability to infer basin-wide patterns. Here we configure and validate a regional high-resolution ocean biogeochemical model for the GoM to describe seasonal patterns in surface pressure of CO₂ (pCO₂), aragonite saturation state (ΩAr), and sea–air CO₂ flux. Model results indicate that seasonal changes in surface pCO₂ are strongly controlled by temperature across most of the GoM basin, except in the vicinity of the Mississippi–Atchafalaya river system delta, where runoff largely controls dissolved inorganic carbon (DIC) and total alkalinity (TA) changes. Our model results also show that seasonal patterns of surface ΩAr are driven by seasonal changes in DIC and TA, and reinforced by the seasonal changes in temperature. Simulated sea–air CO₂fluxes are consistent with previous observation-based estimates that show CO₂ uptake during winter–spring, and CO₂ outgassing during summer–fall. Annually, our model indicates a basin-wide mean CO2 uptake of 0.35 mol m⁻² yr⁻¹, and a northern GoM shelf (< 200 m) uptake of 0.93 mol m⁻² yr⁻¹. The observation and model-derived patterns of surface pCO₂ and CO₂ fluxes show good correspondence; thus, this study contributes to improved constraints of the carbon budget in the region.

Abstract:

Abundant and diverse cold-water coral and fish communities can be found in the deep waters of the Florida Straits, which are believed to be living under suboptimal conditions impacted by increasing oceanic CO₂ levels. Yet, little is known regarding the spatial–temporal variability of bottom carbonate chemistry parameters and their dynamic drivers in this area. To address this issue, we present results from numerical simulations of a coupled physical-biogeochemical model for the south Florida shelf and Florida Straits. Our exploratory analysis focuses on two well-known deep-coral habitats: Pourtalès Terrace (200-450 m) and Miami Terrace (270-600 m). Results suggest that bottom waters along the northern/western slope of the Straits are comprised primarily of the North Atlantic Central Water (NWCW) and Antarctic Intermediate Water (AAIW), driven by upwelling associated with the bottom Ekman transport of the Florida Current. Over the Pourtalès Terrace, both the meandering of the Florida Current and mesoscale eddies modulate the upwelling (downwelling) of cold (warm) waters. In contrast, Florida Current makes a sharp turn at the southern end of the Miami Terrace leading to persistent island wakes, frequent occurrences of a transient eddy, and strong upwelling of deep waters toward the platform of the terrace. Passage of the transient eddy often accompanies strong downwelling of warm waters and a return (southward) flow on top of the platform. Overall, bottom water properties including temperature (T), dissolved inorganic carbon (DIC) and total alkalinity (TA) show strong variability on weekly to monthly time-scales over entire Pourtalès Terrace and on the platform of Miami Terrace mostly driven by physics. In deeper areas (>400 m), bottom water properties are fairly stable with both DIC and TA showing narrow ranges. Interestingly, waters over the southeastern portion of the Pourtalès Terrace show consistently warmer temperature, lower DIC, and higher TA than those on top of this terrace. The aragonite saturation state (Ω) ranges from 1.2-2 on top of the Pourtalès Terrace and 1.2-1.7 both on top of Miami Terrace and on the upper slope of Pourtalès Terrace. In the deeper slope areas (>400 m), it is nearly constant at 1.2-1.3. This modeling effort suggests that remote forcing and biogeochemical processes along the transport paths, from the Gulf of Mexico to the Straits, are significant but second-order contributors to the variability of bottom carbonate chemistry. The impacts of benthic biogeochemical processes along the transit paths are not resolved.

Abstract:

The ability to routinely quantify global carbon dioxide (CO₂) absorption by the oceans has become crucial: it provides a powerful constraint for establishing global and regional carbon (C) budgets, and enables identification of the ecological impacts and risks of this uptake on the marine environment. Advances in understanding, technology, and international coordination have made it possible to measure CO₂ absorption by the oceans to a greater degree of accuracy than is possible in terrestrial landscapes. These advances, combined with new satellite‐based Earth observation capabilities, increasing public availability of data, and cloud computing, provide important opportunities for addressing critical knowledge gaps. Furthermore, Earth observation in synergy with in‐situ monitoring can provide the large‐scale ocean monitoring that is necessary to support policies to protect ocean ecosystems at risk, and motivate societal shifts toward meeting C emissions targets; however, sustained effort will be needed.

Abstract:

A high-quality dataset of surface water fugacity of CO₂ (fCO_2w), consisting of over a million observations, and derived products are presented for the northern Caribbean Sea, covering the time span from 2002 through 2018. Prior to installation of automated pCO₂ systems on cruise ships of Royal Caribbean International and subsidiaries, very limited surface water carbon data were available in this region. With this observational program, the northern Caribbean Sea has now become one of the best-sampled regions for pCO₂ of the world ocean. The dataset and derived quantities are binned and averaged on a 1° monthly grid and are available at http://accession.nodc.noaa.gov/0207749 (last access: 30 June 2020) (https://doi.org/10.25921/2swk-9w56; Wanninkhof et al., 2019a). The derived quantities include total alkalinity (TA), acidity (pH), aragonite saturation state (Ω_Ar), and air-sea CO₂ flux and cover the region from 15–28°N and 88–62°W. The gridded data and products are used for determination of status and trends of ocean acidification, for quantifying air-sea CO₂ fluxes, and for ground-truthing models. Methodologies to derive the TA, pH, and Ω_Ar and to calculate the fluxes from fCO_2w temperature and salinity are described.

Abstract:

Decadal variability of carbonate chemistry variables has been studied for the open ocean using observations and models, but less is known about the variations in the coastal ocean due to observational gaps and the more complex environments. In this work, we use a Bayesian‐neural‐network approach to reconstruct surface carbonate chemistry variables for the Mid‐Atlantic Bight (MAB) and the South Atlantic Bight (SAB) along the North American East Coast from 1982 to 2015. The reconstructed monthly time series data suggest that the rate of f CO₂ increase in the MAB (18 ± 1 μatm per decade) is faster than those in the SAB (14 ± 1 μatm per decade) and the open ocean (14 ± 1 μatm per decade). Correspondingly, pH decreases faster in the MAB. The observed stagnation in the aragonite saturation state, Ω_arag decrease during 2005–2015 in the MAB, is attributed to the intrusion of water from southern and offshore regions with high Ω_arag, which offsets the decrease expected from anthropogenic CO₂ uptake. Furthermore, seasonal asymmetry in the evolution of long‐term change leads to the faster change in the amplitudes of the seasonal cycle in carbonate chemistry variables in coastal waters than those in the open ocean. In particular, the increase in the seasonal‐cycle amplitude of dissolved inorganic carbon in the MAB is 2.9 times larger than that of the open ocean. This leads to the faster increase in the season‐cycle amplitude of Ω_arag and earlier occurrence of undersaturation in coastal waters as acidification continues.

Abstract:

We estimate anthropogenic carbon (C_anth) accumulation rates in the Pacific Ocean between 1991 and 2017 from 14 hydrographic sections that have been occupied two to four times over the past few decades, with most sections having been recently measured as part of the Global Ocean Ship‐based Hydrographic Investigations Program. The rate of change of C_anth is estimated using a new method that combines the extended multiple linear regression method with improvements to address the challenges of analyzing multiple occupations of sections spaced irregularly in time. The C_anth accumulation rate over the top 1,500 m of the Pacific increased from 8.8 (±1.1, 1σ) Pg of carbon per decade between 1995 and 2005 to 11.7 (±1.1) PgC per decade between 2005 and 2015. For the entire Pacific, about half of this decadal increase in the accumulation rate is attributable to the increase in atmospheric CO₂, while in the South Pacific subtropical gyre this fraction is closer to one fifth. This suggests a substantial enhancement of the accumulation of C_anth in the South Pacific by circulation variability and implies that a meaningful portion of the reinvigoration of the global CO₂ sink that occurred between ~2000 and ~2010 could be driven by enhanced ocean C_anth uptake and advection into this gyre. Our assessment suggests that the accuracy of C_anth accumulation rate reconstructions along survey lines is limited by the accuracy of the full suite of hydrographic data and that a continuation of repeated surveys is a critical component of future carbon cycle monitoring.

Abstract:

Surface seawater partial pressure of CO₂ (pCO₂) is a critical parameter in the quantification of air-sea CO₂ flux, which further plays an important role in quantifying the global carbon budget and understanding ocean acidification. Yet, the remote estimation of pCO₂ in coastal waters (under influences of multiple processes) has been difficult due to complex relationships between environmental variables and surface pCO₂. To date there is no unified model to remotely estimate surface pCO₂ in oceanic regions that are dominated by different oceanic processes. In our study area, the Gulf of Mexico (GOM), this challenge is addressed through the evaluation of different approaches, including multi-linear regression (MLR), multi-nonlinear regression (MNR), principle component regression (PCR), decision tree, supporting vector machines (SVMs), multilayer perceptron neural network (MPNN), and random forest based regression ensemble (RFRE). After modeling, validation, and extensive tests using independent cruise datasets, the RFRE model proved to be the best approach. The RFRE model was trained using data comprised of extensive pCO₂ datasets (collected over 16 years by many groups) and MODIS (Moderate Resolution Imaging Spectroradiometer) estimated sea surface temperature (SST), sea surface salinity (SSS), surface chlorophyll concentration (Chl), and diffuse attenuation of downwelling irradiance (Kd). This RFRE-based pCO₂ model allows for the estimation of surface pCO₂ from satellites with a spatial resolution of ~1 km. It showed an overall performance of a root mean square difference (RMSD) of 9.1 μatm, with a coefficient of determination (R²) of 0.95, a mean bias (MB) of −0.03 μatm, a mean ratio (MR) of 1.00, an unbiased percentage difference (UPD) of 0.07%, and a mean ratio difference (MRD) of 0.12% for pCO₂ ranging between 145 and 550 μatm. The model, with its original parameterization, has been tested with independent datasets collected over the entire GOM, with satisfactory performance in each case (RMSD of ≤~10 μatm for open GOM waters and RMSD of ≤~25 μatm for coastal and river-dominated waters). The sensitivity of the RFRE-based pCO₂ model to uncertainties of each input environmental variable was also thoroughly examined. The results showed that all induced uncertainties were close to, or within, the uncertainty of the model itself with higher sensitivity to uncertainties in SST and SSS than to uncertainties in Chl and Kd. The extensive validation, evaluation, and sensitivity analysis indicate the robustness of the RFRE model in estimating surface pCO₂ for the range of 145–550 μatm in most GOM waters. The RFRE model approach was applied to the Gulf of Maine (a contrasting oceanic region to GOM), with local model training. The results showed significant improvement over other models suggesting that the RFRE may serve as a robust approach for other regions once sufficient field-measured pCO₂ data are available for model training.

Abstract:

No abstract.

Abstract:

The tropical Atlantic is home to multiple coupled climate variations covering a wide range of timescales and impacting societally relevant phenomena such as continental rainfall, Atlantic hurricane activity, oceanic biological productivity, and atmospheric circulation in the equatorial Pacific. The tropical Atlantic also connects the southern and northern branches of the Atlantic meridional overturning circulation and receives freshwater input from some of the world’s largest rivers. To address these diverse, unique, and interconnected research challenges, a rich network of ocean observations has developed, building on the backbone of the Prediction and Research Moored Array in the Tropical Atlantic (PIRATA). This network has evolved naturally over time and out of necessity in order to address the most important outstanding scientific questions and to improve predictions of tropical Atlantic severe weather and global climate variability and change. The tropical Atlantic observing system is motivated by goals to understand and better predict phenomena such as tropical Atlantic interannual to decadal variability and climate change; multidecadal variability and its links to the meridional overturning circulation; air-sea fluxes of CO₂ and their implications for the fate of anthropogenic CO₂; the Amazon River plume and its interactions with biogeochemistry, vertical mixing, and hurricanes; the highly productive eastern boundary and equatorial upwelling systems; and oceanic oxygen minimum zones, their impacts on biogeochemical cycles and marine ecosystems, and their feedbacks to climate. Past success of the tropical Atlantic observing system is the result of an international commitment to sustained observations and scientific cooperation, a willingness to evolve with changing research and monitoring needs, and a desire to share data openly with the scientific community and operational centers. The observing system must continue to evolve in order to meet an expanding set of research priorities and operational challenges. This paper discusses the tropical Atlantic observing system, including emerging scientific questions that demand sustained ocean observations, the potential for further integration of the observing system, and the requirements for sustaining and enhancing the tropical Atlantic observing system.

Abstract:

We quantify the oceanic sink for anthropogenic carbon dioxide (CO₂) over the period 1994 to 2007 by using observations from the global repeat hydrography program and contrasting them to observations from the 1990s. Using a linear regression–based method, we find a global increase in the anthropogenic CO₂ inventory of 34 ± 4 petagrams of carbon (Pg C) between 1994 and 2007. This is equivalent to an average uptake rate of 2.6 ± 0.3 Pg C year⁻¹ and represents 31 ± 4% of the global anthropogenic CO₂ emissions over this period. Although this global ocean sink estimate is consistent with the expectation of the ocean uptake having increased in proportion to the rise in atmospheric CO₂, substantial regional differences in storage rate are found, likely owing to climate variability–driven changes in ocean circulation.

Abstract:

The Global Ocean Data Analysis Project (GLODAP) is a synthesis effort providing regular compilations of surface to bottom ocean biogeochemical data, with an emphasis on seawater inorganic carbon chemistry and related variables determined through chemical analysis of water samples. This update of GLODAPv2, v2.2019, adds data from 116 cruises to the previous version, extending its coverage in time from 2013 to 2017, while also adding some data from prior years. GLODAPv2.2019 includes measurements from more than 1.1 million water samples from the global oceans collected on 840 cruises. The data for the 12 GLODAP core variables (salinity, oxygen, nitrate, silicate, phosphate, dissolved inorganic carbon, total alkalinity, pH, CFC-11, CFC-12, CFC-113, and CCl₄) have undergone extensive quality control, especially systematic evaluation of bias. The data are available in two formats: (i) as submitted by the data originator but updated to WOCE exchange format and (ii) as a merged data product with adjustments applied to minimize bias. These adjustments were derived by comparing the data from the 116 new cruises with the data from the 724 quality-controlled cruises of the GLODAPv2 data product. They correct for errors related to measurement, calibration, and data handling practices, taking into account any known or likely time trends or variations. The compiled and adjusted data product is believed to be consistent to better than 0.005 in salinity, 1 % in oxygen, 2 % in nitrate, 2 % in silicate, 2 % in phosphate, 4 µmol kg⁻¹ in dissolved inorganic carbon, 4 µmol kg⁻¹ in total alkalinity, 0.01–0.02 in pH, and 5 % in the halogenated transient tracers. The compilation also includes data for several other variables, such as isotopic tracers. These were not subjected to bias comparison or adjustments. The original data, their documentation and DOI codes are available in the Ocean Carbon Data System of NOAA NCEI (https://www.nodc.noaa.gov/ocads/oceans/GLODAPv2_2019/, last access: 17 September 2019). This site also provides access to the merged data product, which is provided as a single global file and as four regional ones – the Arctic, Atlantic, Indian, and Pacific oceans – under https://doi.org/10.25921/xnme-wr20 (Olsen et al., 2019). The product files also include significant ancillary and approximated data. These were obtained by interpolation of, or calculation from, measured data. This paper documents the GLODAPv2.2019 methods and provides a broad overview of the secondary quality control procedures and results.

Abstract:

The Argo Program has been implemented and sustained for almost two decades, as a global array of about 4000 profiling floats. Argo provides continuous observations of ocean temperature and salinity versus pressure, from the sea surface to 2000 dbar. The successful installation of the Argo array and its innovative data management system arose opportunistically from the combination of great scientific need and technological innovation. Through the data system, Argo provides fundamental physical observations with broad societally-valuable applications, built on the cost-efficient and robust technologies of autonomous profiling floats. Following recent advances in platform and sensor technologies, even greater opportunity exists now than 20 years ago to (i) improve Argo’s global coverage and value beyond the original design, (ii) extend Argo to span the full ocean depth, (iii) add biogeochemical sensors for improved understanding of oceanic cycles of carbon, nutrients, and ecosystems, and (iv) consider experimental sensors that might be included in the future, for example to document the spatial and temporal patterns of ocean mixing. For Core Argo and each of these enhancements, the past, present, and future progression along a path from experimental deployments to regional pilot arrays to global implementation is described. The objective is to create a fully global, top-to-bottom, dynamically complete, and multidisciplinary Argo Program that will integrate seamlessly with satellite and with other in situ elements of the Global Ocean Observing System (Legler et al., 2015). The integrated system will deliver operational reanalysis and forecasting capability, and assessment of the state and variability of the climate system with respect to physical, biogeochemical, and ecosystems parameters. It will enable basic research of unprecedented breadth and magnitude, and a wealth of ocean-education and outreach opportunities.

Abstract:

No abstract.

Abstract:

The Global Ocean Ship-Based Hydrographic Investigations Program (GO-SHIP) provides a globally coordinated network and oversight of 55 sustained decadal repeat hydrographic reference lines. GO-SHIP is part of the global ocean/climate observing systems (GOOS/GCOS) for study of physical oceanography, the ocean carbon, oxygen and nutrient cycles, and marine biogeochemistry. GO-SHIP enables assessment of the ocean sequestration of heat and carbon, changing ocean circulation and ventilation patterns, and their effects on ocean health and Earth’s climate. Rapid quality control and open data release along with incorporation of the GO-SHIP effort in the Joint Technical Commission for Oceanography and Marine Meteorology (JCOMM) in situ Observing Programs Support Center (JCOMMOPS) have increased the profile of, and participation in, the program and led to increased data use for a range of efforts. In addition to scientific discovery, GO-SHIP provides climate quality observations for ongoing calibration of measurements from existing and new autonomous platforms. This includes biogeochemical observations for the nascent array of biogeochemical (BGC)-Argo floats; temperature and salinity for Deep Argo; and salinity for the core Argo array. GO-SHIP provides the relevant suite of global, full depth, high quality observations and co-located deployment opportunities that, for the foreseeable future, remain crucial to maintenance and evolution of Argo’s unique contribution to climate science. The evolution of GO-SHIP from a program primarily focused on physical climate to increased emphasis on ocean health and sustainability has put an emphasis on the addition of essential ocean variables for biology and ecosystems in the program measurement suite. In conjunction with novel automated measurement systems, ocean color, particulate matter, and phytoplankton enumeration are being explored as GO-SHIP variables. The addition of biological and ecosystem measurements will enable GO-SHIP to determine trends and variability in these key indicators of ocean health. The active and adaptive community has sustained the network, quality and relevance of the global repeat hydrography effort through societally important scientific results, increased exposure, and interoperability with new efforts and opportunities within the community. Here we provide key recommendations for the continuation and growth of GO‑SHIP in the next decade.

Abstract:

Sixteen years of surface water CO₂ data from autonomous systems on cruise ships sailing in the Caribbean Sea and Western North Atlantic show marked changes on interannual timescales. The measured changes in fugacity (≈partial pressure) of CO₂ in surface water, fCO_2w, are based on over a million observations. Seasonally the patterns are similar to other oligotrophic subtropical regions with an amplitude of fCO_2w of ≈40 μatm with low wintertime values, causing the area to be a sink, and high summertime values making it a source of CO₂ to the atmosphere. On annual scales there was negligible increase of fCO_2w from 2002 to 2010 and a rapid increase from 2010 to 2018. Correspondingly, the trend of air‐sea CO₂ flux from 2002 to 2010 was strongly negative (increasing uptake or sink) at −0.05 ± 0.01 (mol m⁻² year⁻¹) year⁻¹ and positive (decreasing uptake) at 0.02 ± 0.02 (mol m⁻² year⁻¹) year⁻¹ from 2010‐2018. For the whole period from 2002 to 2018, the fCO_2w lagged the atmospheric CO₂ increase by 24 %, causing an increase in CO₂ uptake. The average flux into the ocean for the 16 years is −0.20 ± 0.16 mol m⁻² year⁻¹ with the uncertainty reflecting the standard deviation in annual means. The change in multiannual trend in fCO_2w is modulated by several factors, notably changes in sea surface temperature and ocean mixed layer depth that, in turn, affected the physical and biological processes controlling fCO_2w.

Abstract:

The Surface Ocean CO₂ NETwork (SOCONET) and atmospheric Marine Boundary Layer (MBL) CO₂ measurements from ships and buoys focus on the operational aspects of measurements of CO₂ in both the ocean surface and atmospheric MBLs. The goal is to provide accurate pCO₂ data to within 2 micro atmosphere (μatm) for surface ocean and 0.2 parts per million (ppm) for MBL measurements following rigorous best practices, calibration and intercomparison procedures. Platforms and data will be tracked in near real-time and final quality-controlled data will be provided to the community within a year. The network, involving partners worldwide, will aid in production of important products such as maps of monthly resolved surface ocean CO₂ and air-sea CO₂ flux measurements. These products and other derivatives using surface ocean and MBL CO₂ data, such as surface ocean pH maps and MBL CO₂ maps, will be of high value for policy assessments and socio-economic decisions regarding the role of the ocean in sequestering anthropogenic CO₂ and how this uptake is impacting ocean health by ocean acidification. SOCONET has an open ocean emphasis but will work with regional (coastal) networks. It will liaise with intergovernmental science organizations such as Global Atmosphere Watch (GAW), and the joint committee for and ocean and marine meteorology (JCOMM). Here we describe the details of this emerging network and its proposed operations and practices.

Abstract:

No abstract.

Abstract:

No abstract.

Abstract:

Although the Southern Ocean is thought to account for a significant portion of the contemporary oceanic uptake of carbon dioxide (CO₂), flux estimates in this region are based on sparse observations that are strongly biased toward summer. Here we present new estimates of Southern Ocean air‐sea CO₂ fluxes calculated with measurements from biogeochemical profiling floats deployed by the Southern Ocean Carbon and Climate Observations and Modeling project during 2014–2017. Compared to ship‐based CO₂ flux estimates, the float‐based fluxes find significantly stronger outgassing in the zone around Antarctica where carbon‐rich deep waters upwell to the surface ocean. Although interannual variability contributes, this difference principally stems from the lack of autumn and winter ship‐based observations in this high‐latitude region. These results suggest that our current understanding of the distribution of oceanic CO₂ sources and sinks may need revision and underscore the need for sustained year‐round biogeochemical observations in the Southern Ocean.

Abstract:

The West Florida Shelf (WFS) is a source of uncertainty for the Gulf of Mexico carbon budget. Data from the synthesis of approximately 135,000 pCO₂ values from 97 cruises from the WFS show that the shelf waters fluctuate between being a weak source to a weak sink of carbon. Overall, the shelf acts as a weak source of CO₂ at 0.32 ± 1.5 mol m⁻² yr⁻¹. Subregions, however, reveal slightly different trends, where surface waters associated with 40–200‐m isobath in the northern and southern WFS are generally weak sinks all year, except for summer when they act as sources of CO₂. Conversely, nearshore waters (2, particularly the southern shallow waters, which are a source all year round. The pCO₂ of seawater has been increasing at a rate of approximately 4.37 μatm/year as compared to atmospheric pCO₂ which has increased at a rate of about 1.7 μatm per year from 1996 to 2016. The annual CO₂ flux has increased from −0.78 to 0.92 mol m⁻² yr⁻¹ on the shelf from 1996–2016. The WFS is emitting 9.23 Tg C/year, with the southern nearshore region emitting the most at 9.01 Tg C/year and the northern region acting as a sink of −1.96 Tg C/year. Aragonite saturation state on the WFS shows seasonal and geographic trends with values ranging from 2 to 5. Lowest values are found in winter associated with subregion <40‐m isobath.

Abstract:

The Southern Ocean is central to the global climate and the global carbon cycle, and to the climate's response to increasing levels of atmospheric greenhouse gases, as it ventilates a large fraction of the global ocean volume. Global coupled climate models and earth system models, however, vary widely in their simulations of the Southern Ocean and its role in, and response to, the ongoing anthropogenic trend. Due to the region's complex water‐mass structure and dynamics, Southern Ocean carbon and heat uptake depend on a combination of winds, eddies, mixing, buoyancy fluxes, and topography. Observationally-based metrics are critical for discerning processes and mechanisms and for validating and comparing climate and earth system models. New observations and understanding have allowed for progress in the creation of observationally-based data/model metrics for the Southern Ocean. Metrics presented here provide a means to assess multiple simulations relative to the best available observations and observational products. Climate models that perform better according to these metrics also better simulate the uptake of heat and carbon by the Southern Ocean. This report is not strictly an intercomparison, but rather a distillation of key metrics that can reliably quantify the “accuracy” of a simulation against observed, or at least observable, quantities. One overall goal is to recommend standardization of observationally-based benchmarks that the modeling community should aspire to meet to reduce uncertainties in climate projections, especially uncertainties related to oceanic heat and carbon uptake.

Abstract:

While the effects of the Southern Annular Mode (SAM), a dominant climate variability mode in the Southern Ocean, on ocean acidification have been examined using models, no consensus has been reached. Using observational data from south of Tasmania, we show that during a period with positive SAM trends, surface water pH and aragonite saturation state at 60°–55°S (Antarctic Zone) decrease in austral summer at rates faster than those predicted from atmospheric CO₂ increase alone, whereas an opposite pattern is observed at 50°–45°S (Subantarctic Zone). Together with other processes, the enhanced acidification at 60°–55°S may be attributed to increased westerly winds that bring in more “acidified” waters from the higher latitudes via enhanced meridional Ekman transport and from the subsurface via increased vertical mixing. Our observations support climatic modulation of ocean acidification superimposed on the effect of increasing atmospheric CO₂.

Abstract:

We estimated monthly air–sea CO₂ fluxes in the Arctic Ocean and its adjacent seas north of 60° N from 1997 to 2014. This was done by mapping partial pressure of CO₂ in the surface water (pCO_2w) using a self-organizing map (SOM) technique incorporating chlorophyll a concentration (Chl a), sea surface temperature, sea surface salinity, sea ice concentration, atmospheric CO₂ mixing ratio, and geographical position. We applied new algorithms for extracting Chl a from satellite remote sensing reflectance with close examination of uncertainty of the obtained Chl a values. The overall relationship between pCO_2w and Chl a was negative, whereas the relationship varied among seasons and regions. The addition of Chl a as a parameter in the SOM process enabled us to improve the estimate of pCO_2w, particularly via better representation of its decline in spring, which resulted from biologically mediated pCO_2w reduction. As a result of the inclusion of Chl a, the uncertainty in the CO₂ flux estimate was reduced, with a net annual Arctic Ocean CO₂ uptake of 180 ± 130 Tg C yr⁻¹. Seasonal to interannual variation in the CO₂ influx was also calculated.

Abstract:

No abstract.

Abstract:

Nutrient inputs from the Mississippi/Atchafalaya River system into the northern Gulf of Mexico promote high phytoplankton production and lead to high respiration rates. Respiration coupled with water column stratification results in seasonal summer hypoxia in bottom waters on the shelf. In addition to consuming oxygen, respiration produces carbon dioxide (CO₂), thus lowering the pH and acidifying bottom waters. Here we present a high-resolution biogeochemical model simulating this eutrophication-driven acidification and investigate the dominant underlying processes. The model shows the recurring development of an extended area of acidified bottom waters in summer on the northern Gulf of Mexico shelf that coincides with hypoxic waters. Not reported before, acidified waters are confined to a thin bottom boundary layer where the production of CO₂ by benthic metabolic processes is dominant. Despite a reduced saturation state, acidified waters remain supersaturated with respect to aragonite.

Abstract:

Since late 1978, Antarctic sea-ice extent in the East Pacific has retreated persistently over the Amundsen and Bellingshausen Seas in warm seasons, but expanded over the Ross and Amundsen Seas in cold seasons, while almost opposite seasonal trends have occurred in the Atlantic over the Weddell Sea. By using a surface-forced ocean and sea-ice coupled model, we show that regional wind-driven ocean dynamics played a key role in driving these trends. In the East Pacific, the strengthening Southern Hemisphere (SH) westerlies in the region enhanced the Ekman upwelling of warm upper Circumpolar Deep Water and increased the northward Ekman transport of cold Antarctic surface water. The associated surface ocean warming south of 68°S and the cooling north of 68°S directly contributed to the retreat of sea-ice in warm seasons and the expansion in cold seasons, respectively. In the Atlantic, the poleward shifting SH westerlies in the region strengthened the northern branch of the Weddell Gyre which, in turn, increased the meridional thermal gradient across it as constrained by the thermal wind balance. Ocean heat budget analysis further suggests that the strengthened northern branch of the Weddell Gyre acted as a barrier against the poleward ocean heat transport, and thus produced anomalous heat divergence within the Weddell Gyre and anomalous heat convergence north of the gyre. The associated cooling within the Weddell Gyre and the warming north of the gyre contributed to the expansion of sea-ice in warm seasons and the retreat in cold seasons, respectively.

Abstract:

Marine carbonate system monitoring programs often consist of multiple observational methods that include underway cruise data, moored autonomous time series, and discrete water bottle samples. Monitored parameters include all, or some, of the following: partial pressure of CO₂ of the water (pCO_2w) and air, dissolved inorganic carbon (DIC), total alkalinity (TA), and pH. Any combination of at least two of the aforementioned parameters can be used to calculate the others. In this study at the Gray's Reef (GR) mooring in the South Atlantic Bight (SAB) we: examine the internal consistency of pCO_2w from an underway cruise, moored autonomous time series, and calculated from bottle samples (DIC-TA pairing); describe the seasonal to interannual pCO_2w time series variability and air-sea flux (FCO₂), as well as describe the potential sources of pCO_2w variability; and determine the source/sink for atmospheric pCO₂. Over the ~8.5 years of GR mooring time series, mooring-underway and mooring-bottle calculated-pCO_2w strongly correlate with r-values >0.90. pCO_2w and FCO₂ time series follow seasonal thermal patterns; however, seasonal non-thermal processes, such as terrestrial export, net biological production, and air-sea exchange also influence variability. The linear slope of time series pCO_2w increases by 5.2±1.4 µatm y⁻¹ with FCO₂ increasing 51 to 70 mmol m⁻² y⁻¹. The net FCO₂ sign can switch interannually with the magnitude varying greatly. Non-thermal pCO_2w is also increasing over the time series, likely indicating that terrestrial export and net biological processes drive the long term pCO_2w increase.

Abstract:

This work describes an improved algorithm for spectrophotometric determinations of seawater carbonate ion concentrations ([CO₃^2–]_spec) derived from observations of ultraviolet absorbance spectra in lead-enriched seawater. Quality-control assessments of [CO₃^2–]_spec data obtained on two NOAA research cruises (2012 and 2016) revealed a substantial intercruise difference in average Δ[CO₃^2–] (the difference between a sample’s [CO₃^2–]_spec value and the corresponding [CO₃^2–] value calculated from paired measurements of pH and dissolved inorganic carbon). Follow-up investigation determined that this discordance was due to the use of two different spectrophotometers, even though both had been properly calibrated. Here we present an essential methodological refinement to correct [CO₃^2–]_spec absorbance data for small but significant instrumental differences. After applying the correction (which, notably, is not necessary for pH determinations from sulfonephthalein dye absorbances) to the shipboard absorbance data, we fit the combined-cruise data set to produce empirically updated parameters for use in processing future (and historical) [CO₃^2–]_spec absorbance measurements. With the new procedure, the average Δ[CO₃^2–] offset between the two aforementioned cruises was reduced from 3.7 μmol kg^–1 to 0.7 μmol kg^–1, which is well within the standard deviation of the measurements (1.9 μmol kg^–1). We also introduce an empirical model to calculate in situ carbonate ion concentrations from [CO₃^2–]_spec. We demonstrate that these in situ values can be used to determine calcium carbonate saturation states that are in good agreement with those determined by more laborious and expensive conventional methods.

Abstract:

Variability and change in the ocean sink of anthropogenic carbon dioxide (CO₂) have implications for future climate and ocean acidification. Measurements of surface seawater CO₂ partial pressure (pCO₂) and wind speed from moored platforms are used to calculate high-resolution CO₂ flux time series. Here we use the moored CO₂ fluxes to examine variability and its drivers over a range of time scales at four locations in the Pacific Ocean. There are significant surface seawater pCO₂, salinity, and wind speed trends in the North Pacific subtropical gyre, especially during winter and spring, which reduce CO₂ uptake over the 10 year record of this study. Starting in late 2013, elevated seawater pCO₂ values driven by warm anomalies cause this region to be a net annual CO₂ source for the first time in the observational record, demonstrating how climate forcing can influence the timing of an ocean region shift from CO₂ sink to source.

Abstract:

No abstract.

Abstract:

An increase in global wind speeds over time is affecting the global uptake of CO₂ by the ocean. We determine the impact of changing winds on gas transfer and CO₂ uptake by using the recently updated, global high-resolution, cross-calibrated multiplatform wind product (CCMP-V2) and a fixed monthly pCO₂ climatology. In particular, we assess global changes in the context of regional wind speed changes that are attributed to large-scale climate reorganizations. The impact of wind on global CO₂ gas fluxes as determined by the bulk formula is dependent on several factors, including the functionality of the gas exchange-wind speed relationship and the regional and seasonal differences in the air-water partial pressure of CO₂ gradient (ΔpCO₂). The latter also controls the direction of the flux. Fluxes out of the ocean are influenced more by changes in the low-to-intermediate wind speed range, while ingassing is impacted more by changes in higher winds because of the regional correlations between wind and ΔpCO₂. Gas exchange-wind speed parameterizations with a quadratic and third-order polynomial dependency on wind, each of which meets global constraints, are compared. The changes in air-sea CO₂ fluxes resulting from wind speed trends are greatest in the equatorial Pacific and cause a 0.03–0.04 Pg C decade⁻¹ increase in outgassing over the 27 year time span. This leads to a small overall decrease of 0.00 to 0.02 Pg C decade⁻¹ in global net CO₂ uptake, contrary to expectations that increasing winds increase net CO₂ uptake.

Abstract:

More than 74 biogeochemical profiling floats that measure water column pH, oxygen, nitrate, fluorescence, and backscattering at 10-day intervals have been deployed throughout the Southern Ocean. Calculating the surface ocean partial pressure of carbon dioxide (pCO_2sw) from float pH has uncertainty contributions from the pH sensor, the alkalinity estimate, and carbonate system equilibrium constants, resulting in a relative standard uncertainty in pCO_2sw of 2.4% (or 10 µatm at pCO_2sw of 400 µatm). The calculated pCO_2sw from several floats spanning a range of oceanographic regimes are compared to existing climatologies. In some locations, such as the Subantarctic zone, the float data closely match the climatologies, but in the Polar Antarctic Zone significantly higher pCO_2sw are calculated in the wintertime, implying a greater air-sea CO₂ efflux estimate. Our results, based on four representative floats, suggest that despite their uncertainty relative to direct measurements the float data can be used to improve estimates for air-sea carbon flux, as well as to increase knowledge of spatial, seasonal, and interannual variability in this flux.

Abstract:

The uptake of anthropogenic carbon dioxide (CO₂) from the atmosphere has resulted in a decrease in seawater aragonite saturation state (Ω_arag), which affects the health of carbonate-bearing organisms and the marine ecosystem. A substantial short-term variability of surface water Ω_arag, with an increase of up to 0.32, was observed in the central Mid-Atlantic Bight off the Delaware and the Chesapeake Bays over a short period of 10 days in summer 2015. High-frequency underway measurements for temperature, salinity, percentage saturation of dissolved oxygen, oxygen to argon ratio, pH, fCO₂, and measurements based on discrete samples for pH, dissolved inorganic carbon, and total alkalinity are used to investigate how physical and biogeochemical processes contribute to the changes of Ω_arag. Quantitative analyses show that physical advection and mixing processes are the dominant forces for higher Ω_arag in slope waters while biological carbon removal and CO₂ degassing contribute to increased Ω_arag in shelf waters.

Abstract:

The fugacity of CO₂ (fCO₂ (water)) and air-water CO₂ flux were compared between a river-dominated anthropogenically disturbed open estuary, the Hugli, and a comparatively pristine mangrove-dominated semiclosed marine estuary, the Matla, on the east coast of India. Annual mean salinity of the Hugli Estuary (≈7.1) was much less compared to the Matla Estuary (≈20.0). All the stations of the Hugli Estuary were highly supersaturated with CO₂ (annual mean ~ 2200 µatm), whereas the Matla was marginally oversaturated (annual mean ~ 530 µatm). During the postmonsoon season, the outer station of the Matla Estuary was under saturated with respect to CO₂ and acted as a sink. The annual mean CO₂ emission from the Hugli Estuary (32.4 mol C m⁻² yr⁻¹) was 14 times higher than the Matla Estuary (2.3 mol C m⁻² yr⁻¹). CO₂ efflux rate from the Hugli Estuary has increased drastically in the last decade, which is attributed to increased runoff from the river-dominated estuary.

Abstract:

The Surface Ocean CO₂ Atlas (SOCAT) is a synthesis of quality-controlled fCO₂ (fugacity of carbon dioxide) values for the global surface oceans and coastal seas with regular updates. Version 3 of SOCAT has 14.7 million fCO₂ values from 3646 data sets covering the years 1957 to 2014. This latest version has an additional 4.6 million fCO₂ values relative to version 2 and extends the record from 2011 to 2014. Version 3 also significantly increases the data availability for 2005 to 2013. SOCAT has an average of approximately 1.2 million surface water fCO₂ values per year for the years 2006 to 2012. Quality and documentation of the data has improved. A new feature is the data set quality control (QC) flag of E for data from alternative sensors and platforms. The accuracy of surface water fCO₂ has been defined for all data set QC flags. Automated range checking has been carried out for all data sets during their upload into SOCAT. The upgrade of the interactive Data Set Viewer (previously known as the Cruise Data Viewer) allows better interrogation of the SOCAT data collection and rapid creation of high-quality figures for scientific presentations. Automated data upload has been launched for version 4 and will enable more frequent SOCAT releases in the future. High-profile scientific applications of SOCAT include quantification of the ocean sink for atmospheric carbon dioxide and its long-term variation, detection of ocean acidification, as well as evaluation of coupled-climate and ocean-only biogeochemical models. Users of SOCAT data products are urged to acknowledge the contribution of data providers, as stated in the SOCAT Fair Data Use Statement. This ESSD (Earth System Science Data) “living data” publication documents the methods and data sets used for the assembly of this new version of the SOCAT data collection and compares these with those used for earlier versions of the data collection (Pfeil et al., 2013; Sabine et al., 2013; Bakker et al., 2014). Individual data set files, included in the synthesis product, can be downloaded here: doi:10.1594/PANGAEA.849770. The gridded products are available here: doi:10.3334/CDIAC/OTG.SOCAT_V3_GRID.

Abstract:

No abstract.

Abstract:

GasEx-98 was the first open-ocean process study where gas transfer velocity measurements were made with several robust techniques, including airside eddy covariance of CO₂ and deliberate injection of ³He and SF₆. While the CO₂ eddy covariance results have been fully analyzed and publicized, leading to a boom in the use of this technique in the marine environment, the ³He/SF₆ results have not received the same level of analysis. Here, based on new approaches that we have developed to analyse ³He/SF₆ data in the subsequent years, we revisit the ³He/SF₆ dual tracer results from GasEx-98 and show that they are consistent with the results from other parts of the coastal and open ocean, and that they are in agreement with current parameterizations between wind speed and gas exchange for slightly soluble gases over the ocean at intermediate wind speeds.

Abstract:

Global ship-based programs, with highly accurate, full water column physical and biogeochemical observations repeated decadally since the 1970s, provide a crucial resource for documenting ocean change. The ocean, a central component of Earth’s climate system, is taking up most of Earth's excess anthropogenic heat, with about 19% of this excess in the abyssal ocean beneath 2,000 m, dominated by Southern Ocean warming. The ocean also has taken up about 27% of anthropogenic carbon, resulting in acidification of the upper ocean. Increased stratification has resulted in a decline in oxygen and increase in nutrients in the Northern Hemisphere thermocline and an expansion of tropical oxygen minimum zones. Southern Hemisphere thermocline oxygen increased in the 2000s owing to stronger wind forcing and ventilation. The most recent decade of global hydrography has mapped dissolved organic carbon, a large, bioactive reservoir, for the first time and quantified its contribution to export production (∼20%) and deep-ocean oxygen utilization. Ship-based measurements also show that vertical diffusivity increases from a minimum in the thermocline to a maximum within the bottom 1,500 m, shifting our physical paradigm of the ocean’s overturning circulation.

Abstract:

No abstract.

Abstract:

Empirical algorithms are developed using high-quality GO-SHIP hydrographic measurements of commonly measured parameters (temperature, salinity, pressure, nitrate, and oxygen) that estimate pH in the Pacific sector of the Southern Ocean. The coefficients of determination, R², are 0.98 for pH from nitrate (pH^N) and 0.97 for pH from oxygen (pH^Ox) with RMS errors of 0.010 and 0.008, respectively. These algorithms are applied to Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) biogeochemical profiling floats, which include novel sensors (pH, nitrate, oxygen, fluorescence, and backscatter). These algorithms are used to estimate pH on floats with no pH sensors and to validate and adjust pH sensor data from floats with pH sensors. The adjusted float data provide, for the first time, seasonal cycles in surface pH on weekly resolution that range from 0.05 to 0.08 on weekly resolution for the Pacific sector of the Southern Ocean.

Abstract:

The extended multilinear regression method is used to determine the uptake and storage of anthropogenic carbon in the Atlantic Ocean based on repeat occupations of four cruises from 1989 to 2014 (A16, A20, A22, and A10), with an emphasis on the 2003-2014 period. The results show a significant increase in basin-wide anthropogenic carbon storage in the North Atlantic, which absorbed 4.4 ± 0.9 Pg C decade^–1 from 2003 to 2014 compared to 1.9 ± 0.4 Pg C decade^–1 for the 1989-2003 period. This decadal variability is attributed to changing ventilation patterns associated with the North Atlantic Oscillation and increasing release of anthropogenic carbon into the atmosphere. There are small changes in the uptake rate of CO₂ in the South Atlantic for these time periods (3.7 ± 0.8 Pg C decade^–1 versus 3.2 ± 0.7 Pg C decade^–1). Several eddies are identified as containing ~20% more anthropogenic carbon than the surrounding waters in the South Atlantic, demonstrating the importance of eddies in transporting anthropogenic carbon. The uptake of carbon results in a decrease in pH of ~0.0021 ± 0.0007 year^–1 for surface waters during the last 10 years, in line with the atmospheric increase in CO₂.

Abstract:

We produced 204 monthly maps of the air–sea CO₂ flux in the Arctic north of 60°N, including the Arctic Ocean and its adjacent seas, from January 1997 to December 2013 by using a self-organizing map technique. The partial pressure of CO₂ in surface water data were obtained by shipboard underway measurements or calculated from alkalinity and total inorganic carbon of surface water samples. Subsequently, we investigated the basin-wide distribution and seasonal to interannual variability of the CO₂ fluxes. The 17-year annual mean CO₂ flux shows that all areas of the Arctic Ocean and its adjacent seas were net CO₂ sinks. The estimated annual CO₂ uptake by the Arctic Ocean was 180 TgC yr^–1. The CO₂ influx was strongest in winter in the Greenland/Norwegian Seas (>15 mmol m^–2 day^–1) and the Barents Sea (>12 mmol m^–2 day^–1) because of strong winds, and strongest in summer in the Chukchi Sea (∼10 mmol m^–2 day^–1) because of the sea-ice retreat. In recent years, the CO₂ uptake has increased in the Greenland/Norwegian Sea and decreased in the southern Barents Sea, owing to increased and decreased air–sea pCO₂ differences, respectively.

Abstract:

Over the last 5 decades monitoring systems have been developed to detect changes in the accumulation of carbon (C) in the atmosphere and ocean; however, our ability to detect changes in the behavior of the global C cycle is still hindered by measurement and estimate errors. Here we present a rigorous and flexible framework for assessing the temporal and spatial components of estimate errors and their impact on uncertainty in net C uptake by the biosphere. We present a novel approach for incorporating temporally correlated random error into the error structure of emission estimates. Based on this approach, we conclude that the 2σ uncertainties of the atmospheric growth rate have decreased from 1.2 Pg C yr⁻¹ in the 1960s to 0.3 Pg C yr⁻¹ in the 2000s due to an expansion of the atmospheric observation network. The 2σ uncertainties in fossil fuel emissions have increased from 0.3 Pg C yr⁻¹ in the 1960s to almost 1.0 Pg C yr⁻¹ during the 2000s due to differences in national reporting errors and differences in energy inventories. Lastly, while land use emissions have remained fairly constant, their errors still remain high and thus their global C uptake uncertainty is not trivial. Currently, the absolute errors in fossil fuel emissions rival the total emissions from land use, highlighting the extent to which fossil fuels dominate the global C budget. Because errors in the atmospheric growth rate have decreased faster than errors in total emissions have increased, a ~20% reduction in the overall uncertainty of net C global uptake has occurred. Given all the major sources of error in the global C budget that we could identify, we are 93% confident that terrestrial C uptake has increased and 97% confident that ocean C uptake has increased over the last 5 decades. Thus, it is clear that arguably one of the most vital ecosystem services currently provided by the biosphere is the continued removal of approximately half of atmospheric CO₂ emissions from the atmosphere, although there are certain environmental costs associated with this service, such as the acidification of ocean waters.

Abstract:

The accumulation of carbon within the Weddell Gyre and its exchanges across the gyre boundaries are investigated with three recent full-depth oceanographic sections enclosing this climatically-important region. The combination of carbon measurements with ocean circulation transport estimates from a box inverse analysis reveals that deepwater transports associated with Warm Deep Water (WDW) and Weddell Sea Deep Water dominate the gyre's carbon budget, while a dual-cell vertical overturning circulation leads to both upwelling and the delivery of large quantities of carbon to the deep ocean. Historical sea surface pCO₂ observations, interpolated using a neural network technique, confirm the net summertime sink of 0.044-0.058 ± 0.010 Pg C yr^–1 derived from the inversion. However, a wintertime outgassing signal similar in size results in a statistically insignificant annual air-to-sea CO₂ flux of 0.002 ± 0.007 Pg C yr^–1 (mean 1998-2011) to 0.012 ± 0.024 Pg C yr^–1 (mean 2008-2010) to be diagnosed for the Weddell Gyre. A surface layer carbon balance, independently derived from in situ biogeochemical measurements, reveals that freshwater inputs and biological drawdown decrease surface ocean inorganic carbon levels more than they are increased by WDW entrainment, resulting in an estimated annual carbon sink of 0.033 ± 0.021 Pg C yr^–1. Although relatively less efficient for carbon uptake than the global oceans, the summertime Weddell Gyre suppresses the winter outgassing signal, while its biological pump and deepwater formation act as key conduits for transporting natural and anthropogenic carbon to the deep ocean where they can reside for long time scales.

Abstract:

Ammonium is a nutrient frequently preferred by microorganisms that photosynthesizes at the base of the marine food web and removes atmospheric carbon dioxide via carbon fixation. Because their photosynthesis is concentrated in the ocean's thin euphotic zone, its nutrient concentrations are critical to oceanic carbon fixation. Identification of replacement processes for euphotic-zone ammonium thus becomes important. These processes were investigated in a two-experiment, Lagrangian field study that produced results consistent with an apparent inverse effect of wind forcing on upper-ocean ammonium concentrations. At low wind speeds (especially ≤ 4 ms^− 1), continuous seawater sampling, supported by sulfur-hexafluoride (SF6) water-mass tracing and meteorological measurements, detected 1.1–4.4-km-wide boluses of surface seawater exhibiting ammonium enrichments that were 5 - to-10-fold above background. In the first experiment, ammonium maxima comprising the enrichment event disappeared at higher wind speeds. In the second experiment, which had consistently higher wind speeds, an ammonium event composed of such maxima was never found. The apparent correlation between elevated ammonium concentrations and low wind stress could therefore be viewed as potentially important for understanding ammonium cycling and carbon fixation in the ocean.

Abstract:

No abstract.

Abstract: Several studies have suggested that the carbon sink in the Southern Ocean—the ocean’s strongest region for the uptake of anthropogenic CO2—has weakened in recent decades. We demonstrated, on the basis of multidecadal analyses of surface ocean CO2 observations, that this weakening trend stopped around 2002 and, by 2012, the Southern Ocean had regained its expected strength based on the growth of atmospheric CO2. All three Southern Ocean sectors have contributed to this reinvigoration of the carbon sink, yet differences in the processes between sectors exist, related to a tendency toward a zonally more asymmetric atmospheric circulation. The large decadal variations in the Southern Ocean carbon sink suggest a rather dynamic ocean carbon cycle that varies more in time than previously recognized.

Abstract:

Accurate assessment of anthropogenic carbon dioxide (CO₂) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and a methodology to quantify all major components of the global carbon budget, including their uncertainties, based on the combination of a range of data, algorithms, statistics, and model estimates and their interpretation by a broad scientific community. We discuss changes compared to previous estimates, consistency within and among components, alongside methodology and data limitations. CO₂ emissions from fossil fuel combustion and cement production (E_FF) are based on energy statistics and cement production data, respectively, while emissions from land-use change (E_LUC), mainly deforestation, are based on combined evidence from land-cover-change data, fire activity associated with deforestation, and models. The global atmospheric CO₂ concentration is measured directly and its rate of growth (G_ATM) is computed from the annual changes in concentration. The mean ocean CO₂ sink (S_OCEAN) is based on observations from the 1990s, while the annual anomalies and trends are estimated with ocean models. The variability in S_OCEAN is evaluated with data products based on surveys of ocean CO₂ measurements. The global residual terrestrial CO₂ sink (S_LAND) is estimated by the difference of the other terms of the global carbon budget and compared to results of independent dynamic global vegetation models forced by observed climate, CO₂, and land-cover-change (some including nitrogen–carbon interactions). We compare the mean land and ocean fluxes and their variability to estimates from three atmospheric inverse methods for three broad latitude bands. All uncertainties are reported as ±1σ, reflecting the current capacity to characterise the annual estimates of each component of the global carbon budget. For the last decade available (2004–2013), E_FF was 8.9 ± 0.4 GtC yr⁻¹, E_LUC 0.9 ± 0.5 GtC yr⁻¹, G_ATM 4.3 ± 0.1 GtC yr⁻¹, S_OCEAN 2.6 ± 0.5 GtC yr⁻¹, and S_LAND 2.9 ± 0.8 GtC yr⁻¹. For year 2013 alone, E_FF grew to 9.9 ± 0.5 GtC yr⁻¹, 2.3% above 2012, continuing the growth trend in these emissions, E_LUC was 0.9 ± 0.5 GtC yr⁻¹, G_ATM was 5.4 ± 0.2 GtC yr⁻¹, S_OCEAN was 2.9 ± 0.5 GtC yr⁻¹, and S_LAND was 2.5 ± 0.9 GtC yr⁻¹. G_ATM was high in 2013, reflecting a steady increase in E_FF and smaller and opposite changes between S_OCEAN and S_LAND compared to the past decade (2004–2013). The global atmospheric CO₂ concentration reached 395.31 ± 0.10 ppm averaged over 2013. We estimate that E_FF will increase by 2.5% (1.3–3.5%) to 10.1 ± 0.6 GtC in 2014 (37.0 ± 2.2 GtCO₂ yr⁻¹), 65% above emissions in 1990, based on projections of world gross domestic product and recent changes in the carbon intensity of the global economy. From this projection of E_FF and assumed constant E_LUC for 2014, cumulative emissions of CO₂ will reach about 545 ± 55 GtC (2000 ± 200 GtCO₂) for 1870–2014, about 75% from E_FF and 25% from E_LUC. This paper documents changes in the methods and data sets used in this new carbon budget compared with previous publications of this living data set (Le Quéré et al., 2013, 2014). All observations presented here can be downloaded from the Carbon Dioxide Information Analysis Center (doi:10.3334/CDIAC/GCP_2014).

Abstract:

Refined procedures were developed for directly determining carbonate ion concentrations in seawater through measurement of the ultraviolent absorbances of lead carbonate and chloride complexes after addition of divalent lead (Pb(II)) to a seawater sample. Our model algorithm is based on carbonate ion concentrations calculated from measurements of pH and dissolved inorganic carbon (DIC) obtained on a NOAA ocean acidification cruise (GOMECC-2, the second Gulf of Mexico and East Coast Carbon cruise). These calculated carbonate concentrations, in conjunction with Pb(II) absorbance measurements for the same seawater samples, were used to refine previous algorithms based on different chemical-measurement techniques and a limited range of carbonate concentrations. The precision of the spectrophotometric carbonate measurements is affected by the concentration of Pb(II) in the titrated seawater samples. Doubling the concentration of the titrant improved precision relative to previously published procedures but required formulation of a correction for changes in carbonate ion concentration caused by the titrant addition. Minor changes in the new algorithm for the spectrophotometric method produced carbonate ion values in excellent agreement with values calculated from paired pH and DIC observations over a carbonate concentration range of 73–258 μmol kg^–1. This new algorithm, tested on three subsequent research cruises in the Gulf of Mexico, showed a random scatter of residuals and an average offset between measured and calculated carbonate concentrations equal to –0.92 ± 5.33 μmol kg^–1.

Abstract:

This research assesses the thermodynamic consistency of recent marine CO₂ system measurements in United States coastal waters. As one means of assessment, we compared aragonite saturation states calculated using various combinations of measured parameters. We also compared directly measured and calculated values of total alkalinity and CO₂ fugacity. The primary data set consists of state-of-the-art measurements of the keystone parameters of the marine CO₂ system: dissolved inorganic carbon (DIC), total alkalinity (TA), CO₂ fugacity (fCO₂), and pH. This study is the first thermodynamic CO₂ system intercomparison based on measurements obtained using purified meta cresol purple as a pH indicator. The data are from 1890 water samples collected during NOAA’s West Coast Ocean Acidification Cruise of 2011 (WCOA2011) and NOAA’s Gulf of Mexico and East Coast Carbon Cruise of 2012 (GOMECC-2). Calculations of in situ aragonite saturation states (Ω_A) near the saturation horizon exhibited differences on the order of ±10% between predictions based on the (DIC, TA) pair of measurements versus the (pH, DIC), (fCO₂, DIC), or (fCO₂, pH) pairs. Differences of this magnitude, which are largely attributable to the imprecision of Ω_A calculated from the (DIC, TA) pair, are roughly equivalent to the magnitude of Ω_A change projected to occur over the next several decades due to ocean acidification. These observations highlight the importance of including either pH or fCO₂ in saturation state calculations. Calculations of TA from (pH, DIC) and (fCO₂, DIC) showed that internal consistency could be achieved if minor subtractions of TA (≤ 4 μmol kg⁻¹) were applied to samples of salinity <35. The extent of thermodynamic consistency is also exemplified by the small offset between TA calculated from (DIC, pH) and that calculated from (DIC, fCO₂): ~3 μmol kg⁻¹, which is similar to the accuracy of the TA measurements. Systematic trends can be detected in the offsets between measured and calculated parameters, but for this high quality data set the magnitude of methodological improvements required to achieve exact thermodynamic consistency is quite small.

Abstract:

Global ocean acidification is caused primarily by the ocean’s uptake of CO₂ as a consequence of increasing atmospheric CO₂ levels. We present observations of the oceanic decrease in pH at the basin scale (50°S–36°N) for the Atlantic Ocean over two decades (1993–2013). Changes in pH associated with the uptake of anthropogenic CO₂ (ΔpHCant) and with variations caused by biological activity and ocean circulation (ΔpHNat) are evaluated for different water masses. Output from an Institut Pierre Simon Laplace climate model is used to place the results into a longer-term perspective and to elucidate the mechanisms responsible for pH change. The largest decreases in pH (∆pH) were observed in central, mode, and intermediate waters, with a maximum ΔpH value in South Atlantic Central Waters of −0.042 ± 0.003. The ΔpH trended toward zero in deep and bottom waters. Observations and model results show that pH changes generally are dominated by the anthropogenic component, which accounts for rates between −0.0015 and −0.0020/y in the central waters. The anthropogenic and natural components are of the same order of magnitude and reinforce one another in mode and intermediate waters over the time period. Large negative ΔpHNat values observed in mode and intermediate waters are driven primarily by changes in CO₂ content and are consistent with (i) a poleward shift of the formation region during the positive phase of the Southern Annular Mode in the South Atlantic and (ii) an increase in the rate of the water mass formation in the North Atlantic.

Abstract:

Using measurements of the surface-ocean CO₂ partial pressure (pCO₂) and 14 different pCO₂ mapping methods recently collated by the Surface Ocean pCO₂ Mapping intercomparison (SOCOM) initiative, variations in regional and global sea-air CO₂ fluxes are investigated. Though the available mapping methods use widely different approaches, we find relatively consistent estimates of regional pCO₂ seasonality, in line with previous estimates. In terms of interannual variability (IAV), all mapping methods estimate the largest variations to occur in the eastern equatorial Pacific. Despite considerable spread in the detailed variations, mapping methods that fit the data more closely also tend to agree more closely with each other in regional averages. Encouragingly, this includes mapping methods belonging to complementary types, taking variability either directly from the pCO₂ data or indirectly from driver data via regression. From a weighted ensemble average, we find an IAV amplitude of the global sea-air CO₂ flux of 0.31 PgC yr⁻¹ (standard deviation over 1992-2009), which is larger than simulated by biogeochemical process models. From a decadal perspective, the global ocean CO₂ uptake is estimated to have gradually increased since about 2000, with little decadal change prior to that. The weighted mean net global ocean CO₂ sink estimated by the SOCOM ensemble is −1.75 PgC yr⁻¹ (1992–2009), consistent within uncertainties with estimates from ocean-interior carbon data or atmospheric oxygen trends.

Abstract:

Space-based observations offer unique capabilities for studying spatial and temporal dynamics of the upper ocean inorganic carbon cycle and, in turn, supporting research tied to ocean acidification (OA). Satellite sensors measuring sea surface temperature, color, salinity, wind, waves, currents, and sea level enable a fuller understanding of a range of physical, chemical, and biological phenomena that drive regional OA dynamics, as well as the potentially varied impacts of carbon cycle change on a broad range of ecosystems. Here, we update and expand on previous work that addresses the benefits of space-based assets for OA and carbonate system studies. Carbonate chemistry and the key processes controlling surface ocean OA variability are reviewed. Synthesis of present satellite data streams and their utility in this arena are discussed, as are opportunities on the horizon for using new satellite sensors with increased spectral, temporal, and/or spatial resolution. We outline applications that include the ability to track the biochemically dynamic nature of water masses to map coral reefs at higher resolution, discern functional phytoplankton groups and their relationships to acid perturbations, and track processes that contribute to acid variation near the land-ocean interface.

Abstract:

As part of an effort to monitor changes in inorganic carbon chemistry of the coastal ocean, near-synoptic cruises are being conducted in the northern Gulf of Mexico and along the east coast of the United States. Here we describe observations obtained on a cruise in the summer of 2012 and compare them with results from a cruise following a similar track in 2007. The focus is on describing spatial patterns of aragonite saturation state (Ω_Ar). This parameter is an indicator of ecosystem health, in particular, for calcifying organisms. The results show large-scale regional trends from different source waters at the northeastern and southwestern edges of the domain, along with the modulating effects of remineralization/respiration and riverine inputs. The broader patterns and changes over five years along the coast can be well described by the impacts of large-scale circulation, notably changes in source waters contributions. Changes in the well-buffered Loop Current and Gulf Stream with high Ω_Ar impact the waters in the southern part of the study area. The less buffered southward coastal currents with low Ω_Ar originating from the Labrador Sea and Gulf of St. Lawrence impact the Ω_Ar patterns in the northern regions. The expected 2% average decrease in Ω_Ar in the surface mixed layer due to increasing atmospheric CO₂ levels over the 5-year period is largely overshadowed by local and regional variability from changes in hydrography and mixed layer dynamics.

Abstract:

The subannual variability of total alkalinity (TA) distributions in the northeastern Gulf of Mexico was examined through the use of TA data from ship-based water sampling, historical records of riverine TA, and contemporaneous model output of surface currents and salinity. TA variability was restricted to the upper 150 m of the water column, where relationships between salinity and TA were controlled primarily by subannual variations in the extent of mixing between seawater and river water. A transition in TA distribution patterns between the river-dominated northern margin (near the Mississippi-Atchafalaya River System) and the ocean current-dominated eastern margin (West Florida Shelf) was observed. An index for riverine alkalinity input was formulated to provide insights about riverine alkalinity contributions in the upper water column. Spatial and temporal variations of total alkalinity in the northeastern Gulf of Mexico are primarily controlled by riverine TA inputs and ocean currents.

Abstract:

The Surface Ocean CO₂ Atlas (SOCAT), an activity of the international marine carbon research community, provides access to synthesis and gridded fCO₂ (fugacity of carbon dioxide) products for the surface oceans. Version 2 of SOCAT is an update of the previous release (version 1) with more data (increased from 6.3 million to 10.1 million surface water fCO₂ values) and extended data coverage (from 1968–2007 to 1968–2011). The quality control criteria, while identical in both versions, have been applied more strictly in version 2 than in version 1. The SOCAT website (http://www.socat.info/) has links to quality control comments, metadata, individual data set files, and synthesis and gridded data products. Interactive online tools allow visitors to explore the richness of the data. Applications of SOCAT include process studies, quantification of the ocean carbon sink, and its spatial, seasonal, year-to-year and longer term variation, as well as initialization or validation of ocean carbon models and coupled climate-carbon models.

Abstract:

While the inflow of dissolved inorganic carbon (DIC) from the Pacific Ocean is relatively well quantified, the intermittent input from the East Siberian Sea (ESS) is not. The export flux to the Atlantic Ocean has unknown uncertainty due to a paucity of DIC data from the Canadian Archipelago. Within the region, the Chukchi Sea is the dominant site for atmospheric carbon dioxide (CO₂) uptake, while the Beaufort Sea and the Canadian Archipelago take-up much less CO₂ with latter potentially a weak source of CO₂ during certain times of the year. Additionally, the ESS shelf is a net source of CO₂. Summertime CO₂ uptake capacity in the deep Canada Basin has increased greatly recently as sea-ice retreat progresses rapidly. The region appears to export more DIC than it receives by a small amount, suggesting that it is probably weakly net heterotrophic. In addition to labile organic carbon (OC) produced in the productive marginal seas, some riverine and coastal erosion-derived OC likely is also recycled. As warming progresses, the Arctic Ocean may produce and export more DIC. Whether this change will turn the Arctic Ocean into a weaker CO₂ sink or even a CO₂ source for the atmosphere is uncertain and dependent on multiple factors that control the rate of surface water CO₂ increase versus the rate of the atmospheric CO₂ increase.

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Abstract:

Air-sea CO₂ fluxes over the Pacific Ocean are known to be characterized by coherent large-scale structures that reflect not only ocean subduction and upwelling patterns, but also the combined effects of wind-driven gas exchange and biology. On the largest scales, a large net CO₂ influx into the extratropics is associated with a robust seasonal cycle, and a large net CO₂ efflux from the tropics is associated with substantial interannual variability. In this work, we have synthesized estimates of the net air–sea CO₂ flux from a variety of products, drawing upon a variety of approaches in three sub-basins of the Pacific Ocean, i.e., the North Pacific extratropics (18-66°N), the tropical Pacific (18°S-18°N), and the South Pacific extratropics (44.5-18°S). These approaches include those based on the measurements of CO₂ partial pressure in surface seawater (pCO₂sw), inversions of ocean-interior CO₂ data, forward ocean biogeochemistry models embedded in the ocean general circulation models (OBGCMs), a model with assimilation of pCO₂sw data, and inversions of atmospheric CO₂ measurements. Long-term means, interannual variations and mean seasonal variations of the regionally integrated fluxes were compared in each of the sub-basins over the last two decades, spanning the period from 1990 through 2009. A simple average of the long-term mean fluxes obtained with surface water pCO₂ diagnostics and those obtained with ocean-interior CO₂ inversions are −0.47 ± 0.13 Pg C yr⁻¹ in the North Pacific extratropics, +0.44 ± 0.14 Pg C yr⁻¹ in the tropical Pacific, and −0.37 ± 0.08 Pg C yr⁻¹ in the South Pacific extratropics, where positive fluxes are into the atmosphere. This suggests that approximately half of the CO₂ taken up over the North and South Pacific extratropics is released back to the atmosphere from the tropical Pacific. These estimates of the regional fluxes are also supported by the estimates from OBGCMs after adding the riverine CO₂ flux, i.e., −0.49 ± 0.02 Pg C yr⁻¹ in the North Pacific extratropics, +0.41 ± 0.05 Pg C yr⁻¹ in the tropical Pacific, and −0.39 ± 0.11 Pg C yr⁻¹ in the South Pacific extratropics. The estimates from the atmospheric CO₂ inversions show large variations amongst different inversion systems, but their median fluxes are consistent with the estimates from climatological pCO₂sw data and pCO₂sw diagnostics. In the South Pacific extratropics, where CO₂ variations in the surface and ocean interior are severely undersampled, the difference in the air–sea CO₂ flux estimates between the diagnostic models and ocean-interior CO₂ inversions is larger (0.18 Pg C yr⁻¹). The range of estimates from forward OBGCMs is also large (−0.19 to −0.72 Pg C yr⁻¹). Regarding interannual variability of air–sea CO₂ fluxes, positive and negative anomalies are evident in the tropical Pacific during the cold and warm events of the El Niño-Southern Oscillation in the estimates from pCO₂sw diagnostic models and from OBGCMs. They are consistent in phase with the Southern Oscillation Index, but the peak-to-peak amplitudes tend to be higher in OBGCMs (0.40 ± 0.09 Pg C yr⁻¹) than in the diagnostic models (0.27 ± 0.07 Pg C yr⁻¹).

Abstract:

Warming of abyssal waters in recent decades contributes to global heat uptake and sea level rise. Repeat oceanographic section data in the western South Atlantic taken mostly in 1989 (1995 across the Scotia Sea), 2005, and 2014 are used to quantify warming in abyssal waters that spread northward through the region from their Antarctic origins in the Weddell Sea. While much of the Scotia Sea warmed between 1995 and 2005, only the southernmost portion, on the north side of the Weddell Gyre, continued to warm between 2005 and 2014. The abyssal Argentine Basin also warmed between 1989 and 2005, but again only the southernmost portion continued to warm between 2005 and 2014, suggesting a slowdown in the inflow of the coldest, densest Antarctic Bottom Waters into the western South Atlantic between 1989 and 2014. In contrast, the abyssal waters of the Brazil Basin warmed both between 1989 and 2005 and between 2005 and 2014, at a rate of about 2 m C yr^-1. This warming is also assessed in terms of the rates of change of heights above the bottom for deep isotherms in each deep basin studied. These results, together with findings from previous studies, suggest the deep warming signal observed in the Weddell Sea after the mid-1970s Weddell Polynya was followed by abyssal warming in the Argentine Basin from the late 1970s through about 2005, then warming in the deep Vema Channel from about 1992 through at least 2010, and warming in the Brazil Basin from 1989 to 2014.

Abstract:

Accurate assessment of anthropogenic carbon dioxide (CO₂) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and a methodology to quantify all major components of the global carbon budget, including their uncertainties, based on the combination of a range of data, algorithms, statistics and model estimates and their interpretation by a broad scientific community. We discuss changes compared to previous estimates, consistency within and among components, alongside methodology and data limitations. CO₂ emissions from fossil-fuel combustion and cement production (E_FF) are based on energy statistics, while emissions from land-use change (E_LUC), mainly deforestation, are based on combined evidence from land-cover change data, fire activity associated with deforestation, and models. The global atmospheric CO₂ concentration is measured directly and its rate of growth (G_ATM) is computed from the annual changes in concentration. The mean ocean CO₂ sink (S_OCEAN) is based on observations from the 1990s, while the annual anomalies and trends are estimated with ocean models. The variability in S_OCEAN is evaluated for the first time in this budget with data products based on surveys of ocean CO₂ measurements. The global residual terrestrial CO₂ sink (S_LAND) is estimated by the difference of the other terms of the global carbon budget and compared to results of independent dynamic global vegetation models forced by observed climate, CO₂ and land cover change (some including nitrogen–carbon interactions). All uncertainties are reported as ±1σ, reflecting the current capacity to characterise the annual estimates of each component of the global carbon budget. For the last decade available (2003-2012), E_FF was 8.6 ± 0.4 GtC yr⁻¹, E_LUC 0.9 ± 0.5 GtC yr⁻¹, G_ATM 4.3 ± 0.1 GtC yr⁻¹, S_OCEAN 2.5 ± 0.5 GtC yr⁻¹, and S_LAND 2.8 ± 0.8 GtC yr⁻¹. For year 2012 alone, E_FF grew to 9.7 ± 0.5 GtC yr⁻¹, 2.2% above 2011, reflecting a continued growing trend in these emissions, G_ATM was 5.1 ± 0.2 GtC yr⁻¹, S_OCEAN was 2.9 ± 0.5 GtC yr⁻¹, and assuming an E_LUC of 1.0 ± 0.5 GtC yr⁻¹ (based on the 2001–2010 average), S_LAND was 2.7 ± 0.9 GtC yr⁻¹. G_ATM was high in 2012 compared to the 2003–2012 average, almost entirely reflecting the high E_FF. The global atmospheric CO₂ concentration reached 392.52 ± 0.10 ppm averaged over 2012. We estimate that E_FF will increase by 2.1% (1.1–3.1%) to 9.9 ± 0.5 GtC in 2013, 61% above emissions in 1990, based on projections of world gross domestic product and recent changes in the carbon intensity of the economy. With this projection, cumulative emissions of CO₂ will reach about 535 ± 55 GtC for 1870–2013, about 70% from E_FF (390 ± 20 GtC) and 30% from E_LUC (145 ± 50 GtC). This paper also documents any changes in the methods and data sets used in this new carbon budget from previous budgets (Le Quéré et al., 2013). All observations presented here can be downloaded from the Carbon Dioxide Information Analysis Center (doi:10.3334/CDIAC/GCP_2013_V2.3).

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Abstract:

Here we test the hypothesis that winds have an important role in determining the rate of exchange of CO₂ between the atmosphere and ocean through wind stirring over the Southern Ocean. This is tested with a sensitivity study using an ad hoc parameterization of wind stirring in an ocean carbon cycle model, where the objective is to identify the way in which perturbations to the vertical density structure of the planetary boundary in the ocean impacts the carbon cycle and ocean biogeochemistry. Wind stirring leads to reduced uptake of CO₂ by the Southern Ocean over the period 2000-2006, with a relative reduction with wind stirring on the order of 0.9 Pg C yr⁻¹ over the region south of 45° S. This impacts not only the mean carbon uptake, but also the phasing of the seasonal cycle of carbon and other ocean biogeochemical tracers. Enhanced wind stirring delays the seasonal onset of stratification, and this has large impacts on both entrainment and the biological pump. It is also found that there is a strong reduction on the order of 25-30% in the concentrations of NO₃ exported in Subantarctic Mode Water (SAMW) to wind stirring. This finds expression not only locally over the Southern Ocean, but also over larger scales through the impact on advected nutrients. In summary, the large sensitivity identified with the ad hoc wind stirring parameterization offers support for the importance of wind stirring for global ocean biogeochemistry through its impact over the Southern Ocean.

Abstract:

The relationship between gas exchange and wind speed is used extensively for estimating bulk fluxes of atmospheric gases across the air-sea interface. Here, I provide an update on the frequently used method of Wanninkhof (1992). The update of the methodology reflects advances that have occurred over the past two decades in quantifying the input parameters. The general principle of obtaining a relationship constrained by the globally integrated bomb-¹⁴CO₂ flux into the ocean remains unchanged. The improved relationship is created using revised global ocean ¹⁴C inventories and improved wind speed products. Empirical relationships of the Schmidt number, which are necessary to determine the fluxes, are extended to 40°C to facilitate their use in the models. The focus is on the gas exchange of carbon dioxide, but the suggested functionality can be extended to other gases at intermediate winds (≈4-15 m s^–1). The updated relationship, expressed as k = 0.251 <U²> (Sc/660)^–0.5 where k is the gas transfer velocity, is the average squared wind speed, and Sc is the Schmidt number, has a 20% uncertainty. The relationship is in close agreement with recent parameterizations based on results from gas exchange process studies over the ocean.

Abstract:

With the advent of new sensors and platforms to measure surface water carbon dioxide (CO₂) levels, the dataset quality control (QC) criteria are updated in the Surface Ocean CO₂ Atlas (SOCAT) to accommodate surface water fugacity of CO₂ (fCO_2w) data from these sensors. The current dataset QC flags and their rationale are described. The new sensors and platforms are briefly presented. Some changes in the criteria for assigning dataset QC flags and a new data quality flag are introduced. The term “dataset QC flag” replaces “cruise QC flag” to reflect the alternate platforms that are included in SOCAT. All dataset QC flags will incorporate a specified accuracy of the data. For equilibrator based systems the criteria for equilibrator pressure measurements are relaxed as they are unnecessary stringent for the accuracy of fCO₂ in surface seawater. The acceptable comparison with other in situ data, defined as a high quality cross-over, will meet specific criteria of maximum distance, differences in fCO_2w and sea surface temperature (SST) between two data sets. The scientist submitting the dataset will enter a preliminary dataset flag. Platform type including alternative platforms, such as buoys and self-propelled surface vehicles, will be provided in the metadata and will be available as a selectable option in the Live Access Server (LAS) for SOCAT. These updates facilitate better separation of data of differing origin and quality, and enable incorporation of fCO_2w data from alternative platforms and sensors in SOCAT. The revised criteria will be implemented during quality control for all new and updated data sets in version 3 onwards, but not to data sets already in versions 1 or 2. To view recommendations the reader should peruse section 6. The updated criteria for dataset QC flags are in Table 3.

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Abstract:

An autonomous system using isotope dilution as its core method has been developed to obtain high-frequency measurements of dissolved inorganic carbon (DIC) concentrations in the surface ocean. This system accurately mixes a seawater sample and a ¹³C-labeled sodium bicarbonate solution (spike). The mixed solution is then acidified and sent through a gas permeable membrane contactor. CO₂ derived from DIC in the mixture is extracted by a CO₂-free gas stream and is sent to a cavity ring-down spectrometer to analyze its ¹³C/¹²C ratio. [DIC] of the seawater can then be derived from the measured ¹³C/¹²C, the known mixing ratio and the [DI¹³C] of the spike. The method has been tested under a wide [DIC] range (1800-2300 µmol/kg) in the laboratory. It has also been deployed on a cruise that surveyed ocean waters to the south of Florida. At a sampling resolution of 4 min (15 samples per hour), the relative standard deviation of DIC determined from the laboratory tests and the field deployment is ±0.07% and ±0.09%, respectively. The accuracy of the method is better than 0.1% except where [DIC] varies faster than 5 µmol/kg per minute. Based on the laboratory and field evaluations, we conclude that this method can provide accurate underway [DIC] measurements at high resolution in most oceanic regions.

Abstract:

A well-documented, publicly available global data set of surface ocean carbon dioxide (CO₂) parameters has been called for by international groups for nearly two decades. The Surface Ocean CO₂ Atlas (SOCAT) project was initiated by the international marine carbon science community in 2007 with the aim of providing a comprehensive, publicly available, regularly updated, global data set of marine surface CO₂, which had been subject to quality control (QC). Many additional CO₂ data, not yet made public via the Carbon Dioxide Information Analysis Center (CDIAC), were retrieved from data originators, public websites, and other data centers. All data were put in a uniform format following a strict protocol. Quality control was carried out according to clearly-defined criteria. Regional specialists performed the quality control, using state-of-the-art web-based tools, specially developed for accomplishing this global team effort. SOCAT version 1.5 was made public in September 2011 and holds 6.3 million quality controlled surface CO₂ data points from the global oceans and coastal seas, spanning four decades (1968-2007). Three types of data products are available: individual cruise files, a merged complete data set, and gridded products. With the rapid expansion of marine CO₂ data collection and the importance of quantifying net global oceanic CO₂ uptake and its changes, sustained data synthesis and data access are priorities.

Abstract: The Atlantic and Arctic oceans are critical components of the global carbon cycle. Here we quantify the net sea-air CO₂ flux, for the first time, across different methodologies for consistent time and space scales, for the Atlantic and Arctic basins. We present the long-term mean, seasonal cycle, interannual variability, and trends in sea-air CO₂ flux for the period 1990 to 2009, and assign an uncertainty to each. We use regional cuts from global observations and modelling products, specifically a pCO₂-based CO₂ flux climatology, flux estimates from the inversion of oceanic and atmospheric data, and results from six ocean biogeochemical models. Additionally, we use basin-wide flux estimates from surface ocean pCO₂ observations based on two distinct methodologies. Our best estimate of the contemporary sea-to-air flux of CO₂ (sum of anthropogenic and natural components) by the Atlantic between 40°S and 79°N is -0.49 ± 0.11 Pg C yr^-1 and by the Arctic is -0.12 ± 0.06 Pg C yr^-1, leading to a combined sea-to-air flux of -0.61 ± 0.12 Pg C yr^-1 for the two decades (negative reflects ocean uptake). We do find broad agreement amongst methodologies with respect to the seasonal cycle in the subtropics of both hemispheres, but not elsewhere. Agreement with respect to detailed signals of interannual variability is poor; and correlations to the North Atlantic Oscillation are weaker in the North Atlantic and Arctic than in the equatorial region and South Subtropics. Linear trends for 1995 to 2009 indicate increased uptake and generally correspond between methodologies in the North Atlantic, but there is disagreement amongst methodologies in the equatorial region and south subtropics.

Abstract:

Distributions of total alkalinity (TA), dissolved inorganic carbon (DIC), and other parameters relevant to the marine inorganic carbon system were investigated in shelf and adjacent ocean waters during a U.S. Gulf of Mexico and East Coast Carbon cruise in July-August 2007. TA exhibited near-conservative behavior with respect to salinity. Shelf concentrations were generally high in southern waters (Gulf of Mexico and east Florida) and decreased northward from Georgia to the Gulf of Maine. DIC was less variable geographically and exhibited strongly nonconservative behavior. As a result, the ratio of TA to DIC generally decreased northward. The spatial patterns of other CO₂ system parameters closely followed those of the TA:DIC ratio. All sampled shelf waters were supersaturated with respect to aragonite (saturation state Ω_A > 1). The most intensely buffered and supersaturated waters (Ω_A > 5.0) were in northern Gulf of Mexico river-plume waters; the least intensely buffered and least supersaturated waters (Ω_A < 1.3) were in the deep Gulf of Maine. Due to their relatively low pH, Ω_A, and buffer intensity, waters of the northeastern U.S. shelves may be more susceptible to acidification pressures than are their southern counterparts. In the Mid-Atlantic Bight, alongshore mixing tended to increase DIC concentrations southward, but this effect was largely offset by the opposing effects of biogeochemical processing. In the Gulf of Mexico, downstream increases in Loop Current DIC suggested significant contributions from shelf and gulf waters, estimated at 9.1 x 10⁹ mol C d^-1. Off the southeastern U.S., along-flow chemical changes in the Florida Current were dominated by mixing associated with North Atlantic subtropical recirculation.

Abstract: The globally integrated sea-air anthropogenic carbon dioxide (CO₂) flux from 1990 to 2009 is determined from models and data-based approaches as part of the Regional Carbon Cycle Assessment and Processes (RECCAP) project. Numerical methods include ocean inverse models, atmospheric inverse models, and ocean general circulation models with parameterized biogeochemistry (OBGCMs). The median value of different approaches shows good agreement in average uptake. The best estimate of anthropogenic CO₂ uptake for the time period based on a compilation of approaches is 2.0 Pg C yr^-1. The interannual variability in the sea-air flux is largely driven by large-scale climate reorganizations and is estimated at 0.2 Pg C yr^-1 for the two decades with some systematic differences between approaches. The largest differences between approaches are seen in the decadal trends. The trends range from -0.13 (Pg C yr^-1) decade^-1 to 0.50 (Pg C yr^-1) decade^-1 for the two decades under investigation. The OBGCMs and the databased sea-air CO₂ flux estimates show appreciably smaller decadal trends than estimates based on changes in carbon inventory, suggesting that methods capable of resolving shorter timescales are showing a slowing of the rate of ocean CO₂ uptake. RECCAP model outputs for five decades show similar differences in trends between approaches.

Abstract: Detection and attribution of hydrographic and biogeochemical changes in the deep ocean are challenging due to the small magnitude of their signals and to limitations in the accuracy of available data. However, there are indications that anthropogenic and climate change signals are starting to manifest at depth. The deep ocean below 2000 m comprises about 50% of the total ocean volume, and changes in the deep ocean should be followed over time to accurately assess the partitioning of anthropogenic carbon dioxide (CO₂) between the ocean, terrestrial biosphere, and atmosphere. Here we determine the changes in the interior deep-water inorganic carbon content by a novel means that uses the partial pressure of CO₂ measured at 20°C, pCO₂(20), along three meridional transects in the Atlantic and Pacific oceans. These changes are measured on decadal time scales using observations from the World Ocean Circulation Experiment (WOCE)/World Hydrographic Program (WHP) of the 1980s and 1990s and the CLIVAR/CO₂ Repeat Hydrography Program of the past decade. The pCO₂(20) values show a consistent increase in deep water over the time period. Changes in total dissolved inorganic carbon (DIC) content in the deep interior are not significant or consistent, as most of the signal is below the level of analytical uncertainty. Using an approximate relationship between pCO₂(20) and DIC change, we infer DIC changes that are at the margin of detectability. However, when integrated on the basin scale, the increases range from 8-40% of the total specific water column changes over the past several decades. Patterns in chlorofluorocarbons (CFCs), along with output from an ocean model, suggest that the changes in pCO₂(20) and DIC are of anthropogenic origin.

Abstract:

Based on measurements from the WOCE/JGOFS global CO₂ survey, the CLIVAR/CO₂ Repeat Hydrography Program and the Canadian Line P survey, we have observed an average decrease of 0.34% yr^-1 in the saturation state of surface seawater in the Pacific Ocean with respect to aragonite and calcite. The upward migrations of the aragonite and calcite saturation horizons, averaging about 1 to 2 m yr^-1, are the direct result of the uptake of anthropogenic CO₂ by the oceans and regional changes in circulation and biogeochemical processes. The shoaling of the saturation horizon is regionally variable, with more rapid shoaling in the South Pacific where there is a larger uptake of anthropogenic CO₂. In some locations, particularly in the North Pacific Subtropical Gyre and in the California Current, the decadal changes in circulation can be the dominant factor in controlling the migration of the saturation horizon. If CO₂ emissions continue as projected over the rest of this century, the resulting changes in the marine carbonate system would mean that many coral reef systems in the Pacific would no longer be able to sustain a sufficiently high rate of calcification to maintain the viability of these ecosystems as a whole, and these changes perhaps could seriously impact the thousands of marine species that depend on them for survival.

Abstract:

The deep ocean plays a crucial role in aspects of the climate system on longer time-scales including the global heat budget, sea level rise, potential variations in the meridional overturning circulation, and long-term storage of climatically-relevant compounds such as CO₂, among others. Expanding the ocean observing system towards being truly global will include adequately measuring the half of the ocean volume below 2000 m depth. This will require an increased commitment to the design and implementation of technologies for collecting deep ocean data and transmitting these data to shore in a cost-effective manner. This paper (based on the CWP of the same title) focuses on four of the fundamental areas where improvements to the observing system in the deep ocean are critical to the advancement of our understanding of climate science. These include deep circulation with an emphasis on "strong flows," ocean heat content, fresh water/salinity content, and CO₂ content. It is clear that to continue working towards understanding of climate variations and their impact on society, it is imperative to maintain existing observing systems while improving and expanding the deep ocean components of the Global Ocean Observing System. Recommendations are provided for expanding the observing systems for deep circulation, for deep temperature and salinity variations (hence heat and fresh water estimates), and for deep observations of CO₂ and other chemical tracers. Recommendations are also provided in areas where technological advances are required to improve the ability to collect this data remotely using either free-floating or fixed observing platforms.

Abstract:

Determining a robust trend of surface ocean carbon dioxide (CO₂) for a period shorter than a decade is challenging due to large seasonal variability and a sparsity of data. Here, we estimate the multiannual trend of surface CO₂ in the region of 19°N-20°N, 65°W-68°W for the period of 2002-2009. We used an unprecedented number of high-quality underway data of the fugacity of CO₂ in surface seawater (fCO_2SW) collected from 137 cruises using an automated system onboard the cruise ship Explorer of the Seas. The growth rate of fCO_2SW was estimated by two de-seasonalization approaches that showed similar and significantly lower values than the atmospheric increases, leading to a large increase in the CO₂ sink. The seasonal difference in the trends was significant, with fCO_2SW values in winter showing no increase, while summer fCO_2SW values lagged only slightly with the atmosphere. We attribute the lack of an increase in winter fCO_2SW values to sea surface temperature changes, which are closely correlated with the El Niño-Southern Oscillation cycle, and to changes in the mixed layer depth. The slower increase of fCO_2SW is also related to decreases in salinity. The 8-year averaged annual net sea-air CO₂ flux was -0.06 ± 0.18 mol m^-2 yr^-1 compared to a climatology that shows a flux out of the ocean of +0.11 mol m^-2 yr^-1. The increasing flux differs from previous, mostly longer-term results for regional studies and time series stations in the North Atlantic, which suggests a decrease or no change in oceanic CO₂ uptake.

Abstract:

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Abstract:

The global ocean is undergoing fundamental and rapid changes in response to warming, changes in wind stress, atmospheric CO₂ increases, and changes in the hydrologic cycle. Each of these factors has impacts on the ocean carbon cycle and the ability of the ocean to sequester CO₂ from the atmospheric. In turn, changes in the ocean carbon cycle, and ocean warming and stratification, lead to changes in ocean biogeochemistry and ecology. Feedbacks and impacts are complex and not fully understood. However, rapid advances in observing system technology are occurring, along with improvements in models and understanding of the system. A comprehensive integrated ocean carbon observing system (IOCOS) to understand and monitor these changes is within reach in the next decade. Rather than relying on a single approach or parameter, the IOCOS will be composed of an integrated system of ongoing surface and subsurface observations, modeling, and assessments. This observing element will also rely heavily on other parts of the International Ocean Observing System (IOOS). It will include new technology and modeling approaches to quantify carbon fluxes and inventories in the world’s oceans.

Abstract:

CARIOCA drifters and ship data from several cruises in the Subantarctic Zone (SAZ) of the Pacific Ocean, approximately 40°S-55°S, have been used in order to investigate surface CO₂ partial pressure (pCO₂) and dissolved inorganic carbon (DIC) patterns. The highest DIC values were determined in regions of deep water formation, characterized by deep mixed layer depths (MLD) as estimated from Argo float profiles. As a result, these areas act as sources of CO₂ to the atmosphere. Using an empirical linear relationship between DIC, sea surface temperature (SST), and MLD, we then combine DIC with AT based on salinity and compute pCO₂. Finally, we derive monthly fields of air-sea CO₂ flux in the SAZ. Our fit predicts the existence of a realistic seasonal cycle, close to equilibrium with the atmosphere in winter and a sink when biological activity takes place. It also reproduces the impact that deep water formation regions close to the Subantarctic Front (SAF) and in the eastern part of the SAZ have on the uptake capacity of the area. These areas, undersampled in previous studies, have high pCO₂, and as a result, our estimates (0.05 - 0.03 PgC yr^-1) indicate that the Pacific SAZ acts as a weaker sink of CO₂ than suggested by previous studies which neglect these source regions.

Abstract:

Sea-air fluxes of gases are commonly calculated from the product of the gas transfer velocity (k) and the departure of the seawater concentration from atmospheric equilibrium. Gas transfer velocities, generally parameterized in terms of wind speed, continue to have considerable uncertainties, partly because of limited field data. Here we evaluate commonly used gas transfer parameterizations using a historical data set of ²²²Rn measurements at 105 stations occupied on Eltanin cruises and the Geosecs program. We make this evaluation with wind speed estimates from meteorological reanalysis products (from National Centers for Environmental Prediction and European Centre for Medium-Range Weather Forecasting) that were not available when the ²²²Rn data were originally published. We calculate gas transfer velocities from the parameterizations by taking into account winds in the period prior to the date that ²²²Rn profiles were sampled. Invoking prior wind speed histories leads to much better agreement than simply calculating parameterized gas transfer velocities from wind speeds on the day of sample collection. For individual samples from the Atlantic Ocean, where reanalyzed winds agree best with observations, three similar recent parameterizations give k values for individual stations with an rms difference of ~40% from values calculated using ²²²Rn data. Agreement of basin averages is much better. For the global data set, the average difference between k constrained by ²²²Rn and calculated from the various parameterizations ranges from -0.2 to +0.9 m/d (average, 2.9 m/d). Averaging over large domains, and working with gas data collected in recent years when reanalyzed winds are more accurate, will further decrease the uncertainties in sea-air fluxes.

Abstract: A common approach for estimating the oceanic uptake of anthropogenic carbon dioxide (C_anthro) depends on the linear approximation of oceanic dissolved inorganic carbon (DIC) from a suite of physical and biological ocean parameters. The extended multiple linear regression (eMLR) method assumes that baseline correlations and the resulting residual fields will remain constant with time even under the influence of secular climate changes. The validity of these assumptions over the 21st century is tested using a coupled carbon-climate model. Findings demonstrate that the influence of both changing climate and changing chemistry beyond 2-4 decades invalidates the assumption that the residual fields will remain constant resulting in significant errors in the eMLR estimate of Canthro. This study determines that the eMLR method is unable to describe C_anthro uptake for a sampling interval of greater than 30 years if the error is to remain below 20% for many regions in the Southern Ocean, Atlantic Ocean, and western Pacific Ocean. These results suggest that, for many regions of the ocean basins, hydrographic field investigations have to be repeated at approximately decadal timescales in order to accurately predict the uptake of C_anthro by the ocean if the eMLR method is used.

Abstract:

The Southern Ocean Gas Exchange Experiment (SO GasEx) is the third in a series of U.S.-led open ocean process studies aimed at improving the quantification of gas transfer velocities and air-sea CO₂ fluxes. Two deliberate ³He/SF₆ tracer releases into relatively stable water masses selected for large ΔpCO₂ took place in the southwest Atlantic sector of the Southern Ocean in austral fall of 2008. The tracer patches were sampled in a Lagrangian manner, using observations from discrete CTD/Rosette casts, continuous surface ocean and atmospheric monitoring, and autonomous drifting instruments to study the evolution of chemical and biological properties over the course of the experiment. CO₂ and DMS fluxes were directly measured in the marine air boundary layer with micrometeorological techniques, and physical, chemical, and biological processes controlling air-sea fluxes were quantified with measurements in the upper ocean and marine air. Average wind speeds of 9 m s^-1 to a maximum of 16 m s^-1 were encountered during the tracer patch observations, providing additional data to constrain wind speed/gas exchange parameterizations. In this paper, we set the stage for the experiment by detailing the hydrographic observations during the site surveys and tracer patch occupations that form the underpinning of observations presented in the SO GasEx special section. Particular consideration is given to the mixed layer depth as this is a critical variable for estimates of fluxes and biogeochemical transformations based on mixed layer budgets.

Abstract:

Two ³He/SF₆ dual-gas tracer injections were conducted during the Southern Ocean Gas Exchange Experiment (SO GasEx) to determine gas transfer velocities. During the experiment, wind speeds of up to 16.4 m s^-1 were encountered. A total of 360 ³He and 598 SF₆ samples were collected at 40 conductivity-temperature-depth (CTD) rosette casts and two pumped stations. The gas transfer velocity k was calculated from the decrease in the observed ³He/SF₆ ratio using three different approaches. Discrete points of wind speed and corresponding k were obtained from the change in ³He/SF₆ ratio over three time intervals. The results were also evaluated using an analytical model and a 1-D numerical model. The results from the three approaches agreed within the error of the estimates of about ±13%±15% for Patch 1 and ±4% for Patch 2. Moreover, ³He/SF₆ dual-tracer results from SO GasEx are similar to those from other areas in both the coastal and open ocean and are in agreement with existing parameterizations between wind speed and gas exchange. This suggests that wind forcing is the major driver of gas exchange for slightly soluble gases in the ocean and that other known impacts are either intrinsically related to wind or have a small effect (<20% on average) on time scales of the order of days to weeks. The functionality of the wind speed dependence (quadratic or cubic) cannot be unequivocally determined from SO GasEx results.

Abstract: The North Atlantic Ocean accounts for about 25% of the global oceanic anthropogenic carbon sink. This basin experiences significant interannual variability primarily driven by the North Atlantic Oscillation (NAO). A suite of biogeochemical model simulations is used to analyze the impact of interannual variability on the uptake and storage of contemporary and anthropogenic carbon (C_anthro) in the North Atlantic Ocean. Greater winter mixing during positive NAO years results in increased mode water formation and subsequent increases in subtropical and subpolar C_anthro inventories. Our analysis suggests that changes in mode water C_anthro inventories are primarily due to changes in water mass volumes driven by variations in water mass transformation rates rather than local air-sea CO₂ exchange. This suggests that a significant portion of anthropogenic carbon found in the ocean interior may be derived from surface waters advected into water formation regions rather than from local gas exchange. Therefore, changes in climate modes, such as the NAO, may alter the residence time of anthropogenic carbon in the ocean by altering the rate of water mass transformation. In addition, interannual variability in C_anthro storage increases the difficulty of C_anthro detection and attribution through hydrographic observations, which are limited by sparse sampling of subsurface waters in time and space.

Abstract: No abstract.

Abstract:

This report details the measurement of oxygen (O₂) by the Winkler method on the ships Nancy Foster, Ocean Veritas, Brooks McCall, Henry B. Bigelow, and Pisces in response to the oil spill of the Deepwater Horizon 252 well. Most of the data are from near the well and were obtained from July 1, 2010 to August 30, 2010. The purpose of these measurements was to assess the accuracy of the oxygen sensors on a conductivity-temperature-depth (CTD) sensor, henceforth referred to as CTD/O₂, and to determine if the CTD/O₂ sensor provided (low) biased readings in the presence of oil. Based on the analyses, we believe that the O₂ analyses from the CTD/O₂ and Winkler systems on the ships were accurate to within 2% (approximately equal to 4 µmol/l, approximately equal to 0.1 ml/l, or approximately equal to 0.15 ml/l), with exceptions listed in the following paragraph. The depression in O₂ values observed by the CTD/O₂ at depths of 1000-1300 m in the layer with diffuse oil were verified by the Winkler measurements and are attributed to oxidation of the oil and associated gas. Based on the Winkler measurements, we cannot conclusively recommend adjustments to the CTD/O₂ data. A qualitative assessment suggests that the output of CTD/O₂ sensors on the Brooks McCall and Ocean Veritas agreed with each other and with the Winkler measurements to within 2%. The CTD/O₂ sensor on the Pisces appeared to read low by about 3% when compared with the Henry B. Bigelow CTD/O₂ and Winkler O₂ values that agreed well with each other. The Nancy Foster had the largest dataset of Winkler O₂ values for comparison. These values were about 2.6 ± 2% higher than the CTD/O₂ values in water depths of 100-1000 m but showed larger positive deviations of up to 10% at the surface and in deep water which we cannot explain.

Abstract:

Global air-sea CO₂ fluxes are commonly determined using the CO₂ partial pressure difference between surface water and air (DELTApCO₂), and wind speed. Numerical interpolation techniques and coarse grid spacing, typically of the order of 4°, used when estimating the global fluxes smooth out small-scale variability in wind and pCO₂ fields. There is significant variability on smaller scales in these fields. In particular, wind speed is strongly affected by sea surface temperature (SST) on oceanic mesoscales. Here we provide an estimate of the impact of this small-scale variability on global CO₂ fluxes utilizing a highresolution wind product, and estimates of surface water CO₂ changes in response to small-scale changes in SST. The results show that, on a global scale, the annual air-sea CO₂ fluxes for 1° smoothed fields is 2 to 4% greater than for 10° smoothed SST and winds fields. This suggests that, while the coarser resolution fields used in climatologies miss much of the small-to-regional scale variability in fluxes, they adequately present global and basin-scale flux estimates.

Abstract: Coastal environments are an important component of the global carbon cycle, and probably more vulnerable than the open ocean to anthropogenic forcings. Due to strong spatial heterogeneity and temporal variability, carbon flows in coastal environments are poorly constrained. Hence, an integrated, international, and interdisciplinary program of ship-based hydrography, Voluntary Observing Ship (VOS) lines, time-series moorings, floats, gliders, and autonomous surface vessels with sensors for pCO₂ and ancillary variables are recommended to better understand present day carbon cycle dynamics, quantify air-sea CO₂ fluxes, and determine future long-term trends of CO₂ in response to global change forcings (changes in river inputs, in the hydrological cycle, in circulation, sea-ice retreat, expanding oxygen minimum zones, ocean acidification, etc.) in the coastal oceans. Integration at the international level is also required for data archiving, management, and synthesis that will require multi-scale approaches including the development of biogeochemical models and use of remotely sensed parameters. The total cost of these observational efforts is estimated at about 50 million U.S. dollars per year.

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Abstract:

We observed O₂ deficits of 0.5 to 2.0% (1 to 4 µmol/kg) in the underway seawater lines of three different ships. Deficits in O₂/Ar and isotopic enrichments in dissolved O₂ observed in underway seawater lines indicate a respiratory removal process. A 1% respiratory bias in underway lines would lead to a 2.5-5 µatm (2.5-5 µbar) enhancement in surface water pCO₂. If an underway pCO₂ bias of this magnitude affected all measurements, the global oceanic carbon uptake based on pCO₂ climatologies would be 0.5-0.8 Pg/yr higher than the present estimate of 1.6 Pg/yr. Treatment of underway lines with bleach for several hours and thorough flushing appeared to minimize O₂ loss. Given the increasing interest in underway seawater measurements for the determination of surface CO₂ and O₂ fluxes, respiration in underway seawater lines must be identified and eliminated on all observing ships to ensure unbiased data.

Abstract:

This paper presents the results of two cruises in the northern Gulf of Mexico in 2008 that investigated local and short-term factors influencing the carbonate chemistry dynamics and saturation state with respect to aragonite (Ω_aragonite) of surface seawater in this region. One cruise covered much of the northern half of the Gulf, and the other focused on the coastal zone west of the Atchafalaya Bay outlet of the Mississippi River--the region where the hypoxic dead zone occurs on the Louisiana shelf. Offshore waters (>100 m depth) exhibited only small variations in CO₂ fugacity (fCO₂), total alkalinity (TA), and Ω_aragonite. Values were close to those typically observed in subtropical Atlantic Ocean and Caribbean Sea waters of similar salinity. However, inner shelf waters (2, TA, and Ω_aragonite that were not directly related to salinity or distance from the Mississippi River plume. Changes in TA values were not the result of simple mixing of end-member freshwater and seawater TA concentrations but exhibited a minimum in values near salinity of 25. This minimum could be the result of microbial recycling across salinity gradients, biological removal of alkalinity by formation of calcium carbonate or mixing of a third end-member with a low alkalinity such as Terrebonne Bay. All waters were supersaturated with respect to aragonite. Offshore waters had an average Ω_aragoniteof 3.86 with a standard deviation of only ±0.06 and inner shelf waters had a range in Ω_aragonite values from 3.9 to 9.7 with a median of 4.3. Shelf water Ω_aragonite values were elevated relative to the offshore as a consequence of both high TA input from Mississippi River and biological drawdown of CO₂. A dominant factor controlling Ω_aragonite distribution in offshore waters with relatively constant temperatures was fCO₂, with higher supersaturation occurring in areas with low fCO₂.

Abstract:

Recent studies based on ocean and atmospheric carbon dioxide (CO₂) observations, suggesting that the ocean carbon uptake has been reduced, may help explain the increase in the fraction of anthropogenic CO₂ emissions that remain in the atmosphere. Is it a response to climate change or a signal of ocean natural variability or both? Regional process analyses are needed to follow the ocean carbon uptake and to enable better attributions of the observed changes. Here, we describe the evolution of the surface ocean CO₂fugacity (fCO₂^oc) over the period 1993–2008 in the North Atlantic subpolar gyre (NASPG). This analysis is based primarily on observations of dissolved inorganic carbon (DIC) and total alkalinity (TA) conducted at different seasons in the NASPG between Iceland and Canada. The fCO₂^oc trends based on DIC and TA data are also compared with direct fCO₂ measurements obtained between 2003 and 2007 in the same region. During winters 1993–2003, the fCO₂^oc growth rate was 3.7 (±0.6) μatm yr⁻¹, higher than in the atmosphere, 1.8 (±0.1) μatm yr⁻¹. This translates to a reduction of the ocean carbon uptake primarily explained by sea surface warming, up to 0.24 (±0.04) °C yr⁻¹. This warming is a consequence of advection of warm water northward from the North Atlantic into the Irminger basin, which occurred as the North Atlantic Oscillation (NAO) index moved into a negative phase in winter 1995/1996. In winter 2001–2008, the fCO₂^oc rise was particularly fast, between 5.8 (±1.1) and 7.2 (±1.3) μatm yr⁻¹ depending on the region, more than twice the atmospheric growth rate of 2.1 (±0.2) μatm yr⁻¹, and in the winter of 2007–2008 the area was supersaturated with CO₂. As opposed to the 1990s, this appears to be almost entirely due to changes in seawater carbonate chemistry, the combination of increasing DIC and decreasing of TA. The rapidfCO₂^oc increase was not only driven by regional uptake of anthropogenic CO₂ but was also likely controlled by a recent increase in convective processes-vertical mixing in the NASPG and cannot be directly associated with NAO variability. The fCO₂^oc increase observed in 2001–2008 leads to a significant drop in pH of −0.069 (±0.007) decade⁻¹.

Abstract: No abstract.

Abstract:

Seasonal air-sea carbon dioxide (CO₂) flux maps were calculated from wind speed data and the difference in CO₂ partial pressure between surface seawater (pCO_2SW) and the overlying atmosphere. To infer the seasonal variability of global net air-sea CO₂ fluxes over the last three decades, we derived the optimum subannual relationships between pCO_2SW and the sea surface temperature (SST). These optimum subannual relationships accounted for the variations between pCO_2SW and SST and showed significantly better correlations than previous relationships with fixed monthly boundaries. The derived algorithms were then applied to high-resolution SST data to yield changes in pCO_2SW on a monthly basis. The pCO_2SW values were also combined with a gas transfer velocity estimate derived from high resolution wind products to estimate seasonal fluxes. The seasonal fluxes that are calculated with a three- to six-month lag from real-time can be obtained at http://cwcgom.aoml.noaa.gov/erddap/griddap/aomlcarbonfluxes.graph. Here, we describe in detail the procedures and uncertainties of this product.

Abstract:

The interannual variability of net sea–air CO₂ flux for the period 1982–2007 is obtained from a diagnostic model using empirical subannual relationships between climatological CO₂ partial pressure in surface seawater (pCO_2SW) and sea surface temperature (SST), along with interannual changes in SST and wind speed. These optimum subannual relationships show significantly better correlation between pCO_2SW and SST than the previous relationships using fixed monthly boundaries. Our diagnostic model yields an interannual variability of ±0.14 PgC yr⁻¹ (1σ) with a 26-year mean of −1.48 PgC yr⁻¹. The greatest interannual variability is found in the Equatorial Pacific, and significant variability is also found at northern and southern high-latitudes, depending in part, on which wind product is used. We provide an assessment of our approach by applying it to pCO_2SW and SST output from a prognostic global biogeochemical ocean model. Our diagnostic approach applied to this model output shows reasonable agreement with the prognostic model net sea–air CO₂fluxes in terms of magnitude and phase of variability, suggesting that our diagnostic approach can capture much of the observed variability on regional to global scale. A notable exception is that our approach shows significantly less variability than the prognostic model in the Southern Ocean.

Abstract: Data from the first systematic survey of inorganic carbon parameters on a global scale, the GEOSECS program, are compared with those collected during WOCE/JGOFS to study the changes in carbon and other geochemical properties, and anthropogenic CO₂ increase in the Atlantic Ocean from the 1970s to the early 1990s. This first data-based estimate of CO₂ increase over this period was accomplished by adjusting the GEOSECS data set to be consistent with recent high-quality carbon data. Multiple Linear Regression (MLR) and extended Multiple Linear Regression (eMLR) analyses to these carbon data are applied by regressing DIC with potential temperature, salinity, AOU, silica, and PO₄ in three latitudinal regions for the western and eastern basins in the Atlantic Ocean. The results from MLR (and eMLR provided in parentheses) indicate that the mean anthropogenic CO₂ uptake rate in the western basin is 0.70 (0.53) mol m^-2 yr^-1 for the region north of 151°N; 0.53 (0.36) mol m^-2 yr^-1 for the equatorial region between 151°N and 151°S; and 0.83 (0.35) mol m^-2 yr^-1 in the South Atlantic south of 151°S. For the eastern basin an estimate of 0.57 (0.45) m^-2 yr^-1 is obtained for the equatorial region, and 0.28 (0.34) mol m^-2 yr^-1 for the South Atlantic south of 151°S. The results of using eMLR are systematically lower than those from MLR method in the western basin. The anthropogenic CO₂ increase is also estimated in the upper thermocline from salinity normalized DIC after correction for AOU along the isopycnal surfaces. For these depths the results are consistent with the CO₂ uptake rates derived from both MLR and eMLR methods.

Abstract: Water column data of carbon and carbon-relevant hydrographic and hydrochemical parameters from 188 cruises in the Arctic Mediterranean Seas, Atlantic and Southern Ocean have been retrieved and merged in a new data base: the CARINA (CARbon IN the Atlantic) Project. These data have gone through rigorous quality control (QC) procedures so as to improve the quality and consistency of the data as much as possible. Secondary quality control, which involved objective study of data in order to quantify systematic differences in the reported values, was performed for the pertinent parameters in the CARINA data base. Systematic biases in the data have been tentatively corrected in the data products. The products are three merged data files with measured, adjusted and interpolated data of all cruises for each of the three CARINA regions (Arctic Mediterranean Seas, Atlantic and Southern Ocean). Ninety-eight cruises were conducted in the Atlantic defined as the region south of the Greenland-Iceland-Scotland Ridge and north of about 30°S. Here we report the details of the secondary QC which was done on the total dissolved inorganic carbon (TCO₂) data and the adjustments that were applied to yield the final data product in the Atlantic. Procedures of quality control, including crossover analysis between stations and inversion analysis of all crossover data, are briefly described. Adjustments were applied to TCO₂ measurements for 17 of the cruises in the Atlantic Ocean region. With these adjustments, the CARINA database is consistent both internally as well as with GLODAP data, an oceanographic data set based on the WOCE Hydrographic Program in the 1990s, and is now suitable for accurate assessments of, for example, regional oceanic carbon inventories, uptake rates, and model validation.

Abstract:

No abstract.

Abstract: Water column data of carbon and carbon-relevant hydrographic and hydrochemical parameters from 188 previously non-publicly available cruise data sets in the Arctic Mediterranean Seas, Atlantic and Southern Ocean have been retrieved and merged into a new database: CARINA (CARbon dioxide IN the Atlantic Ocean). The data have gone through rigorous quality control procedures to assure the highest possible quality and consistency. The data for the pertinent parameters in the CARINA database were objectively examined in order to quantify systematic differences in the reported values, i.e., secondary quality control. Systematic biases found in the data have been corrected in the three data products: merged data files with measured, calculated, and interpolated data for each of the three CARINA regions, i.e., the Arctic Mediterranean Seas, the Atlantic and the Southern Ocean. These products have been corrected to be internally consistent. Ninety-eight of the cruises in the CARINA database were conducted in the Atlantic Ocean, defined here as the region south of the Greenland-Iceland-Scotland Ridge and north of about 30°S. Here we present an overview of the Atlantic Ocean synthesis of the CARINA data and the adjustments that were applied to the data product. We also report the details of the secondary QC (Quality Control) for salinity for this data set. Procedures of quality control, including crossover analysis between stations and inversion analysis of all crossover data, are briefly described. Adjustments to salinity measurements were applied to the data from 10 cruises in the Atlantic Ocean region. Based on our analysis we estimate the internal consistency of the CARINA-ATL salinity data to be 4.1 ppm. With these adjustments the CARINA data products are consistent both internally as well as with GLODAP data, an oceanographic data set based on the World Hydrographic Program in the 1990s, and is now suitable for accurate assessments of, for example, oceanic carbon inventories and uptake rates and for model validation.

Abstract:

Repeat observations along the meridional Atlantic section A16 from Iceland to 56°S show substantial changes in the total dissolved inorganic carbon (DIC) concentrations in the ocean between occupations from 1989 through 2005. The changes correspond to the expected increase in DIC driven by the uptake of anthropogenic CO₂ from the atmosphere, but the Δ-DIC is more varied and larger, in some locations, than can be explained solely by this process. Concomitant large changes in oxygen (O₂) suggest that processes acting on the natural carbon cycle also contribute to Δ-DIC. Precise partial pressure of CO₂ measurements suggest small but systematic increases in the bottom waters. To isolate the anthropogenic CO₂ component (Δ-C_anthro) from Δ-DIC, an extended multilinear regression approach is applied along isopycnal surfaces. This yields an average depth-integrated Δ-C_anthro of 0.53 ± 0.05 mol m^-2 yr^-1 with maximum values in the temperate zones of both hemispheres and a minimum in the tropical Atlantic. A higher decadal increase in the anthropogenic CO₂ inventory is found for the South Atlantic compared to the North Atlantic. This anthropogenic CO₂ accumulation pattern is opposite to that seen for the entire Anthropocene up to the 1990s. This change could perhaps be a consequence of the reduced downward transport of anthropogenic CO₂ in the North Atlantic due to recent climate variability. Extrapolating the results for this section to the entire Atlantic basin (63°N to 56°S) yields an uptake of 5 ± 1 Pg C decade^-1, which corresponds to about 25% of the annual global ocean uptake of anthropogenic CO₂ during this period.

Abstract:

Observations of the surface-water fugacity of carbon dioxide (fCO₂^sw) measured during 2005 in the subpolar North Atlantic Ocean (58-62°N, 10-40°W) were used together with in-situ ocean data and remotely sensed data to develop algorithms to estimate fCO₂^sw. Based on multiple regression, we found that sea-surface temperature (SST), mixed-layer depth (MLD), and chlorophyll a (chl a) contributed significantly to the fit. Two algorithms were developed for periods depending on the presence of chl a data. The correlation coefficient (r²) and the root-mean-square deviation (rms) for the best fit in the period when chl a was observed (20 March-15 October) were 0.720 and ±10.8 µatm, respectively. The best fit for the algorithm for the period when no chl a was present (16 October-19 March) resulted in a r² of 0.774 and a rms of ±5.6 µatm. Based on these algorithms, we estimated seasonal fields of fCO₂^sw and the air-sea CO₂ flux. The estimated net annual CO₂ sink was 0.0058 Gt C yr^-1 or 0.6 mol C m^-2 yr^-1.

Abstract: The National Oceanographic Partnership Program (NOPP) consecutively sponsored the Ocean-Systems for Chemical, Optical, and Physical Experiments (O-SCOPE) and Multi-disciplinary Ocean Sensors for Environmental Analyses and Networks (MOSEAN) projects from 1998 through 2008. The O-SCOPE and MOSEAN projects focused on developing and testing new sensors and systems for autonomous, concurrent measurements of biological, chemical, optical, and physical variables from a diverse suite of stationary and mobile ocean platforms. Design considerations encompassed extended open-ocean and coastal deployments, instrument durability, biofouling mitigation, data accuracy and precision, near-real-time data telemetry, and economythe latter being critical for widespread sensor and system utilization. The complementary O-SCOPE and MOSEAN projects increased ocean sensing and data telemetry capabilities for addressing many societally relevant problems such as global climate change, ocean carbon cycling and sequestration, acidification, eutrophication, anoxia, and ecosystem dynamics, including harmful algal blooms. NOPP support enabled O-SCOPE and MOSEAN to accelerate progress in achieving multiscale, multidisciplinary, sustained observations of the ocean environment. Importantly, both programs produced value-added scientific results, which demonstrated the utility of these new technologies. The NOPP framework fostered strong collaborations among academic, commercial, and government entities, and facilitated technology transfers to the general research community and to long-term observational and observatory programs.

Abstract: We quantify the mechanisms governing interannual variability in the global, upper-ocean inorganic carbon system using a hindcast simulation (1979-2004) of an ecosystem-biogeochemistry model forced with time-evolving atmospheric physics and dust deposition. We analyze the variability of three key, interrelated metrics--air-sea CO₂ flux, surface-water carbon dioxide partial pressure pCO₂, and upper-ocean dissolved inorganic carbon (DIC) inventory--presenting for each metric global spatial maps of the root mean square (rms) of anomalies from a model monthly climatology. The contribution of specific driving factors is diagnosed using Taylor expansions and linear regression analysis. The major regions of variability occur in the Southern Ocean, tropical Indo-Pacific, and Northern Hemisphere temperate and subpolar latitudes. Ocean circulation is the dominant factor driving variability over most of the ocean, modulating surface dissolved inorganic carbon that in turn alters surface-water pCO₂ and air-sea CO₂ flux variability (global integrated anomaly rms of 0.34 Pg C yr^-1). Biological export and thermal solubility effects partially damp circulation-driven pCO₂ variability in the tropics, while in the subtropics, thermal solubility contributes positively to surface-water pCO₂ and air-sea CO₂ flux variability. Gas transfer and net freshwater inputs induce variability in the air-sea CO₂ flux in some specific regions. A component of air-sea CO₂ flux variability (global integrated anomaly rms of 0.14 Pg C yr^-1) arises from variations in biological export production induced by variations in atmospheric iron deposition downwind of dust source regions. Beginning in the mid-1990s, reduced global dust deposition generates increased air-sea CO₂ outgassing in the Southern Ocean, consistent with trends derived from atmospheric CO₂ inversions.

Abstract: Space-based observations provide synoptic coverage of surface ocean temperature, winds, sea surface height, and color useful to a wide range of oceanographic applications. These measurements are increasingly applied to monitor large-scale environmental and climate processes that can have an impact on important managed marine resources. From observing the development of harmful algal blooms using ocean color to tracking regions of thermal stress that can induce coral bleaching, satellites are routinely used for environmental monitoring. Here, we demonstrate an approach to monitoring changes in sea surface ocean chemistry in response to ocean acidification as applied to the greater Caribbean region. The method is based on regionally specific empirical algorithms derived from ongoing ship measurements applied to remotely sensed observables. This tool is important for exploring regional to basinwide trends in ocean acidification on seasonal to interannual time scales.

Abstract:

In order to facilitate the collection of high quality and uniform surface water pCO₂ data, an underway pCO₂ instrument has been designed based on community input and is now commercially available. Along with instrumentation, agreements were reached on data reduction and quality control that can be easily applied to data from these systems by using custom-made freeware. This new automated underway pCO₂ measuring system is designed to be accurate to within 0.1 μatm for atmospheric pCO₂ measurements and to within 2 µatm for seawater pCO₂, targeted by the scientific community to constrain the regional air-sea CO₂ fluxes to 0.2 Pg C year^-1. The procedure to properly reduce the underway pCO₂ data and perform the steps necessary for calculation of the fugacity of CO₂ from the measurements is described. This system is now widely used by the scientific community on many different types of ships. Combined with the recommended data-reduction procedures, it will facilitate producing data sets that will significantly decrease the uncertainty currently present in estimates of air-sea CO₂ fluxes.

Abstract: Here we use observations and ocean models to identify mechanisms driving large seasonal to interannual variations in dissolved inorganic carbon (DIC) and dissolved oxygen (O₂) in the upper ocean. We begin with observations linking variations in upper ocean DIC and O₂ inventories with changes in the physical state of the ocean. Models are subsequently used to address the extent to which the relationships derived from short-timescale (6 months to 2 years) repeat measurements are representative of variations over larger spatial and temporal scales. The main new result is that convergence and divergence (column stretching) attributed to baroclinic Rossby waves can make a first-order contribution to DIC and O₂ variability in the upper ocean. This results in a close correspondence between natural variations in DIC and O₂ column inventory variations and sea surface height (SSH) variations over much of the ocean. Oceanic Rossby wave activity is an intrinsic part of the natural variability in the climate system and is elevated even in the absence of significant interannual variability in climate mode indices. The close correspondence between SSH and both DIC and O₂ column inventories for many regions suggests that SSH changes (inferred from satellite altimetry) may prove useful in reducing uncertainty in separating natural and anthropogenic DIC signals (using measurements from Climate Variability and Predictability's CO₂/Repeat Hydrography program).

Abstract:

No abstract.

Abstract:

A climatological mean distribution for the surface water pCO₂ over the global oceans in non-El Niño conditions has been constructed with spatial resolution of 4° (latitude) x 5° (longitude) for a reference year 2000 based upon about 3 million measurements of surface water pCO₂ obtained from 1970 to 2007. The database used for this study is about 3 times larger than the 0.94 million used for our earlier paper [Takahashi et al., 2002. Global sea-air CO₂ flux based on climatological surface ocean pCO₂, and seasonal biological and temperature effects. Deep-Sea Res. II, 49, 1601-1622]. A time-trend analysis using deseasonalized surface water pCO₂ data in portions of the North Atlantic, North and South Pacific, and Southern Oceans (which cover about 27% of the global ocean areas) indicates that the surface water pCO₂ over these oceanic areas has increased on average at a mean rate of 1.5 µatm y^-1 with basin-specific rates varying between 1.2 ± 0.5 and 2.1 ± 0.4 µatm y^-1. A global ocean database for a single reference year 2000 is assembled using this mean rate for correcting observations made in different years to the reference year. The observations made during El Niño periods in the equatorial Pacific and those made in coastal zones are excluded from the database. Seasonal changes in the surface water pCO₂ and the sea-air pCO₂ difference over four climatic zones in the Atlantic, Pacific, Indian, and Southern Oceans are presented. Over the Southern Ocean seasonal ice zone, the seasonality is complex. Although it cannot be thoroughly documented due to the limited extent of observations, seasonal changes in pCO₂ are approximated by using the data for under-ice waters during austral winter and those for the marginal ice and ice-free zones. The net air-sea CO₂ flux is estimated using the sea-air pCO₂ difference and the air-sea gas transfer rate that is parameterized as a function of (wind speed)² with a scaling factor of 0.26. This is estimated by inverting the bomb ¹⁴C data using Ocean General Circulation models and the 1979-2005 NCEP-DOE AMIP-II Reanalysis (R-2) wind speed data. The equatorial Pacific (14°N-14°S) is the major source for atmospheric CO₂, emitting about +0.48 Pg-C y^-1, and the temperate oceans between 14° and 50° in the both hemispheres are the major sink zones with an uptake flux of -0.70 Pg-C y^-1 for the northern and -1.05 Pg-C y^-1 for the southern zone. The high-latitude North Atlantic, including the Nordic Seas and portion of the Arctic Sea, is the most intense CO₂ sink area on the basis of per unit area, with a mean of -2.5 tons-C month^-1 km^-2. This is due to the combination of the low pCO₂ in seawater and high gas exchange rates. In the ice-free zone of the Southern Ocean (50°-62°S), the mean annual flux is small (-0.06 Pg-C y^-1) because of a cancellation of the summer uptake CO₂ flux with the winter release of CO₂ caused by deepwater upwelling. The annual mean for the contemporary net CO₂ uptake flux over the global oceans is estimated to be -1.6 ± 0.9 Pg-C y^-1, which includes an undersampling correction to the direct estimate of -1.4 ± 0.7 Pg-C y^-1. Taking the pre-industrial steady-state ocean source of 0.4 ± 0.2 Pg-C y^-1 into account, the total ocean uptake flux including the anthropogenic CO₂ is estimated to be -2.0 ± 1.0 Pg-C y^-1 in 2000.

Abstract:

Here we present monthly, basin-wide maps of the partial pressure of carbon dioxide (pCO₂) for the North Atlantic on a 1° latitude by 1° longitude grid for years 2004 through 2006 inclusive. The maps have been computed using a neural network technique which reconstructs the non-linear relationships between three biogeochemical parameters and marine pCO₂. A self organizing map (SOM) neural network has been trained using 389,000 triplets of the SeaWiFS-MODIS chlorophyll-a concentration, the NCEP/NCAR reanalysis sea surface temperature, and the FOAM mixed layer depth. The trained SOM was labelled with 137,000 underway pCO₂ measurements collected in situ during 2004, 2005, and 2006 in the North Atlantic, spanning the range of 208 to 437 µatm. The root mean square error (RMSE) of the neural network fit to the data is 11.6 µatm, which equals to just above 3 per cent of an average pCO₂ value in the in situ dataset. The seasonal pCO₂ cycle as well as estimates of the interannual variability in the major biogeochemical provinces are presented and discussed. High resolution combined with basin-wide coverage makes the maps a useful tool for several applications such as the monitoring of basin-wide air-sea CO₂ fluxes or improvement of seasonal and interannual marine CO₂ cycles in future model predictions. The method itself is a valuable alternative to traditional statistical modelling techniques used in geosciences.

Abstract: The past decade has seen a substantial amount of research on air-sea gas exchange and its environmental controls. These studies have significantly advanced the understanding of processes that control gas transfer, led to higher quality field measurements, and improved estimates of the flux of climate-relevant gases between the ocean and atmosphere. This review discusses the fundamental principles of air-sea gas transfer and recent developments in gas transfer theory, parameterizations, and measurement techniques in the context of the exchange of carbon dioxide. However, much of this discussion is applicable to any sparingly soluble, non-reactive gas. We show how the use of global variables of environmental forcing that have recently become available and gas exchange relationships that incorporate the main forcing factors will lead to improved estimates of global and regional air-sea gas fluxes based on better fundamental physical, chemical, and biological foundations.

Abstract: The oceans are a major sink for atmospheric carbon dioxide (CO₂). Historically, observations have been too sparse to allow accurate tracking of changes in rates of CO₂ uptake over ocean basins, so little is known about how these vary. Here, we show observations indicating substantial variability in the CO₂ uptake by the North Atlantic on time scales of a few years. Further, we use measurements from a coordinated network of instrumented commercial ships to define the annual flux into the North Atlantic, for the year 2005, to a precision of about 10%. This approach offers the prospect of accurately monitoring the changing ocean CO₂ sink for those ocean basins that are well covered by shipping routes.

Abstract:

The global oceans serve as the largest sustained natural sink for increasing atmospheric carbon dioxide (CO₂) concentrations. As this CO₂ is absorbed by seawater, it not only reacts causing a reduction in seawater pH (or acidification) but also decreases the carbonate mineral saturation state (Ω), which plays an important role in calcification for many marine organisms. Ocean acidification could affect some of the most fundamental biological and geochemical processes of the sea in coming decades. Observations obtained in situ from Volunteer Observing Ships and multiple geochemical surveys have been extended using satellite remote sensing and modeled environmental parameters to derive estimates of sea-surface alkalinity (A_T) and carbon dioxide partial pressure (pCO_2,sw). Pairing estimates of A_T and pCO_2,sw have permitted characterization of the changes in sea-surface Ω, which have transpired over the past decade throughout the Greater Caribbean Region as a consequence of ocean acidification. The results reveal considerable spatial and temporal variability throughout the region. Despite this variability, we observed a strong secular decrease in aragonite saturation state (Ω_arg) at a rate of approximately -0.012 ± 0.001 Ω_arg yr^-1 (r² = 0.97, P < 0.001).

Abstract:

The partial pressure of carbon dioxide (pCO₂) in surface seawater on the South Atlantic Bight (SAB) of the United States was measured during six cruises from January 2005 to May 2006. The high-resolution pCO₂ data allow us to create the first maps of the sea surface pCO₂ over the SAB for all seasons. Contrary to an earlier study that was based on limited spatial and seasonal coverage, this study shows that the SAB is a net sink of atmospheric CO₂ on an annual basis (-0.48 ± 0.21 mol m^-2 a^-1). The inner shelf is a source of +1.20 ± 0.24 mol m^-2 a^-1, while the middle and outer shelves are sinks of -1.23 ± 0.19 and -1.37 ± 0.21 mol m^-2 a^-1, respectively. Seasonally, the SAB shifts from a sink for atmospheric CO₂ in winter to a source in summer. The annual cycle of sea surface temperature plays a dominant role in controlling the seasonal variation of the pCO₂. Wind speeds are seasonally anti-correlated with the air-sea pCO₂ differences, and this is an important factor in contributing to the net annual air-sea CO₂ exchange. Factors related to the estimates of CO₂ fluxes in the coastal ocean, such as the choice of wind speeds, the correction of gas transfer equations with nonlinearity coefficients, the effect of diel variations of pCO₂, the spatial extrapolation of the pCO₂ to the nearshore area, and the seasonal interpolation, are also discussed.

Abstract:

Estimates of temporal trends in oceanic anthropogenic carbon dioxide (CO₂) rely on the ability of empirical methods to remove the large natural variability of the ocean carbon system. A coupled carbon-climate model is used to evaluate these empirical methods. Both the ΔC* and multiple linear regression (MLR) techniques reproduce the predicted increase in dissolved inorganic carbon for the majority of the ocean and have similar average percent errors for decadal differences (24.1% and 25.5%, respectively). However, this study identifies several regions where these methods may introduce errors. Of particular note are mode and deep water formation regions, where changes in air-sea disequilibrium and structure in the MLR residuals introduce errors. These results have significant implications for decadal repeat hydrography programs, indicating the need for subannual sampling in certain regions of the oceans in order to better constrain the natural variability in the system and to robustly estimate the intrusion of anthropogenic CO₂.

Abstract:

To improve the spatial and temporal resolution of sea-air carbon dioxide (CO₂) flux estimates in the mid-latitude North Atlantic Ocean (30°N-63°N), empirical relationships were derived between the measured fugacity of CO₂ in surface water (fCO_{2 sw}), sea surface temperature (SST), and the mixed layer depth (MLD). Satellite chlorophyll was unsuccessful as a predictive parameter. The algorithms for fCO_{2 sw} predictions were developed using Advanced Very High Resolution Radiometer (AVHRR) satellite SST and MLD data obtained from Argo floats. The root mean square (RMS) difference between the algorithms and fCO_{2 sw} data was 9-10 µatm with a precision, determined from independent data, of 9-11 µatm. This precision is close to that necessary to constrain the sea-air flux in the mid-latitude North Atlantic Ocean to 0.1 Pg C yr^-1. The algorithms were applied on high-resolution SST and MLD data to yield fCO_{2 sw} proxy data for the entire region. The proxy data served to produce seasonal CO₂ flux maps. In 2002, the mid-latitude North Atlantic was a year-round sink and took up 1.9 mol m^-2 yr^-1.

Abstract: Considerable drawdown of total dissolved inorganic carbon (C_T) and oversaturation of oxygen (O₂) within a cold (15°C) oligotrophic eddy in the extratropical North Atlantic Ocean (46°N, 20.5°W) indicate that, despite the absence of nitrate (NO₃), the eddy was highly productive. Estimates of net community production using the mass balances of C_T and O₂ were two to five times greater than those obtained using the mass balance of NO₃. The remineralization rates obtained using the integrated rates of C_T and NO₃ accumulation and O₂ utilization for the upper thermocline waters (35-300-m depth) were in agreement with C_T- and O₂-based net community production over the same period; however, all the estimates exceeded the NO₃ -based net community production by a factor of two to five, pointing to a considerable accumulation of NO₃ in the upper thermocline in excess of changes in the mixed-layer NO₃ inventory. The amount of this excess NO₃ suggests that a considerable fraction of the net community production was not supported by the mixed-layer NO₃ inventory and that an external source of NO₃ must be present. Of the various mechanisms that might explain the inequity between NO₃ drawdown in the surface layer and NO₃ accumulation in the upper thermocline, N₂ fixation is the most viable yet surprising mechanism for producing such excess NO₃ in this oligotrophic eddy. A significant fraction of net community production in oligotrophic extratropical waters could be supported by processes that are not fully explored or to date have been considered to be insignificant.

Abstract:

No abstract.

Abstract: Observational studies report a rapid decline of ocean CO₂ uptake in the temperate North Atlantic during the last decade. We analyze these findings using ocean physical-biological numerical simulations forced with interannually varying atmospheric conditions for the period 1979-2004. In the simulations, surface ocean water mass properties and CO₂ system variables exhibit substantial multiannual variability on sub-basin scales in response to wind-driven reorganization in ocean circulation and surface warming/cooling. The simulated temporal evolution of the ocean CO₂ system is broadly consistent with reported observational trends and is influenced substantially by the phase of the North Atlantic Oscillation (NAO). Many of the observational estimates cover a period after 1995 of mostly negative or weakly positive NAO conditions, which are characterized in the simulations by reduced North Atlantic Current transport of subtropical waters into the eastern basin and by a decline in CO₂ uptake. We suggest therefore that air-sea CO₂ uptake may rebound in the eastern temperate North Atlantic during future periods of more positive NAO, similar to the patterns found in our model for the sustained positive NAO period in the early 1990s. Thus, our analysis indicates that the recent rapid shifts in CO₂ flux reflect decadal perturbations superimposed on more gradual secular trends. The simulations highlight the need for long-term ocean carbon observations and modeling to fully resolve multiannual variability, which can obscure detection of the long-term changes associated with anthropogenic CO₂ uptake and climate change.

Abstract:

No abstract.

Abstract:

The ratio of carbon-14 (¹⁴C) to carbon in the dissolved inorganic carbon (SIGMA-CO₂) of California's Mono Lake has continued to rise at a rate far faster than expected from the invasion of bomb-test ¹⁴C-labeled atmospheric CO₂. Two explanations can be given. One is that the invasion rate of carbon dioxide from the atmosphere is 5 or so times higher than that for chemically inert gases. The second is that Mono Lake has been used as a site for clandestine disposal of radiocarbon.

Abstract:

No abstract.

Abstract:

Studies deploying atmospheric flux-profile techniques in laboratory wind-wave tanks have been performed to demonstrate and verify the use of air-side turbulent transport models and micrometeorological approaches to accurately determine air-water gas transfer velocities. Air-water gas transfer velocities have been estimated using the CO₂ atmospheric flux-profile technique in laboratory wind-wave tanks both at the NASA Wallops Flight Facility, USA and Kyoto University, Japan. Gas fluxes using the flux-profile and the waterside mass balance techniques have been reconciled. Air-water fluxes of H₂O and momentum were also measured simultaneously in a linear wind-wave tank. The waterside mass balances used the evasion of SF₆. The CO₂, H₂O, and momentum fluxes were calculated using the atmospheric flux-profile technique over a wind speed range of 1 to 14 m s^-1. The CO₂ and H₂O atmospheric profile model uses airside turbulent diffusivities derived from momentum fluxes. These studies demonstrate that the quantification of air-water CO₂ fluxes using the atmospheric flux-profile technique can be implemented in the laboratory. The profile technique can be used to measure an air-water flux in much less time than a mass balance. Effects of surfactants, wind speed, and wind stress on air-water transfer are also explored using the flux-profile technique. Validation of the air-water CO₂ gas exchange in laboratory wind-wave tanks provides evidence and support that this technique may be used in field studies.

Abstract:

No abstract.

Abstract:

The ¹⁴CO₂ released into the stratosphere during bomb testing in the early 1960s provides a global constraint on air-sea gas exchange of soluble atmospheric gases like CO₂. Using the most complete database of dissolved inorganic radiocarbon, DI¹⁴C, available to date and a suite of ocean general circulation models in an inverse mode we recalculate the ocean inventory of bomb-produced DI¹⁴C in the global ocean and confirm that there is a 25% decrease from previous estimates using older DI¹⁴C data sets. Additionally, we find a 33% lower globally averaged gas transfer velocity for CO₂ compared to previous estimates (Wanninkhof, 1992) using the NCEP/NCAR Reanalysis 1 1954-2000 where the global mean winds are 6.9 m s^-1. Unlike some earlier ocean radiocarbon studies, the implied gas transfer velocity finally closes the gap between small-scale deliberate tracer studies and global-scale estimates. Additionally, the total inventory of bomb-produced radiocarbon in the ocean is now in agreement with global budgets based on radiocarbon measurements made in the stratosphere and troposphere. Using the implied relationship between wind speed and gas transfer velocity k_s = 0.27 u₁₀² (Sc/660)^-0.5 and standard partial pressure difference climatology of CO₂ we obtain an net air-sea flux estimate of 1.3 ± 0.5 PgCyr^-1 for 1995. After accounting for the carbon transferred from rivers to the deep ocean, our estimate of oceanic uptake (1.8 ± 0.5 PgCyr^-1) compares well with estimates based on ocean inventories, ocean transport inversions using ocean concentration data, and model simulations.

Abstract:

An autonomous multi-parameter flow-through CO₂ system has been developed to simultaneously measure surface seawater pH, carbon dioxide fugacity (fCO₂), and total dissolved inorganic carbon (DIC). All three measurements are based on spectrophotometric determinations of solution pH at multiple wavelengths using sulfonephthalein indicators. The pH optical cell is machined from a PEEK polymer rod bearing a bore-hole with an optical pathlength of ~15 cm. The fCO₂ optical cell consists of Teflon AF 2400 (DuPont) capillary tubing sealed within the bore-hole of a PEEK rod. This Teflon AF tubing is filled with a standard indicator solution with a fixed total alkalinity, and forms a liquid core waveguide (LCW). The LCW functions as both a long pathlength (~15 cm) optical cell and a membrane that equilibrates the internal standard solution with external seawater. fCO₂ is then determined by measuring the pH of the internal solution. DIC is measured by determining the pH of standard internal solutions in equilibrium with seawater that has been acidified to convert all forms of DIC to CO₂. The system runs repetitive measurement cycles with a sampling frequency of ~7 samples (21 measurements) per hour. The system was used for underway measurements of sea surface pH, fCO₂, and DIC during the CLIVAR/CO₂ A16S cruise in the South Atlantic Ocean in 2005. The field precisions were evaluated to be 0.0008 units for pH, 0.9 µatm for fCO₂, and 2.4 µmol kg^-1 for DIC. These field precisions are close to those obtained in the laboratory. Direct comparison of our measurements and measurements obtained using established standard methods revealed that the system achieved field agreements of 0.0012 ± 0.0042 units for pH, 1.0 ± 2.5 µatm for fCO₂, and 2.2 ± 6.0 µmol kg^-1 for DIC. This system integrates spectrophotometric measurements of multiple CO₂ parameters into a single package suitable for observations of both seawater and freshwater.

Abstract:

Significant advances have been made over the last decade in estimating air-sea CO₂ fluxes over the ocean by the bulk formulation that expresses the flux as the product of the gas transfer velocity and the concentration difference of aqueous CO₂ over the liquid boundary layer. This has resulted in a believable global monthly climatology of air-sea CO₂ fluxes over the ocean on a 4° by 5° grid. It is shown here that the global air-sea CO₂ fluxes are very sensitive to estimates of gas transfer velocity and the parameterization of gas transfer with wind. Wind speeds can now be resolved at sufficient temporal and spatial resolution that they should not limit the estimates, but the absolute magnitudes of winds for different wind products differ significantly. It is recommended to use satellite-derived wind products that have the appropriate resolution instead of assimilated products that often do not appropriately resolve variability on sub-daily and sub-25-km space scales. Parameterizations of gas exchange with wind differ in functional form and magnitude but the difference between the most-used quadratic relationships is about 15%. Based on current estimates of uncertainty of the air-water CO₂ concentration differences, the winds, and the gas exchange-wind speed parameterization, each parameter contributes similarly to the overall uncertainty in the flux that is estimated at 25%.

Abstract:

Air-sea fluxes in the Caribbean Sea are presented based on measurements of partial pressure of CO₂ in surface seawater, pCO_2sw, from an automated system onboard the cruise ship Explorer of the Seas for 2002 through 2004. The pCO_2sw values are used to develop algorithms of pCO_2sw based on sea surface temperature (SST) and position. The algorithms are applied to assimilated SST data and remotely sensed winds on a 1° by 1° grid to estimate the fluxes on weekly timescales in the region. The positive relationship between pCO_2sw and SST is lower than the isochemical trend, suggesting counteracting effects from biological processes. The relationship varies systematically with location with a stronger dependence further south. Furthermore, the southern area shows significantly lower pCO_2sw in the fall compared to the spring at the same SST, which is attributed to differences in salinity. The annual algorithms for the entire region show a slight trend between 2002 and 2004, suggesting an increase of pCO_2sw over time. This is in accord with the increasing pCO_2sw due to the invasion of anthropogenic CO₂. The annual fluxes of CO₂ yield a net invasion of CO₂ to the ocean that ranges from -0.04 to -1.2 mol m^-2 year^-1 over the three years. There is a seasonal reversal in the direction of the flux with CO₂ entering into the ocean during the winter and an evasion during the summer. Year-to-year differences in flux are primarily caused by temperature anomalies in the late winter and spring period resulting in changes in invasion during these seasons. An analysis of pCO_2sw before and after Hurricane Frances (September 4-6, 2004), and wind records during the storm suggest a large local enhancement of the flux but minimal influence on annual fluxes in the region.

Abstract:

No abstract.

Abstract:

In order to determine the interannual and decadal changes in the air-sea carbon fluxes of the equatorial Pacific, we developed seasonal and interannual relationships between the fugacity of CO₂ (fCO₂) and sea surface temperature (SST) from shipboard data that were applied to high-resolution temperature fields deduced from satellite data to obtain high-resolution large-scale estimates of the regional fluxes. The data were gathered on board research ships from November 1981 through June 2004 between 95°W and 165°E. The distribution of fCO_2sw during five El Niño periods and four La Niña periods were documented. Observations made during the warm boreal winter-spring season and during the cooler boreal summer-fall season of each year enabled us to examine the interannual and seasonal variability of the fCO_2sw-SST relationships. A linear fit through all of the data sets yields an inverse correlation between SST and fCO_2sw, with both interannual and seasonal differences in slope. On average, the surface water fCO₂ in the equatorial region has been increasing at a rate similar to the atmospheric CO₂ increase. In addition, there appears to be a slight increase (~27%) in the outgassing flux of CO₂ after the 1997-1998 Pacific Decadal Oscillation (PDO) regime shift. Most of this flux increase is due to increase in wind speeds after the spring of 1998, although increases in fCO_2sw after 1998 are also important. These increases are coincident with the recent rebound of the shallow water meridional overturning circulation in the tropical and subtropical Pacific after the regime shift.

Abstract:

A simple function of sea surface salinity (SSS) and temperature (SST) in the form A_T = a + b (SSS - 35) + c (SSS - 35)² + d (SST - 20) + e (SST - 20)² fits surface total alkalinity (A_T) data for each of five oceanographic regimes within an area-weighted uncertainty of ±8.1 µmol kg^-1 (1 sigma). Globally coherent surface A_T data (n = 5,692) used to derive regional correlations of A_T with SSS and SST were collected during the global carbon survey in the 1990s. Such region-specific A_T algorithms presented herein enable the estimation of the global distribution of surface AT when observations of SSS and SST are available.

Abstract:

Surface seawater pCO₂ and related parameters were measured at high frequency onboard the volunteer observing ship M/V Falstaff in the North Atlantic Ocean between 36° and 52°N. Over 90,000 data points were used to produce monthly CO₂ fluxes for 2002/2003. The air-sea CO₂ fluxes calculated by two different averaging schemes were compared. The first approach used gas transfer velocity determined from wind speed retrieved at the location of the ship and called colocated winds, while for the second approach a monthly averaged gas transfer velocity was calculated from the wind for each grid pixel including the variability in wind. The colocated wind speeds determined during the time of passage do not capture the monthly wind speed variability of the grid resulting in fluxes that were 47% lower than fluxes using the monthly averaged wind products. The Falstaff CO₂ fluxes were in good agreement with a climatology using averaged winds. Over the entire region they differed by 2-5%, depending on the time-dependent correction scheme to account for the atmospheric in increase in pCO₂. However, locally the flux differences between the ship measurements and the climatology were greater, especially in regions north of 45°N, like the eastern sector. A comparison of two wind speed products showed that the annual CO₂ sink is 4% less when using 6 hourly NCEP/NCAR wind speeds compared to the QuikSCAT wind speed data.

Abstract:

The concentration of gaseous carbon dioxide (CO₂) in surface seawater is a fundamental control on the CO₂ flux between the ocean and atmosphere. However, the concentration gradient in the aqueous mass boundary layer determines the magnitude and direction of the flux. The gradients of CO₂ in the aqueous mass boundary layer cannot be measured directly and are usually inferred from partial pressures or fugacities of CO₂ (fCO₂) in the air and water. In addition to the fCO₂, the temperatures at the top and bottom of the aqueous mass boundary layer must be known to determine the thermodynamic driving force of CO₂ gas transfer. Expressing the gradient in terms of the aqueous CO₂ concentration, [CO_2aq], also avoids some conceptual ambiguities. In particular, expressing the CO₂ as a fugacity, which is defined relative to the gas phase, when the gas exchange rate is controlled in the aqueous mass boundary layer often leads to errors in interpretation with respect to changes in boundary layer temperature. As a result, the enhanced CO₂ flux caused by the cool skin effect appears to be overestimated. Apart from the difficulties estimating the temperature at the top and bottom of the aqueous mass boundary layer, the temperature dependence of solubility and fugacity of CO₂ is uncertain to the degree that it can bias air-sea CO₂ flux estimates. The CO_2aq at the surface, [CO_2aq0], is at equilibrium with the atmospheric CO₂ level. As [CO_2aq0] is strongly temperature dependent, it will be significantly higher at high latitude compared to low latitude, while atmospheric CO₂ levels show much less of a gradient.

Abstract:

We infer the year-to-year variability of net global air-sea CO₂ fluxes from observed interannual changes in wind speed and estimated differences in CO₂ partial pressure between surface seawater (pCO_2SW) and the overlying atmosphere. Changes in pCO_2SW are estimated from changes in sea surface temperature via seasonal algorithms that relate pCO_2SW to sea surface temperature. Our diagnostic model yields an interannual variability of ±0.18 petagrams (1-sigma, Pg = 10¹⁵ grams) of carbon per year for the period 1982-2001. El Niño Southern Oscillation-induced changes in the equatorial efflux contribute approximately 70% of the diagnostic modeled global variability. Regional flux anomalies for areas outside the equatorial Pacific are found to neither systematically reinforce nor counteract each other during times of transition from El Niño years to normal years. The interannual variability of ±0.18 Pg C yr^-1 obtained in the present work is at the low end of previous estimates that falls in the range of ±0.2 to ±0.5 Pg C yr^-1. Of the previous estimates, lower values are generally estimated from global ocean circulation-biogeochemical models, while higher values are derived from atmospheric inversion models constrained by atmospheric CO₂ observations. Comparisons of our modeled results with two time series data sets and equatorial Pacific data suggest that our diagnostic model is not able to capture the full range of pCO_2SW variations; this is probably due to the inability of the empirical model to fully account for changes in surface pCO_2SW related to ocean biological and physical processes. The small interannual variability in our modeled fluxes suggests that observed year-to-year variations in the rate of atmospheric CO₂ increase are primarily caused by changes in the rate of CO₂ uptake by the land biosphere.

Abstract:

No abstract.

Abstract:

The ocean plays a major role in the global carbon cycle. Long-term (decadal) changes in ocean carbon inventory are examined by repeating measurements that are made along specific cruise tracks at intervals of 5-15 years. Recent cruises have suggested that the relative role of the Pacific versus the Atlantic storage of CO₂ has changed over the last decade. Shorter-term (daily to inter-annual) changes in ocean carbon uptake are examined with sea-air CO₂ flux estimates from instruments deployed on ships and moorings. The growing surface CO₂ data set also indicates that there is significant interannual variability in the sea-air CO₂ flux.

Abstract:

No abstract.

Abstract:

Surface water pCO₂ data observed over the three decades between 1970 and 2004 are analyzed for space and time (mean decadal) variability in 32 10° x 10° box areas over the North Pacific Ocean north of 10°N. During this period, the pCO₂ values at SST increased at a mean decadal rate of 12.0 ± 4.8 µatm decade^-1 in all but four areas located in the vicinity of the Bering and Okhotsk Seas, where they decreased at a mean rate of -11.1 ± 5.7 µatm decade^-1. The mean rate of increase for the open ocean areas is indistinguishable from the mean atmospheric CO₂ increase rate of 15 µatm decade^-1 (or 1.5 ppm yr^-1) suggesting that the North Pacific surface waters as a whole have been following the atmospheric CO₂ increase. However, the rate of increase varies geographically, reflecting differences in local oceanographic processes including lateral mixing of waters from marginal seas, upwelling of subsurface waters and biological activities. The decrease observed in the southern Bering Sea and the peripheries of the Okhotsk Sea may be accounted for by the combined effects of intensified biological production and changes in lateral and vertical mixing in these areas. The natural logarithm of wintertime pCO₂ values normalized to a constant temperature and salinity of 14.3°C and 34.0 (the basin mean values, respectively) is correlated with winter SST. Using this relationship, the wintertime TCO₂ in mixed layer can be expressed as a function of winter SST with a standard error of ±5 µmol kg^-1.

Abstract:

No abstract.

Abstract:

Patterns of larval dispersal influence the structure of marine biological communities, but many aspects of larval dispersal remain poorly understood. For example, much of our present understanding of larval dispersal is based on models that integrate aspects of physical oceanography and larval biology, but the predictions of those models are generally not tested because we lack the methodology for real-time larval tracking. In the present study, we used both modeled and measured data to track an introduced larval cohort essentially from fertilization to presumed settlement. Larvae of the hard clam Mercenaria were released into a labeled water parcel in the Banana River Lagoon, Florida, within 8.5 hours of nursery production and then were tracked for the duration of their estimated 8-day pelagic life span. Comparisons of modeled versus measured larval distribution indicate that the fate of the larvae as predicted by a tracer model and by the concentration of coincidentally released sulfur hexafluoride (SF₆) did not agree with the fate of the larvae as predicted by the path of subsurface drifters and by a particle trajectory model. Thus, modeled predictions of larval dispersal must be interpreted with care. Additionally, one component of larval dispersal that was observed in the study but that was not accounted for in the model was the spread of larvae along the path of advection. That trail of larvae may have important consequences for patterns of recruitment and resultant community structure, but it is not considered in most treatments of larval dispersal.

Abstract:

No abstract.

Abstract:

The ocean plays a major role in the global carbon cycle as it is a vast reservoir of carbon, naturally exchanges carbon with the atmosphere, and consequently takes up a substantial portion of anthropogenic carbon from the atmosphere. In response to the need for an integrated investigation of the carbon cycle in the oceans, the CLIVAR/CO₂ Repeat Hydrography and NOAA Underway pCO₂ Measurements Programs were established to document the trends in carbon uptake and transport in the global oceans. The CLIVAR/CO₂ Repeat Hydrography Program consists of a systematic re-occupation of select hydrographic sections to quantify global changes in storage and transport of heat, fresh water, carbon dioxide (CO₂), chlorofluorocarbon tracers and related parameters. Three North Atlantic cruises in 2003 marked the beginning of the U.S. effort by reoccupying selected hydrographic sections on decadal time-scales. Early results from these cruises showed significant changes in oxygen and carbon dioxide and several other measurable parameters since the last global survey in the 1990s. The increases of DIC in the Subtropical Mode waters (STMW) are greater than expected from invasion of anthropogenic CO₂ from the atmosphere and may be the result of decadal changes in the local circulation in the North Atlantic.

Abstract:

The U.S. contribution to a large international effort to document long-term trends in carbon storage and transport in the global oceans by reoccupying selected hydrographic sections on decadal timescales began with three North Atlantic cruises in 2003. The initial results from these reoccupation cruises have shown significant long-term changes in oxygen, carbon dioxide (CO₂), and several other measurable parameters since the last global survey, which occurred in 1993. The ocean has a memory of the climate system and is second only to the Sun in affecting variability in the seasons and long-term climate change. The ocean stores an estimated 1000 times more heat than the atmosphere, and 50 times more carbon. Additionally, the key to possible abrupt climate change may lie in deep-ocean circulation.

Abstract:

A novel shipboard gas tension device (GTD) that measures total dissolved air pressure in ocean surface waters is described and demonstrated. In addition, an improved method to estimate dissolved N₂ levels from simultaneous measurements of gas tension, dissolved O₂, water temperature, and salinity is described. Other than a flow-through plenum, the shipboard GTD is similar to the previously described moored-mode GTD (McNeil et al., 1995, Deep-Sea Research, Part I, 42:819-826). The plenum has an integrated water-side screen to protect the membrane and prevent the membrane from flexing in super-saturated near surface waters. The sampling scheme uses a well mixed and thermally insulated 15 L container that is flushed by the ship's seawater intake at a rate of 3-15 L min^-1. Dissolved gas sensors are placed inside this container and flushed with a small recirculation pump. Laboratory data that characterize the response of the modified GTD are presented. The modified GTD has a constant, isothermal, characteristic (e-folding) response time of typically 11±2 min at 20°C. The response time decreases with increasing temperature and varies by ±35% over a temperature range of 5-35°C. Results of field measurements, collected on the R/V Brown between New York and Puerto Rico during September 2002, are presented and provide the first look at co-variability in surface ocean N₂, O₂, and CO₂ levels over horizontal length scales of several kilometers. Dissolved N₂ concentrations decreased by approximately 16% as the ship sailed from the colder northern continental shelf waters, across the Gulf Stream, and into the warmer northwestern Atlantic Ocean. Historical database measurements, buoy time series, and satellite imagery, are used to aid interpretation of the dissolved gas levels.

Abstract:

The lack of a firm relationship between wind speed (U₁₀) and gas transfer velocity (k) is considered to be one of the factors that hinders accurate quantification of interannual variations of ocean-atmosphere CO₂ fluxes. In this paper, the interannual variations of k of using four different k-U₁₀ parameterizations are examined using wind speed data from the NCEP/NCAR reanalysis project. The extent to which interannual variations are faithfully reproduced in the NCEP/NCAR data is also investigated. This is carried out through comparison with QuikSCAT data. Compared with 4 years of QuikSCAT data, NCEP/NCAR data reproduce interannual k variations, although the absolute magnitude of k is underestimated. Interannual k variation shows great sensitivity to selection of k-U₁₀ parameterization, and in the Westerlies it changes by a factor of three depending on k-U₁₀ parameterization. Use of monthly mean winds speeds leads to overestimation of interannual k variations compared with k variations computed using 6-hourly wind speeds and the appropriate k-U₁₀ parameterization. Even though the effect of changing k-U₁₀ parameterization is large enough to be an issue that needs to be considered when computing interannual air-sea CO₂ flux variations through combining estimates of k with data for the air-sea CO₂ gradient, it is not sufficient to bridge the gap between such estimates and estimates based on analyses of atmospheric oxygen, CO₂, and delta¹³C data. Finally, it is shown that the ambiguity in the relationship between wind speed and k introduces an uncertainty in interannual flux variations comparable to a bias of interannual DELTApCO₂ variations of at most ?5 µatm.

Abstract:

This report presents methods and analytical and quality control procedures for nutrient, oxygen, and inorganic carbon system parameters performed during the A16N_2003a cruise, which took place from June 4 to August 11, 2003 aboard NOAA Ship R/V Ronald H. Brown under auspices of the National Oceanic and Atmospheric Administration (NOAA). The first hydrographic leg (June 19-July 10) was from Reykjavik, Iceland, to Funchal, Madeira, Portugal along the 20°W meridian, and the second leg (July 15-August 11) continued operations from Funchal, Portugal to Natal, Brazil, on a track southward and ending at 6°S, 25°W. The research was the first in a decadal series of repeat hydrography sections jointly funded by NOAA and the National Science Foundation (NSF) as part of the CLIVAR/CO₂/hydrography/tracer program. Samples were taken from up to 34 depths at 150 stations. The data presented in this report includes the analyses of water samples for total inorganic carbon (TCO₂), fugacity of CO₂ (fCO₂), total alkalinity (TALK), pH, nitrate (NO₃), nitrite (NO₂), phosphate (PO₄), silicate (SiO₄), and dissolved oxygen (O₂). The R/V Ronald H. Brown A16N_2003a data set is available free of charge as a numeric data package (NDP) from the Carbon Dioxide Information Analysis Center (CDIAC). The NDP consists of the oceanographic data files and this printed documentation, which describes the procedures and methods used to obtain the data.

Abstract:

During the 1990s, ocean sampling expeditions were carried out as part of the World Ocean Circulation Experiment, the Joint Global Ocean Flux Study, and the Ocean Atmosphere Carbon Exchange Study. Most of the cruises included various inorganic carbon species among the suite of routinely measured parameters. Both during and after the field work, a group of U.S. scientists collaborated to synthesize the data into easily usable and readily available products. This collaboration is known as the Global Ocean Data Analysis Project (GLODAP). Both measured results and calculated quantities were merged into common-format data sets, segregated by ocean. The carbon data were subjected to rigorous secondary quality control procedures, beyond those typically performed on individual cruise data, to eliminate systematic biases in the basin-scale compilations. For comparison purposes, each ocean data set included results from a small number of high-quality historical cruises. The calibrated 1990s data were used to estimate anthropogenic CO₂, potential alkalinity, chlorofluorocarbon (CFC) water mass ages, CFC partial pressure, bomb-produced radiocarbon, and natural radiocarbon. The calibrated-merged data were used to produce objectively gridded global property maps designed to match existing climatologies for temperature, salinity, oxygen, and nutrients. Both the data sets and the gridded products are available from the Carbon Dioxide Information Analysis Center (CDIAC). Here we summarize important details of the data assembly, calibration, calculations, and mapping. The synthesis was carried out one ocean at a time, progressing from the Indian to the Pacific and ending with the Atlantic. The entire synthesis required about five years. During that period, new methods were developed and old ones modified. At the same time, the data set itself changed and expanded. Many of the GLODAP results are already published. Rather than repeat what is published, we concentrate here on summarizing important details of the data assembly and mapping. In particular, we focus on the procedural differences that evolved as the individual basin data sets were compiled and developments in the data set that have not been covered in the individual publications. Some of the GLODAP publications are attached as appendices. The GLODAP data set described here (Gv1.1) is available free of charge as a numeric data package (NDP-83) from CDIAC. The data, and any subsequent updates, are also available through the GLODAP web site (http://cdiac.ornl.gov/oceans/glodap/Glodap_home.htm). The GLODAP bottle data files are available in flat ASCII file data format, in Ocean Data View (ODV) format, and through the CDIAC live access server (LAS); the gridded data files are available in flat ASCII and NetCDF data file formats and through CDIAC LAS.

Abstract:

No abstract.

Abstract:

Pathways and dilution of a point source ocean discharge in the farfield (approximately equal to 10-66 km) were measured using the deliberate tracer sulfur hexafluoride (SF₆). The injection of SF₆ was performed by bubbling the gas over a period of 6 days into an ocean outfall pipe discharging into the southeast Florida coastal ocean. The surface SF₆ concentrations show that the discharged water flowed northward parallel to the coast with a broadening of the width of the plume to about 3 km at the farthest point sampled, 66 km from the outfall. The discharge was fully mixed throughout the water column within 13 km of the outfall terminus. In the first 20 km from the outfall, SF₆ surface concentrations were highly variable, while beyond this the SF₆ concentrations decreased monotonically going northward. The currents were measured during the study with a bottom-mounted acoustic Doppler current profiler (ADCP) located 5.5 km from the outfall. Velocities were variable in magnitude and direction but showed a net northward flow during the 6-day study. Maximum concentrations decreased by about 200-fold per kilometer from the outfall to the northern end of the study area. The study shows that SF₆ is an effective method to trace point source releases far from their origin.

Abstract:

This report presents methods, and analytical and quality control procedures for salinity, oxygen, nutrient, inorganic carbon, organic carbon, chlorofluorocarbon (CFC), and bomb ¹⁴C system parameters performed during the A16S_2005 cruise, which took place from January 11 to February 24, 2005, aboard research vessel (R/V) Ronald H. Brown under the auspices of the National Oceanic and Atmospheric Administration (NOAA). The R/V Ronald H. Brown departed Punta Arenas, Chile, on January 11, 2005, and ended its cruise in Fortaleza, Brazil, on February 24, 2005. The research conducted was one of a series of repeat hydrography sections jointly funded by NOAA and the National Science Foundation as part of the CLIVAR/CO₂/Repeat Hydrography/Tracer Program. Samples were taken from 36 depths at 121 stations. The data presented in this report include the analyses of water samples for total inorganic carbon (TCO₂), fugacity of CO₂ (fCO₂), total alkalinity (TALK), pH, dissolved organic carbon (DOC), CFC, ¹⁴C, hydrographic, and other chemical measurements. The R/V Ronald H. Brown A16S_2005 data set is available free of charge as a numeric data package (NDP) from the Carbon Dioxide Information Analysis Center (CDIAC). The NDP consists of the oceanographic data files and this printed documentation, which describes the procedures and methods used to obtain the data.

Abstract:

The availability of iron is known to exert a controlling influence on biological productivity in surface waters over large areas of the ocean and may have been an important factor in the variation of the concentration of atmospheric carbon dioxide over glacial cycles. The effect of iron in the Southern Ocean is particularly important because of its large area and abundant nitrate, yet iron-enhanced growth of phytoplankton may be differentially expressed between waters with high silicic acid in the south and low silicic acid in the north, where diatom growth may be limited by both silicic acid and iron. Two mesoscale experiments, designed to investigate the effects of iron enrichment in regions with high and low concentrations of silicic acid, were performed in the Southern Ocean. These experiments demonstrate iron's pivotal role in controlling carbon uptake and regulating atmospheric partial pressure of carbon dioxide.

Abstract:

We characterized pCO₂ variability on hourly to weekly time scales during the 14-day GasEx-2001 Lagrangian drifter experiment in the eastern equatorial Pacific Ocean. Underway pCO₂ was recorded at 5 m depth as the ship closely followed a drogued drifter. Dissolved O₂ (DO) was measured at 10 and 15 m depths using in situ sensors deployed on the drogue. Diel pCO₂ and DO variability is evaluated using a simple model that accounts for air-sea exchange, vertical mixing, heating, and net community metabolism. Mixed-layer depths and local (vertical) entrainment are estimated with the Price Weller Pinkel (PWP) mixed-layer model. The mean observed pCO₂ was 472.0 ± 1.8 µatm with a diel increase of 2-6 µatm on most days, near coincident in time with the diel peak in temperature. The biogeochemical model reveals that heating was the primary source of diel pCO₂ variability, but net community production and depletion of CO₂ in the shallow warm layer due to air-sea gas exchange reduced the heating-driven peak by ~1-4 and 1-2 µatm each day, respectively. The same model parameterizations also accurately predict the diel DO amplitude. In the model, atmospheric exchange depletes total CO₂ and DO in the surface layer, and the depleted water is mixed with the isolated underlying water during nocturnal convection. The 10- and 15-m DO time series corroborate these predicted dynamics. Over the 14-day study, net heating offset the expected ~14 µatm decrease due to air-sea CO₂ exchange and net community production, resulting in a nearly constant mean pCO₂. Consequently, net heating acts to sustain high air-sea CO₂ fluxes in the upwelled equatorial Pacific water as the water advects westward in the South Equatorial Current.

Abstract:

No abstract.

Abstract:

No abstract.

Abstract:

During the recent GasEx-2001 cruise in the equatorial Pacific aboard the NOAA ship Ronald H. Brown, carbon measurements were made in the region of 3°S, 125°W. Continuous surface water fCO₂ measurements were conducted onboard in both underway and discrete analysis modes. During the 15-day experiment, surface water fCO₂ values averaged 473 ± 2 µatm, providing a constant condition of supersaturation and flux of CO₂ from the ocean to the atmosphere. The relationship of gas transfer with wind speed developed in this study is used along with regional estimates of air-water fCO₂ differences to determine CO₂ fluxes in the equatorial Pacific. The regional fCO₂ fields are estimated from algorithms developed from previous measurements collected on the Ronald H. Brown and Ka'imimoana over the past 10 years between 5°N and 10°S, 90°W and 165°E. Using the W. McGillis et al. gas transfer-wind speed relationship, we estimate an average flux of 1.5 ± 0.4 mol C m^-2 yr^-1 for the study region, with a six-fold difference in the regional efflux of CO₂ between the strong El Niño events of 1986-1987 and 1997-1998 and the La Niña events of 1996 and 1999-2001 (i.e., 0.1 to 0.56 Pg C yr^-1). The combined effects of uncertainties in the gas transfer velocity and wind fields lead to average difference of 27% between the lowest and highest estimates of the CO² flux from the region. In contrast, the uncertainties in the fCO₂-SST relationships give an average difference of about 35% between the lowest and highest estimates of the CO₂ flux.

Abstract:

During the two recent GasEx field experiments, direct covariance measurements of air-sea carbon dioxide fluxes were obtained over the open ocean. Concurrently, the National Oceanic and Atmospheric Administration/Coupled-Ocean Atmospheric Response Experiment air-sea gas transfer parameterization was developed to predict gas transfer velocities from measurements of the bulk state of the sea surface and atmosphere. The model output is combined with measurements of the mean air and sea surface carbon dioxide fugacities to provide estimates of the air-sea CO₂ flux, and the model is then tuned to the GasEx-1998 data set. Because of differences in the local environment and, possibly, because of weaknesses in the model, some discrepancies are observed between the predicted fluxes from the GasEx-1998 and GasEx-2001 cases. To provide an estimate of the contribution to the air-sea flux of gas due to wave-breaking processes, the whitecap and bubble parameterizations are removed from the model output. These results show that moderate (approximately 15 m s^-1) wind speed breaking wave gas transfer processes account for a fourfold increase in the flux over the modeled interfacial processes.

Abstract:

During the 1990s, ocean sampling expeditions were carried out as part of the World Ocean Circulation Experiment (WOCE), the Joint Global Ocean Flux Study (JGOFS), and the Ocean Atmosphere Carbon Exchange Study (OACES). Subsequently, a group of U.S. scientists synthesized the data into easily usable and readily available products. This collaboration is known as the Global Ocean Data Analysis Project (GLODAP). Results were merged into a common format data set, segregated by ocean. For comparison purposes, each ocean data set includes a small number of high-quality historical cruises. The data were subjected to rigorous quality control procedures to eliminate systematic data measurement biases. The calibrated 1990s data were used to estimate anthropogenic CO₂, potential alkalinity, CFC watermass ages, CFC partial pressure, bomb-produced radiocarbon, and natural radiocarbon. These quantities were merged into the measured data files. The data were used to produce objectively gridded property maps at a 1° resolution on 33 depth surfaces chosen to match existing climatologies for temperature, salinity, oxygen, and nutrients. The mapped fields are interpreted as an annual mean distribution in spite of the inaccuracy in that assumption. Both the calibrated data and the gridded products are available from the Carbon Dioxide Information Analysis Center. Here we describe the important details of the data treatment and the mapping procedure, and present summary quantities and integrals for the various parameters.

Abstract:

GasEx-2001, a 15-day air-sea carbon dioxide (CO₂) exchange study conducted in the equatorial Pacific, used a combination of ships, buoys, and drifters equipped with ocean and atmospheric sensors to assess variability and surface mechanisms controlling air-sea CO₂ fluxes. Direct covariance and profile method air-sea CO₂ fluxes were measured together with the surface ocean and marine boundary layer processes. The study took place in February 2001 near 125°W, 3°S in a region of high CO₂. The diurnal variation in the air-sea CO₂ difference was 2.5%, driven predominantly by temperature effects on surface solubility. The wind speed was 6.0 ± 1.3 m s^-1, and the atmospheric boundary layer was unstable with conditions over the range -1 < z/L < 0. Diurnal heat fluxes generated daytime surface ocean stratification and subsequent large nighttime buoyancy fluxes. The average CO₂ flux from the ocean to the atmosphere was determined to be 3.9 mol m^-2 yr^-1, with nighttime CO₂ fluxes increasing by 40% over daytime values because of a strong nighttime increase in (vertical) convective velocities. The 15 days of air-sea flux measurements taken during GasEx-2001 demonstrate some of the systematic environmental trends of the eastern equatorial Pacific Ocean. The fact that other physical processes, in addition to wind, were observed to control the rate of CO₂ transfer from the ocean to the atmosphere indicates that these processes need to be taken into account in local and global biogeochemical models. These local processes can vary on regional and global scales. The GasEx-2001 results show a weak wind dependence but a strong variability in processes governed by the diurnal heating cycle. This implies that any changes in the incident radiation, including atmospheric cloud dynamics, phytoplankton biomass, and surface ocean stratification may have significant feedbacks on the amount and variability of air-sea gas exchange. This is in sharp contrast with previous field studies of air-sea gas exchange, which showed that wind was the dominating forcing function. The results suggest that gas transfer parameterizations that rely solely on wind will be insufficient for regions with low to intermediate winds and strong insolation.

Abstract:

No abstract.

Abstract:

Empirical relationships between sea surface carbon dioxide fugacity (fCO₂^sw) and sea surface temperature (SST) were applied to data sets of remotely sensed SST to create fCO₂^sw fields in the Caribbean Sea. SST data sets from different sensors were used, as well as the SST fields created by optimum interpolation of bias corrected AVHRR data. Empirical relationships were derived using shipboard fCO₂^sw data, in situ SST data, and SST data from the remote sensing platforms. The results show that the application of a relationship based on shipboard SST data, on fields of remotely sensed SST yields biased fCO₂^sw values. This bias is reduced if the fCO₂^sw-SST relationships are derived using the same SST data that are used to create the SST fields. The fCO₂^sw fields found to best reproduce observed fCO₂^sw are used in combination with wind speed data from QuikSCAT to create weekly maps of the sea-air CO₂ flux in the Caribbean Sea in 2002. The region to the southwest of Cuba was a source of CO₂ to the atmosphere throughout 2002, and the region to the northeast was a sink during winter and spring and a source during summer and fall. The net uptake of CO₂ in the region was doubled when potential skin layer effects on fCO₂^sw were taken into account.

Abstract:

Using inorganic carbon measurements from an international survey effort in the 1990s and a tracer-based separation technique, we estimate a global oceanic anthropogenic carbon dioxide (CO₂) sink for the period from 1800 to 1994 of 118 ± 19 petagrams of carbon. The oceanic sink accounts for ∼48% of the total fossil-fuel and cement-manufacturing emissions, implying that the terrestrial biosphere was a net source of CO₂ to the atmosphere of about 39 ± 28 petagrams of carbon for this period. The current fraction of total anthropogenic CO₂ emissions stored in the ocean appears to be about one-third of the long-term potential.

Abstract:

No abstract.

Abstract:

No abstract.

Abstract:

Gas transfer velocities were determined in the Southern Ocean during the Southern Ocean Iron Fertilization experiment (SOFex) using the dual deliberate tracer technique. The decrease of the purposefully injected tracers, sulfur hexafluoride and helium-3, could be well described by gas exchange parameterizations with wind speed that satisfy global constraints based on bomb-¹⁴C uptake. The concentration decrease of tracers could be predicted slightly better with established relationships if gas transfer was modeled as a function of the cube rather than the square of the wind speed, particularly over a time interval with high and variable winds. However, both fits can model the concentration decrease within the uncertainty of the observations. This suggests that it will be singularly difficult to definitively determine if a quadratic or cubic dependence of gas exchange with wind is more appropriate based on deliberate tracer measurements. However, these results show that gas exchange rates in the Southern Ocean are not anomalous when compared with the rest of the ocean. Thus, this cannot account for discrepancy between observational and model-based estimates of uptake of CO₂ in the Southern Ocean. Using a high-quality wind speed field obtained from the QuikSCAT satellite Seawinds scatterometer and an established surface water pCO₂ climatology, the CO₂ uptake in the Southern Ocean (>34°S) is reassessed. The total uptake rates are similar to previous observation-based estimates, but the analysis shows that the uptake rate is sensitive to wind speed product used and the wind speed distribution.

Abstract:

The Skin Depth Experimental Profiler (SkinDeEP) is an autonomous, self-contained, hydrodynamic instrument capable of making repeated, high-resolution profiles of temperature and conductivity within the ocean's upper decameter. Autonomous profiling operation is accomplished through SkinDeEP's ability to change its density: positive buoyancy is achieved by pumping air from inside the body of the profiler into an external, neoprene, inflatable sleeve; the instrument sinks when the sleeve is deflated by returning the air to the interior. The sensors are mounted some distance from the top endcap and data are recorded only during the ascending phase of the profile so as to minimize disruption of a naturally occurring scalar structure by the presence of the instrument. Temperature and conductivity are measured with resolutions in the submillimeter and millimeter ranges, respectively. Highly accurate and slower sensors are installed for calibration purposes. These data are used to study exchange processes at the air-sea interface and the structure of the ocean just below.

Abstract:

The difference in the fugacities of CO₂ across the diffusive sublayer at the ocean surface is the driving force behind the air-sea flux of CO₂. Bulk seawater fugacity is normally measured several meters below the surface, while the fugacity at the water surface, assumed to be in equilibrium with the atmosphere, is measured several meters above the surface. Implied in these measurements is that the fugacity values are the same as those across the diffusive boundary layer. However, temperature gradients exist at the interface due to molecular transfer processes, resulting in a cool surface temperature, known as the skin effect. A warm layer from solar radiation can also result in a heterogeneous temperature profile within the upper few meters of the ocean. Here we describe measurements carried out during a 14-day study in the equatorial Pacific Ocean (GasEx-2001) aimed at estimating the gradients of CO₂ near the surface and resulting flux anomalies. The fugacity measurements were corrected for temperature effects using data from the ship's thermosalinograph, a high-resolution profiler (SkinDeEP), an infrared radiometer (CIRIMS), and several point measurements at different depths on various platforms. Results from SkinDeEP show that the largest cool skin and warm layer biases occur at low winds, with maximum biases of -4% and +4%, respectively. Time series ship data show an average CO₂ flux cool skin retardation of about 2%. Ship and drifter data show significant CO₂ flux enhancement due to the warm layer, with maximums occurring in the afternoon. Temperature measurements were compared to predictions based on available cool skin parameterizations to predict the skin-bulk temperature difference, along with a warm layer model.

Abstract:

Recent independent lines of evidence suggest that the dissolution of calcium carbonate (CaCO₃) particles is substantial in the upper ocean above the calcite 100% saturation horizon. This shallow-water dissolution of carbonate particles is in contrast with the current paradigm of the conservative nature of pelagic CaCO₃ at shallow water depths. Here we use more than 20,000 sets of carbon measurements in conjunction with CFC and ¹⁴C data from the WOCE/JGOFS/OACES global CO₂ survey to estimate in-situ dissolution rates of CaCO₃ in the Atlantic Ocean. A dissolution rate is estimated from changes in alkalinity as a parcel of water ages along an isopycnal surface. The in-situ CaCO₃ dissolution increases rapidly at the aragonite 100% saturation horizon. Estimated dissolution rates north of 40°N are generally higher than the rates to the south, which is partly attributable to the production of exported CaCO₃ being higher in the North Atlantic than in the South Atlantic. As more CaCO₃ particles move down the water column, more particles are available for in-situ dissolution. The total water column CaCO₃ dissolution rate in the Atlantic Ocean is determined on an annual basis by integrating estimated dissolution rates throughout the entire water column and correcting for alkalinity input of approximately 5.6 x 10¹² mol C yr^-1 from CaCO₃-rich sediments. The resulting water column dissolution rate of CaCO₃ for the Atlantic Ocean is approximately 11.1 x 10¹² mol C yr^-1. This corresponds to about 31% of a recent estimate (35.8 x 10¹² mol C yr^-1) of net CaCO₃ production by Lee (2001) for the same area. Our calculation using a large amount of high-quality water column alkalinity data provides the first basin-scale estimate of the CaCO₃ budget for the Atlantic Ocean.

Abstract:

The relationship between gas transfer velocity and wind speed was evaluated at low wind speeds by quantifying the rate of evasion of the deliberate tracer, SF₆, from a small oligotrophic lake. Several possible relationships between gas transfer velocity and low wind speed were evaluated by using 1-min-averaged wind speeds as a measure of the instantaneous wind speed values. Gas transfer velocities in this data set can be estimated virtually equally well by assuming any of three widely used relationships between k₆₀₀ and winds referenced to 10-m height, U₁₀: (1) a bilinear dependence with a break in the slope at ~3.7 m s^-1, which resulted in the best fit; (2) a power dependence; and (3) a constant transfer velocity for U₁₀ < ~3.7 m s^-1, with a linear dependence on wind speed at higher wind speeds. The lack of a unique relationship between transfer velocity and wind speed at low wind speeds suggests that other processes, such as convective cooling, contribute significantly to gas exchange when the wind speeds are low. All three proposed relationships clearly show a strong dependence on wind for winds >3.7 m s^-1 which, coupled with the typical variability in instantaneous wind speeds observed in the field, leads to average transfer velocity estimates that are higher than those predicted for steady wind trends. The transfer velocities predicted by the bilinear steady wind relationship for U₁₀ < ~3.7 m s^-1 are virtually identical to the theoretical predictions for transfer across a smooth surface.

Abstract:

This paper presents a comprehensive analysis of the basin-wide inventory of anthropogenic CO₂ in the Atlantic Ocean based on high-quality inorganic carbon, alkalinity, chlorofluorocarbon, and nutrient data collected during the World Ocean Circulation Experiment (WOCE) Hydrographic Program, the Joint Global Ocean Flux Study (JGOFS), and the Ocean-Atmosphere Carbon Exchange Study (OACES) surveys of the Atlantic Ocean between 1990 and 1998. Anthropogenic CO₂ was separated from the large pool of dissolved inorganic carbon using an extended version of the DELTA-C* method originally developed by Gruber et al. (1996). The extension of the method includes the use of an optimum multiparameter analysis to determine the relative contributions from various source water types to the sample on an isopycnal surface. Total inventories of anthropogenic CO₂ in the Atlantic Ocean are highest in the subtropical regions at 20°-40°, whereas anthropogenic CO₂ penetrates the deepest in high-latitude regions (>40°N). The deeper penetration at high northern latitudes is largely due to the formation of deep water that feeds the Deep Western Boundary Current, which transports anthropogenic CO₂ into the interior. In contrast, waters south of 50°S in the Southern Ocean contain little anthropogenic CO₂. Analysis of the data collected during the 1990-1998 period yielded a total anthropogenic CO₂ inventory of 28.4 ± 4.7 Pg C in the North Atlantic (equator-70°N) and of 18.5 ± 3.9 Pg C in the South Atlantic (equator-70°S). These estimated basin-wide inventories of anthropogenic CO₂ are in good agreement with previous estimates obtained by Gruber (1998), after accounting for the difference in observational periods. Our calculation of the anthropogenic CO₂ inventory in the Atlantic Ocean, in conjunction with the inventories calculated previously for the Indian Ocean (Sabine et al., 1999) and for the Pacific Ocean (Sabine et al., 2002), yields a global anthropogenic CO₂ inventory of 112 ± 17 Pg C that has accumulated in the world oceans during the industrial era. This global oceanic uptake accounts for approximately 29% of the total CO₂ emissions from the burning of fossil fuels, land-use changes, and cement production during the past 250 years.

Abstract:

In January and February 1998, when an unprecedented fourth repetition of the zonal hydrographic transect at 24.5°N in the Atlantic was undertaken, carbon measurements were obtained for the second time in less than a decade. The field of total carbon along this section is compared to that provided by a 1992 cruise which followed a similar path (albeit in a different season). Consistent with the increase in atmospheric carbon levels, an increase in anthropogenic carbon concentrations of 8 ± 3 mol kg^-1 was found in the surface layers. Using an inverse analysis to determine estimates of absolute velocity, the flux of inorganic carbon across 24.5° is estimated to be -0.74 ± 0.91 and -1.31 ± 0.99 Pg Cyr^-1 southward in 1998 and 1992, respectively. Estimates of total inorganic carbon flux depend strongly upon the estimated mass transport, particularly of the Deep Western Boundary Current. The 1998 estimate reduces the large regional divergence in the meridional carbon transport suggested by previous studies and brings into question the idea that the tropical Atlantic constantly outgasses carbon, while the subpolar Atlantic sequesters it. Uncertainty in the carbon transports themselves, dominated by the uncertainty in the total mass transport estimates, are a hindrance to determining the "true" picture. The flux of anthropogenic carbon (C*_ANTH) across the two transects is estimated as northward at 0.20 ± 0.08 and 0.17 ± 0.06 Pg Cyr^-1 for the 1998 and 1992 sections, respectively. The net transport of C*_ANTH across 24.5°N is strongly affected by the difference in concentrations between the northward flowing shallow Florida Current and the mass balancing, interior return flow. The net northward transport of C*_ANTH is opposite the net flow of total carbon and suggests, as has been found by others, that the pre-industrial southward transport of carbon within the Atlantic was stronger than it is today. Combining these flux results with estimates of atmospheric and riverine inorganic carbon input, it is determined that today's oceanic carbon system differs from the pre-industrial system in that today there is an uptake of anthropogenic carbon to the south that is advected northward and stored within the North Atlantic basin.

Abstract:

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Abstract:

The multiple-parameter linear regression method (Monitoring global ocean carbon inventories, Ocean Observing System Development Panel, Texas A&M University, College Station, TX, 1995, 54 pp; Global Biogeochem. Cycles, 13 (1999) 179) is used to compare inorganic carbon data from the GEOSECS CO₂ survey in the Pacific Ocean in 1973 to the WOCE/JGOFS global CO₂ survey in the 1990s. A model of total dissolved inorganic carbon (DIC) as a function of five variables (AOU, theta, S, Si, and PO₄) has been developed from the recent CO₂ survey data (namely CGC91 and CGC96) in the Pacific Ocean. After correcting for a systematic DIC offset of -30.3 ± 7 mol kg^-1 from the GEOSECS data, the residual DIC based on this model as computed from GEOSECS data has been used to estimate the anthropogenic CO₂ penetration in the Pacific Ocean. In the Northeast Pacific, we obtained an increase of CO₂ of 21.3 ± 7.9 mol m^-2 over the period from GEOSECS in 1973 to CGC91 in 1991. This gives a mean anthropogenic CO₂ uptake rate of 1.3 ± 0.5 mol m^-2 yr^-1 over this 17 year time period. In the South Pacific, north of 50°S between 180° and 120°W region, the integrated anthropogenic CO₂ inventory is estimated to be 19.7 ± 5.7 mol m^-2 over the period from GEOSECS in 1974 to CGC96 in 1996. The equivalent mean CO₂ uptake rate is estimated to be 0.9 ± 0.3 mol m^-2 yr^-1 over the 22 years. These results are compared with the isopycnal method (Nature, 396 (1998) 560) to estimate the anthropogenic CO₂ signal in the Northeast Pacific (30°N, 152°W) at the crossover region between CGC91 and GEOSECS. The results of the isopycnal method are consistent with those derived from the MLR method. Both methods show an increase in anthropogenic CO₂ inventory in the ocean over two decades that is consistent with the increase expected if the ocean uptake has kept pace with the atmospheric CO₂ increase.

Abstract:

No abstract.

Abstract:

As part of the global synthesis effort sponsored by the Global Carbon Cycle project of the National Oceanic and Atmospheric Administration (NOAA) and U.S. Department of Energy, a comprehensive comparison was performed of inorganic carbon parameters measured on oceanographic surveys carried out under the auspices of the Joint Global Ocean Flux Study and related programs. Many of the cruises were performed as part of the World Hydrographic Program of the World Ocean Circulation Experiment and the NOAA Ocean-Atmosphere Carbon Exchange Study. Total dissolved inorganic carbon (DIC), total alkalinity (TAlk), fugacity of CO₂, and pH data from 23 cruises were checked to determine whether there were systematic offsets of these parameters between cruises. The focus was on the DIC and TAlk state variables. Data quality and offsets of DIC and TAlk were determined by using several different techniques. One approach was based on crossover analyses, where the deep-water concentrations of DIC and TAlk were compared for stations on different cruises that were within 100 km of each other. Regional comparisons were also made by using a multiple-parameter linear regression technique in which DIC or TAlk was regressed against hydrographic and nutrient parameters. When offsets of greater than 4 µmol/kg were observed for DIC and/or 6 µmol/kg were observed for TAlk, the data taken on the cruise were closely scrutinized to determine whether the offsets were systematic. Based on these analyses, the DIC data and TAlk data of three cruises were deemed of insufficient quality to be included in the comprehensive basinwide data set. For several of the cruises, small adjustments in TAlk were recommended for consistency with other cruises in the region. After these adjustments were incorporated, the inorganic carbon data from all cruises, along with hydrographic, chlorofluorocarbon, and nutrient data, were combined as a research-quality product for the scientific community.

Abstract:

GasEx-98 was an air-sea exchange process cruise conducted aboard the NOAA ship Ronald H. Brown in the North Atlantic during May and June of 1998. During the cruise, air-sea gas transfer velocities for carbon dioxide were measured using the direct-covariance method. Because the sampling times for the covariance method are on the same order as the time scales of changes in meteorological forcing, the GasEx-98 results provide a unique data set for investigating whether changes in different forcing mechanisms correlate with changes in gas transfer. In particular, fractional area whitecap coverage, W_C, was measured during daylight hours using a dual-camera video system mounted on a bow tower. Several high wind speed events occurred during the cruise, and the resulting correlation between wind speed and W_C is consistent with previous oceanic measurements. The whitecap coverage data were combined with the wind speed records and these data were used in a parameterization of whitecap-mediated gas transfer to predict transfer velocities. These predicted transfer velocities are in good agreement with the transfer velocities derived from the direct-covariance data.

Abstract:

This report recommends a strategy for making observations of carbon dioxide (CO₂) and related properties in the atmosphere and oceans, over large spatial scales and long timescales. It also recommends process studies of air-sea gas exchange, in order to obtain more accurate estimates of CO₂ transfer between the atmosphere and oceans. Models are essential tools for understanding the distributions and fluxes of CO₂ in the atmosphere and oceans. We recommend observations and modeling efforts to enhance the skills of models used for this purpose. An ultimate product of the observations, modeling efforts, and complementary process studies will be improved projections of the trajectory of the atmospheric CO₂ increase. The report's recommendations are summarized in Table E-1. These recommendations are prepared in the context of the U.S. Carbon Cycle Science Plan (CCSP), with the goal of advancing our ability to address the two fundamental questions that the CCSP posed: (1) what has happened to the carbon dioxide that has already been emitted by human activities (past anthropogenic CO₂); and (2) what will be the future atmospheric CO₂ concentration trajectory resulting from both past and future emissions? The importance of answering these questions is evident. A recent National Research Council report, Climate Change Science, documents the consensus scientists have reached that human emissions of greenhouse gases are increasingly affecting world climate. The President's speech to the nation on global climate change expressed concern about greenhouse warming at the highest levels of government and committed the United States to confront the issue. These documents recommend conducting the research necessary to understand the environmental behavior of biogenic greenhouse gases, of which carbon dioxide is the most significant. This research will lead toward the knowledge required to accurately project carbon removal rates from the atmosphere to the land biosphere and the oceans. This report presents a plan for large-scale U.S.-sponsored observations of CO₂ in the oceans and atmosphere. This plan represents an implementation plan for the CO₂ observations component of the CCSP. We recommend observations to track the fate of fossil fuel-derived CO₂, to characterize fluxes of CO₂ from the atmosphere to the land biosphere and oceans over large scales of space and time, and to achieve process-level understanding of physical and biological controls on those fluxes now and in the future. Complementary small-scale process studies of the land and ocean biospheres are needed for a comprehensive understanding of carbon fluxes and distributions. No specific recommendations for such programs are offered here, because they are being planned independently.

Abstract:

This introductory paper puts the technical articles to follow in the context of the need to understand gas transfer at water surfaces and to apply improved methods to the estimation of the exchange of gases between air and water. We summarize the physical and chemical background to processes of interfacial gas transfer, discuss field and laboratory approaches to measuring the gas exchange rate, and to elucidating its causes. Finally, we illustrate the application of acquired understanding in gas transfer to the global flux of carbon dioxide. This issue is of societal relevance in predicting and possibly reducing anthropogenic causes of climate change.

Abstract:

The transfer of gases across the air-water interface has received much attention over the past two decades, particularly in light of increased societal interest in the exchange of greenhouse gases and pollutants between natural water bodies and the atmosphere. Gas transfer at the interface between liquids and gases holds great fascination for a wide range of researchers, from fluid dynamicists to biogeochemists. However, the phenomena of gas transfer, and the problems we face in understanding them, involve daunting issues, including multi-phase flows over a wide range of spatial and temporal scales. Such complexity is increased by the presence of surface films of both natural and anthropogenic origin, which can modify the physical and chemical nature of the interface. As a result, the challenge of working on gas transfer has stimulated the development of multidisciplinary, collaborative efforts and the development of a variety of innovative experimental and observational techniques.

Abstract:

As part of the JGOFS field program, extensive CO₂ partial-pressure measurements were made in the atmosphere and in the surface waters of the equatorial Pacific from 1992 to 1999. For the first time, we are able to determine how processes occurring in the western portion of the equatorial Pacific impact the sea-air fluxes of CO₂ in the central and eastern regions. These eight years of data are compared with the decade of the 1980s. Over this period, surface-water pCO₂ data indicate significant seasonal and interannual variations. The largest decreases in fluxes were associated with the 1991-1994 and 1997-1998 El Niño events. The lower sea-air CO₂ fluxes during these two El Niño periods were the result of the combined effects of interconnected large-scale and locally forced physical processes: (1) development of a low-salinity surface cap as part of the formation of the warm pool in the western and central equatorial Pacific; (2) deepening of the thermocline by propagating Kelvin waves in the eastern Pacific; and (3) the weakening of the winds in the eastern half of the basin. These processes serve to reduce pCO₂ values in the central and eastern equatorial Pacific towards near-equilibrium values at the height of the warm phase of ENSO. In the western equatorial Pacific there is a small but significant increase in seawater pCO₂ during strong El Niño events (i.e., 1982-1983 and 1997-1998) and little or no change during weak El Niño events (1991-1994). The net effect of these interannual variations is a lower-than-normal CO₂ flux to the atmosphere from the equatorial Pacific during El Niño. The annual average fluxes indicate that during strong El Niños the release to the atmosphere is 0.2-0.4 Pg Cyr^-1 compared to 0.8-1.0 Pg Cyr^-1 during non-El Niño years.

Abstract:

During the recent GasEx-98 cruise in the North Atlantic aboard the NOAA ship Ronald H. Brown, carbon measurements were performed in the areas of 46°N, 20.5°W. This process study followed a warm core ring tagged with the deliberately introduced tracer, SF₆. Continuous surface water measurements were combined with vertical profiles sampled daily to depths up to 1000 m for carbon mass balance studies. Dissolved inorganic carbon (DIC) and fCO₂ measurements were conducted onboard in both underway and discrete analysis modes. During the 25-day experiment in the tagged patch surface water, fCO₂ values averaged 275 ± 9 µatm, providing a constant condition of undersaturation and flux of CO₂ into the ocean. Using the Wanninkhof (1992) exchange coefficient, the estimated CO₂ flux ranged from approximately 1-27 mol m^-2 yr^-1. The largest CO₂ flux occurred during a large wind event beginning on June 6. After the event, DIC and fCO₂ values decreased for a few days, as a result of increased productivity associated with the strong mixing event. The DIC results were combined with the TOC, TON, and nutrient data to provide a mass balance for carbon within the patch. The results for the 25-day period indicate DIC increases in the mixed layer ranging from 0.2-1.8 µmol kg^-1 d^-1 due to gas exchange.

Abstract:

Between 1991 and 1999, carbon measurements were made on 25 WOCE/JGOFS/OACES cruises in the Pacific Ocean. Investigators from 15 different laboratories and four countries analyzed at least two of the four measurable ocean carbon parameters (DIC, TAlk, fCO₂, and pH) on almost all cruises. The goal of this work is to assess the quality of the Pacific carbon survey data and to make recommendations for generating a unified data set that is consistent between cruises. Several different lines of evidence were used to examine the consistency, including comparison of calibration techniques, results from certified reference material analyses, precision of at-sea replicate analyses, agreement between shipboard analyses and replicate shore-based analyses, comparison of deep water values at locations where two or more cruises overlapped or crossed, consistency with other hydrographic parameters, and internal consistency with multiple carbon parameter measurements. With the adjustments proposed here, the data can be combined to generate a Pacific Ocean data set, with over 36,000 unique sample locations analyzed for at least two carbon parameters in most cases. The best data coverage was for DIC, which has an estimated overall accuracy of ~3 µmol kg^-1. TAlk, the second most common carbon parameter analyzed, had an estimated overall accuracy of ~5 µmol kg^-1. To obtain additional details on this study, including detailed crossover plots and information on the availability of the compiled, adjusted data set, visit the Global Data Analysis Project web site at http://cdiac.esd.ornl.gov/oceans/glodap.

Abstract:

Nitrate availability is generally considered to be the limiting factor for oceanic new production and this concept is central in our observational and modeling efforts. However, recent time-series observations off Bermuda and Hawaii indicate a significant removal of total dissolved inorganic carbon (C_T) in the absence of measurable nitrate. Here we estimate net carbon production in nitrate-depleted tropical and subtropical waters with temperatures higher than 20°C from the decrease in the salinity normalized C_T inventory within the surface mixed layer. This method yields a global value of 0.8 ? 0.3 petagrams of carbon per year (Pg C yr^-1, Pg = 10¹⁵ grams), which equates to a significant fraction (20-40%) of the recent estimates (20-4.2 Pg C yr^-1) of total new production in the tropical and subtropical oceans (Emerson et al., 1997; Lee, 2001). The remainder is presumably supported by upward flux of nutrients into the euphotic zone via eddy diffusion and turbulent mixing processes or lateral exchange. Our calculation provides the first global-scale estimate of net carbon production in the absence of measurable nitrate. We hypothesize that it is attributable to dinitrogen (N₂) fixing microorganisms, which can utilize the inexhaustible dissolved N₂ pool and thereby bypass nitrate limitation.

Abstract:

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Abstract:

A number of workers have recently shown that the thermodynamic constants for the dissociation of carbonic acid in seawater of Mehrbach et al. are more reliable than measurements made on artificial seawater. These studies have largely been confined to looking at the internal consistency of measurements of total alkalinity (TA), total inorganic carbon dioxide (TCO₂) and the fugacity of carbon dioxide (fCO₂). In this paper, we have examined the field measurements of pH, fCO₂, TCO₂, and TA on surface and deep waters from the Atlantic, Indian, Southern, and Pacific oceans to determine the pK₁, pK₂, and pK₂-pK₁. These calculations are possible due to the high precision and accuracy of the field measurements. The values of pK₂ and pK₂-pK₁ over a wide range of temperatures (-1.6-38°C) are in good agreement (within ±0.005) with the results of Mehrbach et al. The measured values of pK₁ at 4°C and 20°C are in reasonable agreement (within ±0.01) with all the constants determined in laboratory studies. These results indicate, as suggested by internal consistency tests, that the directly measured values of pK₁+pK₂ of Mehrbach et al. on real seawater are more reliable than the values determined for artificial seawater. It also indicates that the large differences of pK₂-pK₁ (0.05 at 20°C) in real and artificial seawater determined by different investigators are mainly due to differences in pK₂. These differences may be related to the interactions of boric acid with the carbonate ion. The values of pK₂-pK₁ determined from the laboratory measurements of Lee et al. and Lueker et al. at low fCO₂ agree with the field-derived data to ±0.016 from 5°C to 25°C. The values of pK₂-pK₁ decrease as the fCO₂ or TCO₂ increases. This effect is largely related to changes in the pK₂ as a function of fCO₂ or TCO₂. The values of fCO₂ calculated from an input of TA and TCO₂, which require reliable values of pK₂-pK₁, also vary with fCO₂. The field data at 20°C has been used to determine the effect of changes of TCO₂ on pK₂ giving an empirical relationship: pK₂^TCO2 = pK₂-1.6 x 10^-4 (TCO₂-2050) which is valid at TCO₂ > 2050 µmol kg^-1. This assumes that the other dissociation constants such as K_B for boric acid are not affected by changes in TCO₂. The slope is in reasonable agreement with the laboratory studies of Lee et al. and Lueker et al. (-1.2 x 10^-4 to -1.9 x 10^-4). This equation eliminates the dependence of the calculated fCO₂ on the level of fCO₂ or TCO₂ in ocean waters (σ = 29.7 µatm in fCO₂). An input of pH and TCO₂ yields values of fCO₂ and TA that are in good agreement with the measured values (±22.3 µatm in fCO₂ and ±4.3 µmol kg^-1 in TA). The cause of the decrease in pK₂ at high fCO₂ is presently unknown. The observed inconsistencies between the measured and computed fCO₂ values may be accounted for by adding the effect of organic acid (~8 µmol kg^-1) to the interpretation of the TA. Further studies are needed to elucidate the chemical reactions responsible for this effect.

Abstract:

During the GasEx-98 field campaign, observations of the upper ocean structure were performed to identify relationships between the fine thermohaline structure, turbulence, and gas exchange in the near-surface layer of the ocean. The upper ocean dynamics were then simulated using a one-dimensional mixed layer model with the mixing parameterization developed during the TOGA Coupled Ocean-Atmosphere Response Experiment (COARE). The model was initialized with the temperature, salinity, and velocity profiles in the upper 50 m thick layer of the ocean obtained from the conductivity-temperature-depth (CTD) and acoustic Doppler current profiler (ADCP) measurements and was forced with the air-sea heat and momentum fluxes measured by Edson et al. (1999). The model produced a set of parameters, including the time and depth dependent mixing coefficient and the depth of the mixed layer. The simulated mixed layer depth is consistent with the depth of the actively mixed layer determined from the turbulence profiles taken occasionally during GasEx-98 Leg 2 with a free-rising profiler. Moderate wind speed conditions prevailed during GasEx-98 Leg 2 with several storms and a few periods of calm weather. Both the modeling and experimental results demonstrate that under conditions of low wind speed, the surface-generated turbulence is constrained within a relatively thin surface layer of the ocean. In the near-surface layer, appreciable temperature, salinity, and gas concentration differences are formed because of diurnal warming or precipitation effects. These results are applied to the estimation of the effect of mixed layer processes on the bulk-flux formulation for the air-sea exchange of gases.

Abstract:

Based on about 940,000 measurements of surface-water pCO₂ obtained since the International Geophysical Year of 1956-1959, the climatological, monthly distribution of pCO₂ in the global surface waters representing mean non-El Niño conditions has been obtained with a spatial resolution of 4° × 5° for a reference year 1995. The monthly and annual net sea-air CO₂ flux has been computed using the NCEP/NCAR 41-year mean monthly wind speeds. An annual net uptake flux of CO₂ by the global oceans has been estimated to be 2.2 (+22% or 19%) Pg Cyr^-1 using the (wind speed)² dependence of the CO₂ gas transfer velocity of Wanninkhof (J. Geophys. Res. 97 (1992) 7373). The errors associated with the wind-speed variation have been estimated using one standard deviation (about ±2 m s^-1) from the mean monthly wind speed observed over each 4° × 5° pixel area of the global oceans. The new global uptake flux obtained with the Wanninkhof (wind speed)² dependence is compared with those obtained previously using a smaller number of measurements, about 250,000 and 550,000, respectively, and are found to be consistent within ±0.2 Pg Cyr^-1. This estimate for the global ocean uptake flux is consistent with the values of 2.0 ± 0.6 Pg Cyr^-1 estimated on the basis of the observed changes in the atmospheric CO₂ and oxygen concentrations during the 1990s (Nature 381 (1996) 218; Science 287 (2000) 2467). However, if the (wind speed)³ dependence of Wanninkhof and McGillis (Geophys. Res. Lett. 26 (1999) 1889) is used instead, the annual ocean uptake as well as the sensitivity to wind-speed variability is increased by about 70%. A zone between 40° and 60° latitudes in both the northern and southern hemispheres is found to be a major sink for atmospheric CO₂. In these areas, poleward-flowing warm waters meet and mix with the cold subpolar waters rich in nutrients. The pCO₂ in the surface water is decreased by the cooling effect on warm waters and by the biological drawdown of pCO₂ in subpolar waters. High wind speeds over these low pCO₂ waters increase the CO₂ uptake rate by the ocean waters. The pCO₂ in surface waters of the global oceans varies seasonally over a wide range of about 60% above and below the current atmospheric pCO₂ level of about 360 µatm. A global map showing the seasonal amplitude of surface-water pCO₂ is presented. The effect of biological utilization of CO₂ is differentiated from that of seasonal temperature changes using seasonal temperature data. The seasonal amplitude of surface-water pCO₂ in high-latitude waters located poleward of about 40° latitude and in the equatorial zone is dominated by the biology effect, whereas that in the temperate gyre regions is dominated by the temperature effect. These effects are about six months out of phase. Accordingly, along the boundaries between these two regimes, they tend to cancel each other, forming a zone of small pCO₂ amplitude. In the oligotrophic waters of the northern and southern temperate gyres, the biology effect is about 35 µatm on average. This is consistent with the biological export flux estimated by Laws et al. (Glob. Biogeochem.Cycles 14 (2000) 1231). Small areas such as the northwestern Arabian Sea and the eastern equatorial Pacific, where seasonal upwelling occurs, exhibit intense seasonal changes in pCO₂ due to the biological drawdown of CO₂.

Abstract:

Gas transfer velocities are frequently related to wind speeds in order to estimate air-sea gas fluxes on regional and global scales. Since the gas exchange-wind speed relationships are non-linear, the wind speed distribution will have an effect on the fluxes if time-averaged winds are used. Commonly, a Weibull distribution is assumed for monthly or yearly averaged wind speeds. Although this is a reasonable assumption for global winds, significant regional deviations from this distribution exist. For areas with steady winds such as the trade wind regions and Westerlies in the Southern Ocean, the Weibull assumption will overestimate the long-term gas transfer velocities. Using regional wind speed distribution patterns based on 6-hour NCEP re-analysis winds instead of a Weibull distribution, the global oceanic CO₂ uptake estimate decreases by 5% if a quadratic dependence with wind speed is assumed and by 26% if a cubic dependence of gas exchange with wind speed is used.

Abstract:

A method for preserving natural water samples for dissolved oxygen analysis is recommended. The conventional method of using greased glass stoppers has been found to cause a 12% increase in oxygen concentration over a one-month period as a result of evaporation of water sample through micro-gaps and concurrent intrusion of air into the water sample bottles. Sealing the sample bottles with water has been found to be the optimal storage method. It permits a 100.2 ? 0.3% recovery of dissolved oxygen concentration from storage seawater samples over four months.

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Abstract:

During a Lagrangian deliberate tracer study in the North Atlantic, the 1998 Gas Exchange Experiment (GASEX-98), hourly measurements of wind speed, sea surface temperature, fCO₂, and fluorescence were made from two carbon interface ocean atmosphere (CARIOCA) drifting buoys in a warm-core eddy near 46°N and 21.5°W over a period of approximately 20 days. Shipboard measurements of fCO₂ near the buoys were used to verify the buoy operation, calibrate the buoy measurements, and assess the performance of the fCO₂ sensor. The strong air-sea fCO₂ gradient in the eddy and intense atmospheric forcing during the experiment provided ideal conditions for demonstrating the potential of autonomous drift buoy measurements for studies of surface ocean biogeochemistry, where changes of fCO₂ were rapid and large. During the experiment, a storm occurred with wind speeds reaching as high as 16-17 m s^-1, leading to a sharp decrease in sea surface temperature and an increase in fCO₂ of ~30 µatm. The magnitude of this sudden change in fCO₂ is equal to approximately half of the annual range of fCO₂ in this area. The air-sea flux estimate for the ~20 day experiment using the Wanninkhof (1992) gas transfer velocity formulation was -0.012 mol m^-2 d^-1 and using the Liss and Merlivat (1986) formulation was -0.007 mol m^-2 d^-1. The storm event, lasting three to four days, accounted for ~38% of the flux over this period. Approximately 16 hours after the onset of the storm, there was an increase in surface fluorescence coincident with the initial increase in fCO₂. Nitrate measurements made from the ship in the eddy show a sharp peak in surface concentrations ~24 hours after the increase in winds and ~6-8 hours after the increase in surface fluorescence. After the upwelling of the NO₃ the fluorescence increases more sharply while the fCO₂ decreases, consistent with biological productivity. The surface fluorescence measurements remain higher than prestorm conditions for ~5 days after the NO₃ has disappeared.

Abstract:

A comprehensive study of air-sea interactions focused on improving the quantification of CO₂ fluxes and gas transfer velocities was performed within a large open ocean CO₂ sink region in the North Atlantic. This study, GasEx-98, included shipboard measurements of direct covariance CO₂ fluxes, atmospheric CO₂ profiles, atmospheric DMS profiles, water column mass balances of CO₂, and measurements of deliberate SF₆^-3He tracers, along withair-sea momentum, heat, and water vapor fluxes. The large air-sea differences in partial pressure of CO₂ caused by a springtime algal bloom provided high signals for accurate CO₂ flux measurements. Measurements were performed over a wind speed range of 1-16 m s^-1 during the three-week process study. This first comparison between the novel air-side and more conventional water column measurements of air-sea gas transfer show a general agreement between independent air-sea gas flux techniques. These new advances in open ocean air-sea gas flux measurements demonstrate the progress in the ability to quantify air-sea CO₂ fluxes on short time scales. This capability will help improve the understanding of processes controlling the air-sea fluxes which, in turn, will improve our ability to make regional and global CO₂ flux estimates.

Abstract:

This document contains data and metadata from a zonal cruise along nominally 24.5°N in the Atlantic Ocean from Las Palmas, Canary Islands in Spain to Miami, Florida. The cruise took place from January 23 to February 24, 1998 aboard the NOAA Ship Ronald H. Brown under auspices of the National Oceanic and Atmospheric Administration (NOAA). This report presents the analytical and quality control procedures performed during the cruise and bottle data from the cruise. The research was sponsored by the NOAA Climate and Global Change Program under: (i) The Ocean-Atmosphere Carbon Exchange Study (OACES); and (ii) the World Ocean Circulation Experiment (WOCE) repeat hydrography program. Samples were taken from up to 36 depths at 130 stations. The data presented in this report includes the analyses of water samples for: salinity, nutrients, total dissolved inorganic carbon dioxide (DIC), fugacity of carbon dioxide (fCO₂), total alkalinity (TA), pH, total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), chlorofluorocarbons, and stable carbon isotopic ratio of DIC (¹³C/¹²C). Basic hydrographic parameters, pressure, CTD salinity, temperature and the calculated potential temperature, and potential density are included as well.

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No abstract.

Abstract:

A diurnal study in an anticyclonic eddy provides the first evidence of nutrient dynamics consistent with the observed trends in solar radiation, oxygen concentration changes, and estimates of the eddy diffusive flux of nitrate from nitracline. A new production rate of 24 mmol C m^-2 d^-1 was determined from nitrate inventory changes at nM levels in the mixed layer using a liquid waveguide technique combined with eddy diffusion estimates across the base of the mixed layer from temporal changes in the vertical penetration of SF₆. The new production supported by nitrate from deepening of the mixed layer after storm events is two times larger than that from the daily diffusive flux. Our results demonstrate that new production in the oligotrophic ocean can be enhanced by a supply of nitrate through the eddy turbulence-induced diffusive flux and entrainment during storms.

Abstract:

A coherent representation of carbonate dissociation constants and measured inorganic carbon species is essential for a wide range of environmentally important issues such as oceanic uptake of anthropogenic CO₂ and carbon cycle depictions in ocean circulation models. Previous studies have shown varying degrees of discordance between calculated and measured CO₂-system parameters. It is unclear if this is due to errors in thermodynamic models or in measurements. In this work, we address this issue using a large field data set (15,300 water samples) covering all ocean basins. Our field data, obtained using laboratory-calibrated measurement protocols, are most consistent with calculated parameters using the dissociation constants of Mehrbach et al. (1973) as refit by Dickson and Millero (1987). Thus, these constants are recommended for use in the synthesis of the inorganic carbon data collected during the global CO₂ survey during the 1990s and for characterization of the carbonate system in seawater.

Abstract:

High quality total inorganic carbon (C_T) measurements made in the major ocean basins as part of the Joint Global Ocean Flux Study (JGOFS), the National Oceanic and Atmospheric Administration/Ocean Atmosphere Carbon Exchange Study (NOAA/OACES), and the Department of Energy/World Ocean Circulation Experiment (DOE/WOCE) programs are related to sea surface temperature (SST) and nitrate (NO₃^-).A simple two-parameter function with SST and NO₃^- of the form NC_T = a + b SST + c SST² + d NO₃^- fits salinity (S)-normalized surface C_T (NC_T = C_T × 35/S) data for different parts of the oceans within an area-weighted error of ±7 µmol kg^-1 (1 sigma). Estimated values of NC_T using the derived algorithms with NO₃^- and SST are compared with values calculated from the surface partial pressure of CO₂ (pCO_2SW) (Takahashi et al., 1997) and total alkalinity (A_T) (Millero et al., 1998) fields using thermodynamic models. Comparisons of the estimated values of NC_T with measurements not used to derive the same algorithms, and comparisons with the values calculated from global A_T and pCO_2SW fields, give a realistic uncertainty of ±15 µmol kg^-1 in estimated C_T. The derived correlations of NC_T with SST and NO₃^- presented here make it possible to estimate surface C_T over the ocean from climatological SST, S, and NO₃^- fields.

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No abstract.

Abstract:

Improved estimates of the variability in air-sea CO₂ fluxes on seasonal and interannual time scales are necessary to help constrain the net partitioning of CO₂ between the atmosphere, oceans, and terrestrial biosphere. Few direct measurements of the carbon system have been made in the main Indian Ocean basin. In the mid 1990s, several global carbon measurement programs focused on the Indian Ocean, greatly increasing the existing carbon database for this basin. This study examines the combined surface CO₂ measurements from three major U.S. programs in the Indian Ocean: the global carbon survey cruises, conducted in conjunction with the World Ocean Circulation Experiment (WOCE); the NOAA Ocean-Atmosphere Carbon Exchange Study (OACES) Indian Ocean survey; and the Joint Global Ocean Flux Study (JGOFS) Arabian Sea Process Study. These data are fit with multiparameter linear regressions as a function of commonly-measured hydrographic parameters. These fits are then used with NCEP/NCAR reanalysis and Levitus 94 gridded values to evaluate the seasonal variability of surface seawater CO₂ in the tropical and subtropical Indian Ocean and to estimate the magnitude of the Indian Ocean as a net sink for atmospheric CO₂. The net annual flux for the Indian Ocean (north of 36°S) was -12.4 ± 0.5 × 10¹² mol of carbon (equivalent to -0.15 Pg C) in 1995. The relatively small net flux results from the very different surface water pCO₂distributions and seasonal variations in the northern and southern Indian Ocean. The equatorial and northern hemisphere regions have values that are generally above atmospheric values. During the southwest monsoon, pCO₂ values in the Arabian Sea coastal upwelling region are among the highest observed in the oceans. The upwelling is seasonal in nature, however, and only affects a relatively small area. The Indian Ocean equatorial region generally has values slightly above atmospheric. Unlike the Pacific and Atlantic Oceans, however, no clear equatorial upwelling signature was observed in 1995. The Southern Hemisphere Indian Ocean, which represents the largest region by area, generally has values below atmospheric. The strongest undersaturations are observed in the austral winter, with summer values reaching near or slightly above atmospheric.

Abstract:

New production can be estimated from accurate measurements of inventory change in nitrate at nM levels in the photic zone. A strong diel cycle was observed in nitrate concentrations in response to photosynthesis in the eastern North Atlantic during the GASEX-98 cruise. During a diel study, nitrate concentration was 92 nM in the morning and decreased to 12 nM by 6 p.m. It increased after dark, presumably due to the diffusive flux from the nitracline. Oxygen showed a similar diel cycle with a change in concentration of about 2 µM. The vertical eddy diffusivity was derived from temporal changes in concentrations of a deliberate tracer, SF6, below the mixed layer. Together with vertical nitrate distributions, the nitrate flux from nitracline throughout the nighttime can account for a nitrate concentration of 102 nM by morning, which is in good agreement with measured nitrate of 92 nM at 6 a.m. The new production estimated from changes of nitrate inventory in the photic zone during the day was 28 mmole C/m² d. Increases in the mixed layer nitrate were observed during storm events that deepened the mixed layer and brought the nitrate to the surface. The storm-induced nitrate disappeared within two days, indicating a rapid uptake by phytoplankton. The relative importance of sporadic storm events versus daily diffusive flux in supply nitrate to new production can be estimated based on nitrate inventory changes in the photic zone.

Abstract:

In order to determine the seasonal and interannual variability of the CO₂ released to the atmosphere from the equatorial Pacific, we have developed pCO₂-temperature relationships based upon shipboard oceanic CO₂ partial pressure measurements, pCO₂, and satellite sea surface temperature, SST, measurements. We interpret the spatial variability in pCO₂ with the help of the SST imagery. In the eastern equatorial Pacific, at 5°S, pCO₂ variations of up to 100 µatm are caused by undulations in the southern boundary of the equatorial upwelled waters. These undulations appear to be periodic with a phase and a wavelength comparable to tropical instability waves, TIW, observed at the northern boundary of the equatorial upwelling. Once the pCO₂ signature of the TIW is removed from the Alize II cruise measurements in January 1991, the equatorial pCO₂ data exhibit a diel cycle of about 10 µatm with maximum values occurring at night. In the western equatorial Pacific, the variability in pCO₂ is primarily governed by the displacement of the boundary between warm pool waters, where air-sea CO₂ fluxes are weak, and equatorial upwelled waters which release high CO₂ fluxes to the atmosphere. We detect this boundary using satellite SST maps. East of the warm pool, DELTA-P is related to SST and SST anomalies. The 1985-1997 CO₂ flux is computed in a 5° wide latitudinal band as a combination of DELTA-P and CO₂ exchange coefficient, K, deduced from satellite wind speed, U. It exhibits up to a factor 2 seasonal variation caused by K-seasonal variation and a large interannual variability, a factor 5 variation between 1987 and 1988. The interannual variability is primarily driven by displacements of the warm pool that makes the surface area of the outgassing region variable. The contribution of DELTA-P to the flux variability is about half of the contribution of K. The mean CO₂ flux computed using either the Liss and Merlivat (1986) or the Wanninkhof (1992) K-U parameterization amounts to 0.11 GtC yr^-1 or to 0.18 GtC yr^-1, respectively. The error in the integrated flux, without taking into account the uncertainly on the K-U parameterization, is less than 31%.

Abstract:

No abstract.

Abstract:

The interannual variability of the CO₂ partial pressure(pCO₂) in the surface layer of the east equatorial Pacific Ocean near 100°W is studied and compared with the seasurface temperature (SST) monitored from satellites. This variability is shown to be correlated with the SST anomaly rather than with the temperature itself. The pCO_2OC variability is related to the variability of the upwelling systems (the equatorial upwelling and the upwelling along the American coast), the main influence being from the coastal upwelling via the surface water advected from the east. A method is derived to interpolate the pCO_2OC measurements using the SST satellite measurements. By combining the result with the exchange coefficient (K) deduced from the wind speed provided by satellite-borne instruments, we deduce the air-sea CO₂ flux and, for the first time, we continuously monitor its temporal variation. The variability of this flux is mainly due to the variability of K, with a clear seasonal variation. The flux obtained using the Liss and Merlivat (1986) relationship averaged from April 1985 to June 1997 in the region 97.5°-107.5°W, 0-5°S is 1.67 mole m^-2 yr^-1 of CO₂, leaving the ocean with an estimated accuracy of 30%.

Abstract:

As a collaborative program to measure global ocean carbon inventories and provide estimates of the anthropogenic CO₂ uptake in the oceans, the National Oceanic and Atmospheric Administration, the U.S. Department of Energy, and the National Science Foundation have co-sponsored the collection of ocean carbon measurements as part of the World Ocean Circulation Experiment (WOCE) and Ocean-Atmospheric Carbon Exchange Study (OACES). The cruises discussed here occurred in the North and South Pacific from 1990 through 1996. The new estimates for anthropogenic CO₂, employing the Δ-C* method of Gruber et al. (1996), indicate that the largest buildup of anthropogenic CO₂ occurs in subtropical waters. Along 155°W, anthropogenic CO₂ penetrates to a maximum depth of 900 m at about 37°N in the North Pacific and 1300 m at about 48°S in the South Pacific. Strong shoaling of anthropogenic CO₂ occurs southward of 50°S and northward of 48°N. The anthropogenic CO₂ inventories from the observations are smaller than the Princeton Ocean Biogeochemical Model (POBM) model estimates, primarily because the Princeton model produces too much deep convective mixing of anthropogenic CO₂ in the Southern Ocean.The NCAR Climate System Ocean model, which has very different physics and biological parameterizations, appears to do a better job of reproducing the general patterns in the data-based section.

Abstract:

As a collaborative program to measure global ocean carbon inventories and provide estimates of the anthropogenic carbon dioxide (CO₂) uptake by the oceans, the National Oceanic and Atmospheric Administration and the U.S. Department of Energy have sponsored the collection of ocean carbon measurements as part of the World Ocean Circulation Experiment and Ocean-Atmosphere Carbon Exchange Study cruises. The cruises discussed here occurred in the North and South Pacific from 1990 through 1996. The carbon parameters from these 30 crossover locations have been compared to ensure a consistent global data set emerges from the survey cruises. The results indicate that for dissolved inorganic carbon, fugacity of CO₂, and pH, the agreement at most crossover locations are well within the design specifications for the global CO₂ survey, whereas in the case of total alkalinity, the agreement between crossover locations is not as close.

Abstract:

The equatorial ocean is an important CO₂ source to the atmosphere, contributing annually 0.7-1.5 Pg of carbon as CO₂, as much as 80% of which is attributed to the equatorial Pacific. This source is known to change significantly by ENSO events. To better understand the regional and interannual variability of CO₂ fluxes from the equatorial Pacific, field measurements of the partial pressure of CO₂ (pCO₂) have been made in the equatorial Pacific region since 1992. Here, we report that during the 1991-1994 ENSO period the net annual sea-to-air flux of CO₂ was 0.3 PgC from the fall of 1991 to the fall of 1992, 0.6 PgC in 1993, and 0.7 PgC in 1994. These fluxes are 30%-80% of the 0.9 PgC observed during the non-El Niño year of 1996. The total reduction of the sea-to-air CO₂ flux during the 1991-1994 El Niño is estimated to be 0.8-1.2 PgC, which accounts for 16-36% of the atmospheric anomaly (the difference between the annual atmospheric CO₂ increase in PgC yr^-1 and the long-term average increase of 3.18 PgC yr^-1) observed over the same period.

Abstract:

A program for repeated sampling of tracers and variables essential for quantitative understanding of the carbon cycle is recommended within CLIVAR/GOOS. The program is critical to our monitoring and understanding of climate change, both natural and anthropogenic. The objectives are: quantification of changes in the rates and spatial patterns of oceanic carbon uptake, fluxes, and storage of anthropogenic CO₂; detection and possible quantification of changes in water mass renewal and mixing rates; and provision of a stringent test of the time integration of models' natural and anthropogenic climate variability. The strategy is to put in place a global observing network for tracers and CO₂ to document the continuing large-scale evolution of these fields. Hydrographic lines are advocated, although it is realized that there has to be a limit on these observations due to logistical and resource constraints. Thus, there is the need to supplement these observations with time series and autonomous measurements to provide detail in the temporal evolution of the fields.

Abstract:

A general description of the current approaches for measuring trace gas fluxes in aquatic and terrestrial systems is presented in this paper. Our aim is to provide an overview of the current methodologies employed in trace gas flux measurements and the most recent advancements made; with emphasis on the uncertainties observed and potential areas for future developments required to further minimize these uncertainties brought about by spatial and temporal variabilities of fluxes in the field. The increase in sensitivity and improved response time of analytical devices for measuring trace gases within the last five years, such as advancements in laser spectroscopy, have significantly improved the effectiveness of the current methods of measuring these gases in aquatic and terrestrial systems. Systematic errors in trace gas flux estimates have also been reduced with the refinements in estimates of the gas transfer velocity, k, through the use of tracers in the two systems. Footprint corrections of micrometeorological flux measurements in terrestrial systems have provided a better means of identifying the spatial sources of trace gases, and thus, have increased the scope of inference from trace gas flux measurements. Despite these improvements, however, flux measurement errors still remain high. Experimental and sampling designs that can efficiently and effectively deal with the spatial and temporal variabilities in trace gas flux measurements to the minimum are of utmost priority. The same can be said of the modeling procedures; that is, there is a need for an effective method that can reduce instead of propagate potential errors in scaling from field plot to regional or global scales.

Abstract:

No abstract.

Abstract:

No abstract.

Abstract:

To date, large uncertainties in the extent of the CO₂ flux between the atmosphere and ocean have prevented us from accurately quantifying how the increasing atmospheric CO₂ burden partitions between the ocean and the terrestrial biosphere. This limits our ability to accurately predict future atmospheric CO₂ levels. We have recently designed a direct CO₂ flux measurement system that considerably improves our estimates of air-sea gas exchange. The system measures the direct air-sea flux of CO₂ in the atmospheric boundary layer using eddy correlation (direct covariance). It was successfully deployed during the large scale experiment to study air-sea gas fixes, GASES98, which was conducted in the CO₂ sink region of the North Atlantic during May/June of 1998. The seasonal algal bloom caused air-sea pCO₂ differences of between -80 to ~100 µatm. This large concentration gradient generated large signals for accurate measurement of the CO₂ flux using a close path CO₂ sensor. In addition to the CO₂ gas flux, the comprehensive atmospheric flux measurement suite included momentum, heat, and moisture fluxes. Atmospheric flux and air-sea gas concentration measurements were performed for over 500 hours, providing more than 1000 observations. Wind speeds between 1 and 16 m/s were experienced over the range of these observations. Preliminary flux estimates from our system compare extremely well with previous estimates of the gas transfer velocity for wind speeds below 7 m/s. At higher wind speeds, the transfer velocities obtained from our system are as much as 20-50% higher than those estimated by empirical relationships. Based on accurate air-sea CO₂ coefficients obtained by our investigation and atmospheric and surface ocean pCO₂ data obtained to date, estimates of the global ocean CO₂ sink are now feasible. Our findings will also provide better predictions of the seasonal and interannual variability of sea-air CO₂ flux observed in various global regions.

Abstract:

Results of total dissolved inorganic carbon (DIC) and total alkalinity (TA) measurements made in the East China Sea (ECS) during a geochemical expedition of KEEP (Kuroshio Edge Exchange Processes) program in May of 1996 show that ECS is a CO₂ sink during the spring season. The mean difference of fCO₂ (fugacity of CO₂) between the atmosphere and surface water is calculated to be 28 µatm, and the resulting net CO₂ invasion flux is 2.1 mol/m²/yr, which gives about 0.03 GtC/yr of CO₂ uptake in this continental shelf in spring. This study supports the notion that shelf regions can be a significant CO₂ sink. The riverine alkalinity, which discharges into ECS, is estimated to be 1,743 µmol/kg on the basis of a linear relationship between TA and salinity. The observed salinity-normalized alkalinity in ECS is higher than that in the open sea, and this excess alkalinity is estimated to be 42 µmol/kg. With the known rate of the Changjiang discharge, this excess TA gives a mean residence time of 1.2 years for the continental shelf water in the ECS. The DIC in the ECS is also found to be higher than that in the open sea. This excess DIC is estimated to be about 76 ± 70 µmol/kg, which is equal to a net carbon input to ECS of 3.9 ± 3.6 mol/m²/yr. Based on the riverine alkalinity input, the equivalent riverine carbon flux from Changjiang discharge is estimated to be about 1.8 mol/m²/yr. With a net CO₂ invasion flux of 2.1 ± 2.8 mol/m²/yr, the remaining 0 ± 4.6 mol/m²/yr could come from remineralization of organic matter derived from the biological pump in the shelf or terrestrial sources. Although this preliminary carbon budget implies that gas exchange and riverine input are the main sources of excess carbon in ECS, the contribution of biological carbon flux can not be ruled out because of the large uncertainty associated with these estimates.

Abstract:

No abstract.

Abstract:

Uncertainties in inverse calculations to determine regional carbon fluxes between the atmospheric, oceanic, and terrestrial reservoirs (Fan et al., 1998) have clearly indicated the need to improve our oceanic carbon flux estimate. There have been significant advances in several aspects of air-sea flux determinations to address this question, including direct estimates of fluxes by co-variance and gradient measurements in the air-boundary layer, extrapolation routines using remote sensing products, and a rapidly increasing observational database of air-sea partial pressure differences. The gas fluxes are commonly expressed as F = k s Δ-pCO₂ where F is the air-sea flux CO₂ (mol m^-2 day^-1), k is the gas transfer velocity (m day^-1), s is the solubility (mol m³ µatm^-1), and Δ-pCO₂ is th eair-water partial pressure difference (µatm). This overview discusses recent research aimed at improving estimates of F, k, and Δ-pCO₂.

Abstract:

Using recent laboratory and field results we explore the possibility of a cubic relationship between gas exchange and instantaneous (or short-term) wind speed, and its impact on global air-sea fluxes. The theoretical foundation for such a dependency is based on retardation of gas transfer at low to intermediate winds by surfactants, which are ubiquitous in the world's oceans, and bubble-enhanced transfer at higher winds. The proposed cubic relationship shows a weaker dependence of gas transfer at low wind speed and a significantly stronger dependence at high wind speed than previous relationships. A long-term relationship derived from such a dependence, combined with the monthly CO₂ climatology of Takahashi (1997), leads to an increase in the global annual oceanic CO₂ uptake from 1.4 Gigaton C yr^-1 to 2.2 Gigaton C yr^-1. Although a cubic relationship fits within global bomb-¹⁴C oceanic uptake constraints, additional checks are warranted, particularly at high wind speeds where the enhancement is most pronounced.

Abstract:

In many numerical ocean chemistry models total dissolved inorganic carbon (DIC) and total alkalinity (TA) are transported between subsurface boxes, and partial pressure pCO₂ is calculated from TA and DIC in the surface box in order to account for air-sea exchange of carbon dioxide. The conversion is commonly performed by solving the thermodynamic relationships for equilibria between carbonate, bicarbonate, and aqueous CO₂ using apparent carbonate dissociation constants. Four independent determinations of the constants have been performed for seawater in the past 50 years. These results have been corrected, refit, and combined by others, creating a virtual cottage industry of laboratory and field verification and cross checks. Here we show that, based on extensive field observations in three major ocean basins, the calculated surface pCO₂ from TA and DIC corresponds best with the measured pCO₂ of the constants proposed by Mehrbach et al.

Abstract:

A comparison of different methods of estimating anthropogenic CO₂ into the Atlantic Ocean through the center of the basin between 62°N and 42°S is performed using referenced high quality total dissolved inorganic carbon (DIC) data. The specific anthropogenic input is determined utilizing analytical procedures as described in Gruber et al. (1996), and Chen and Millero (1979) to correct for remineralization and to estimate preanthropogenic endmembers. These estimates are compared with results of the Princeton ocean biogeochemical model (OBM). The results show the specific inventories of anthropogenic carbon agreeing to within 20% but with different uptake patterns. The differences are largely caused by differing assumptions about mixing and winter outcrop endmembers. The same photosynthetic quotients (Redfield ratios) were used each methods. Varying these constants within the range of literature values causes changes in specific inventories of similar magnitude as the different methodologies. Comparison of anthropogenic CO₂ uptake and chlorofluorocarbon ages, and preanthropogenic photosynthetic quotients utilizing the analytical methods suggest that anthropogenic CO₂ penetration is too shallow following the procedure according to Gruber et al. (1996), and too deep using those of Chen and Millero (1979) in the North Atlantic. The results support previous observations that the uptake of CO₂ in the North Atlantic is disproportionate to its surface area. This is caused by a combination of deep water formation and deep winter mixed layers.

Abstract:

For air-water gas exchange across unbroken surfaces, the only gas-dependent parameter affecting the transfer velocity is the molecular diffusivity of the transferring species. In contrast, bubble-mediated transfer processes can cause the transfer velocity to depend on both molecular diffusivity and aqueous-phase solubility. This can complicate the analysis of data from dual-gaseous tracer gas transfer experiments. Bubble effects also complicate the estimation of transfer velocities for other gases from the transfer velocity calculated using the dual-tracer data. Herein, a method for incorporating the effects of bubble-mediated gas transfer processes on the transfer velocity is presented. This new procedure is used to analyze the data from two recent dual-tracer gas transfer experiments. Transfer velocities that include the effect of bubbles are calculated using the data from two previous oceanic dual-gaseous tracer experiments. Comparing these transfer velocities with transfer velocities calculated by neglecting the effect of bubbles shows that bubble-mediated transfer increased the transfer velocity of helium 3 by 5% at a wind speed of 10.6 m s^-1. However, when using the transfer velocities form helium 3 to calculate transfer velocities for carbon dioxide under the same conditions, including the effect of bubbles, decreases the transfer velocity of carbon dioxide by 18%. This shows that bubble-mediated transfer does not have a large effect on the analysis of dual-tracer data, but it is important in relating transfer velocities determined using helium 3 and sulfur hexafluoride to transfer velocities of more soluble gases at wind speeds above 10 m s^-1.

Abstract:

This paper provides a review of the physics and chemistry associated with air-sea gas transfer of transient atmospheric trace gases and the available laboratory and field measurement techniques used to study air-water gas transfer. The mechanistic principals and their relation to the measurement techniques are used to show that the error associated with estimating air-sea transfer velocities of transient tracers from transfer velocities measured using proxy tracers can be significant if an incorrect dependence of the transfer velocity on molecular diffusivity is assumed. Bubble-mediated transfer processes are also demonstrated to have a significant effect on the parameterization of the transfer velocity.

Abstract:

From July 4-August 30, 1993, the National Oceanic and Atmospheric Administration's (NOAA) Ocean-Atmosphere Carbon Exchange Study (OACES) and Radiatively Important Trace Species (RITS) programs participated in an oceanographic research cruise aboard the NOAA ship Malcolm Baldrige. The objectives of the OACES component were to determine the source and sink regions of CO₂ in the equatorial and North Atlantic during the summer and to establish a baseline of total carbon inventory in the region. Data were collected from 5°S to Iceland along a nominal longitude of 20°W. This report presents only the OACES-related data from legs 1, 2A, and 2B, including hydrography, nutrients, carbon species, dissolved oxygen, total inorganic carbon, chlorofluorocarbons, total alkalinity, pH, and salinity. Included are contour plots of the various parameters and descriptions of the sampling techniques and analytical methods used in data collection.

Abstract:

The chlorofluorocarbon CFC-12 (CCl₂-F₂) distributions from two occupations of a meridional hydrographic section in the eastern North Atlantic are used to describe the oceanic penetration of CFCs and change in the integrated ventilation patterns over the five years from 1988 to 1993. The CFC-12 water-column inventories increased by 30-40%, despite a slowing atmospheric growth rate (14%), because of continuing uptake by undersaturated subsurface water masses whose response is lagged by the ventilation time-scales. After removing the long-term CFC temporal trend using a tracer age based normalization technique, we observe a distinct dipole pattern in upper ocean ventilation, with reduced convection in the subpolar gyre and enhanced production of saline subtropical underwater in 1993. These differences are discussed in relation to interannual variability in atmospheric surface forcing, upper ocean anomalies, and convection patterns associated with the North Atlantic Oscillation.

Abstract:

We have developed a new temperature-controlled, automated underway system for making atmospheric and surface ocean pCO₂ measurements onboard research vessels equipped with an uncontaminated seawater intake system. Uncontaminated seawater is supplied to a showerhead plexiglass equilibrator at the rate of approximately 50 liters/minute. After about 3 minutes, the air trapped in the equilibrator is equilibrated with seawater. This air is sampled six times per hour. In addition, atmospheric air is sampled three times per hour from the intake on the bow flagstaff through 3/8" Dekabon^TM tubing to the underway system. The CO₂ measurements are made with a differential, non-dispersive, infrared analyzer LiCor^TM (model 6252). The underway system operates on an hourly cycle with the first quarter of each hour devoted to calibration with three CO₂ standards, each measured for 5 minutes. A second order polynomial calibration curve is calculated from the voltage values of the standards. The remaining time in each hour is used to measure equilibrator air (15 min), bow air (15 min), and equilibrator air once again (15 min). To date, we have successfully used the underway pCO₂ system on 12 cruises of the NOAA Ship Ka'imimoana in the equatorial Pacific. The analytical precision of the system is approximately 0.3-0.4 ppm for seawater and for air.

Abstract:

An improved understanding of the partitioning of carbon between the atmosphere, terrestrial biosphere, and ocean allows for more accurate predictions of future atmospheric CO₂ concentrations under various fossil-fuel CO₂ emission scenarios. One of the more poorly quantified relevant processes is the interannual variability in the uptake of fossil-fuel CO₂ from the atmosphere by the terrestrial biosphere and ocean. Existing estimates, based on atmospheric measurements, indicate that the oceanic variability is large. Here we estimate the interannual variability in global net air-sea CO₂ flux using changes in the observed wind speeds and the partial pressure of CO₂ (pCO₂) in surface seawater and the overlying air. Changes in seawater pCO₂ are deduced from interannual anomalies in sea surface temperature and the regionally and seasonally varying temperature-dependence of seawater pCO₂, assuming that variations in sea surface temperature reflect seawater pCO₂ changes caused by thermodynamics, biological processes, and water mixing. The calculated interannual variability in oceanic CO₂ uptake of 0.4 Gt C yr^-1(2 sigma) is much less than that inferred from the analysis of atmospheric measurements. Our results suggest that variable sequestration of carbon by the terrestrial biosphere is the main cause of observed year-to-year variations in the rate of atmospheric CO₂ accumulation.

Abstract:

The NOAA Equatorial Pacific CO₂ system data set (~2500 water samples) has been evaluated to assess the internal consistency of measurements and calculations involving CO₂ fugacity and pH_T. This assessment represents the first large scale field comparison of pH_T and fCO₂ data. Comparisons of direct discrete CO₂ fugacity (fCO₂) measurements with CO₂ fugacity calculated from total inorganic carbon (C_T), total alkalinity (A_T), and spectrophotometric pH (pH_T = -log[H⁺]_T) indicate that a variety of improvements are needed in the parameter measurements and thermodynamic relationships used to relate fCO₂, C_T, A_T, and pH_T in seawater. CO₂ fugacity calculated from C_T and pH_T or A_T and pH_T agree with direct measurements to no better than 1%. Comparisons of measured fugacity, fCO₂ (measured), and CO₂ fugacity calculated from C_T and pH_T, fCO₂ (C_T, pH_T), indicate that the precision of fCO₂ calculations is good relative to direct measurements. In contrast, due to the extreme sensitivity of fCO₂ and [H⁺]_T calculations to relatively small errors in both C_T and A_T, CO₂ fugacity, as well as [H⁺]_T, calculated from C_T and A_T are very imprecise and render comparisons with direct measurements of little use. Consequently, precise calculations of fCO₂ require the use of direct pH_T measurements.

Abstract:

Assessments of ocean carbon uptake using the air-sea disequilibrium of CO₂ require very high quality measurements of pCO₂ in the atmosphere and in surface seawater. These measurements are often collected and analyzed using infrared detectors. Laboratory data are presented here which suggest that errors of the order of several parts per million in xCO₂ can result if the analyzer temperature and pressure are not carefully matched during calibration and sampling. Field data were examined to address questions about the importance of measuring analysis temperature and pressure under more extreme conditions, sample averaging, and calibration frequency. The results indicate that calibration frequency can be minimized without significant compromises in data quality if the analyzer temperatures and pressures are suitably monitored and/or controlled. Daily calibrations gave results to within 0.4 ppm of the results obtained by hourly calibration when the temperature of the analyzer was controlled to ±0.2°C and the voltages were corrected for pressure differences between calibration and sampling.

Abstract:

This document contains data and metadata from the I8 repeat cruise in the Indian Ocean cruise in 1995 from Fremantle, Australia to Male in the Maldives. From September 22 to October 25, 1995, the National Oceanic and Atmospheric Administration (NOAA) sponsored an oceanographic research cruise conducted aboard the NOAA Ship Malcolm Baldrige. This report presents the analytical and quality control procedures and data from the cruise that was conducted for the Ocean-Atmosphere Carbon Exchange Study (OACES). Samples were taken at 101 stations. The data presented in this report includes hydrography, nutrients, total dissolved inorganic carbon dioxide (DIC), fugacity of carbon dioxide (fCO₂), total alkalinity (TA), pH, total organic carbon and nitrogen data (TOC/TON), chlorofluorocarbons, ¹³C, and biological parameters.

Abstract:

The increase of total dissolved inorganic carbon (DIC) in the ocean caused by the uptake of fossil fuel CO₂ is estimated mostly by ocean models. These model estimates need to be verified using field measurements. However, the direct detection of the anthropogenic CO₂ signal in the ocean has been hampered by the relatively small annual increase in DIC in seawater (~1 µmol/kg/yr, as compared with background DIC of ~2000 µmol/kg) and by lack of high-precision measurements in the past. With the recent improvement in DIC analyses techniques, it has now become possible to detect the anthropogenic CO₂ signal on decadal time scales. Here we report a significant increase in DIC between the GEOSECS survey in 1978 and the recent NOAA-OACES survey in 1995 in the Indian Ocean. The anthropogenic CO₂ signal is 12 ± 4.5 µmol/kg at ~300 m (potential density, σ_θ = 26.6) and the signal decreases on denser isopycnal horizons down to undetectable near ~1000 m (σ_θ = 27.2). The data are used to illustrate the isopycnal analysis and corrections necessary to determine the anthropogenic CO₂ increase over time. The work can be used as a guide for future observational strategies to assess uptake of anthropogenic CO₂.

Abstract:

Subsurface fugacities of CO₂ (fCO₂(20)) can be used in combination with total dissolved inorganic carbon (DIC) to precisely calculate total alkalinity. Thus, it can be used to determine dissolution of calcium carbonate (hard tissue) and remineralization of organic material (soft tissue), to quantify saturation constants of calcite and aragonite in seawater, and to characterize water masses. fCO₂(20) is a good tracer of biological transformation since it is thermodynamically related to the other inorganic carbon system parameters and it has a dynamic range from 200 to 2000 µatm in the world's ocean. Precision of fCO₂ measurements is better than 0.3% and the values are well calibrated using compressed gas reference standards. Increases of fCO₂(20) are observed as the water masses age during movement from the Atlantic to the Indian and South Pacific Oceans. As an example of the determination of the ratio of soft tissue remineralization to hard tissue dissolution from fCO₂(20) and DIC, the trends along the 27.2 isopyncal for the subtropical gyres of the three basins are investigated. Little CaCO₃ dissolves along this isopycnal in the Atlantic and the South Pacific while the soft tissue remineralization to hard tissue dissolution ratio in the Indian Ocean is 4.5:1. The difference in this ratio along the 27.2 isopycnal appears to be a combination of the calcite and aragonite saturation levels and the supply of aragonite tests.

Abstract:

As part of the U.S. JGOFS Program and the NOAA Ocean-Atmosphere Carbon Exchange Study (OACES), measurements of CO₂ partial pressure were made in the atmosphere and in the surface waters of the central and eastern equatorial Pacific during the boreal spring and autumn of 1992, the spring of 1993, and the spring and autumn of 1994. Surface-water pCO₂ data indicate significant diurnal, seasonal, and interannual variations. The largest variations were associated with the 1991-1994 ENSO event, which reached maximum intensity in the spring of 1992. The lower values of surface-water DELTApCO₂ observed during the 1991-1994 ENSO period were the result of the combined effects of both remotely and locally forced physical processes. The warm pool, which reached a maximum eastward extent in January-February of 1992, began in September of 1991 as a series of westerly wind events lasting about 30 days. Each wind event initiated an eastward-propagating Kelvin wave which caused a deepening of the thermocline. By the end of January 1992 the thermocline was at its maximum depth, so that the upwelled water was warm and CO₂-depleted. In April of the same year, the local winds were weaker than normal, and the upwelling was from shallow depths. These changes resulted in a lower-than-normal CO₂ flux to the atmosphere. The results show that for the one-year period from the fall of 1991 until the fall of 1992, approximately 0.3 GtC were released to the atmosphere; 0.6 GtC were released in 1993, and 0.7 GtC in 1994, in good agreement with the model results of Ciais et al. (Science, 269, 1098-1102; J. Geophys. Res., 100, 5051-5070). The net reduction of the ocean-atmosphere CO₂ flux during the 1991-1994 El Niño was on the order of 0.8-1.2 GtC. Thus, the total amount of CO₂ sequestered in the equatorial oceans during the prolonged 1991-1994 El Niño period was about 25% higher than the severe El Niño of 1982-1983.

Abstract:

The relationship between gas transfer velocity and rain rate was investigated at NASA's Rain- Sea Interaction Facility (RSIF) using several SF₆ evasion experiments. During each experiment, a water tank below the rain simulator was supersaturated with SF₆, a synthetic gas, and the gas transfer velocities were calculated from the measured decrease in SF₆ concentration with time. The results from experiments with 18 different rain rates (7 to 110 mm h^-1) and 1 of 2 dropsizes (2.8 or 4.2 mm diameter) confirm a significant and systematic enhancement of air-water gas exchange by rainfall. The gas transfer velocities derived from our experiment were related to the kinetic energy flux calculated from the rain rate and dropsize. The relationship obtained for mono-dropsize rain at the RSIF was extrapolated to natural rain using the kinetic energy flux of natural rain calculated from the Marshall-Palmer raindrop size distribution. Results of laboratory experiments at RSIF were compared to field observations made during a tropical rainstorm in Miami, Florida and show good agreement between laboratory and field data.

Abstract:

From February through September 1994, underway measurements of the fugacity (partial pressure) of carbon dioxide (fCO₂) were performed in the eastern equatorial Pacific as part of the Ocean Atmosphere Carbon Exchange Study (OACES) of the National Oceanic and Atmospheric Administration (NOAA). The measurements were performed with semi-autonomous instruments which measured the fugacity in the air and in the headspace of an equilibrator drawing water from the bow of the ship, from which the fCO₂ of the surface water is calculated. From the difference in fugacity in air and water, the CO₂ flux from the equatorial Pacific can be estimated. On the NOAA Ship Malcolm Baldrige the system measured three reference standards, three air values, and eight water values per hour. The system on the Discoverer measured three standards, one 19-minute average air sample, and one 20-minute average water sample per hour. This report contains a description of the methodology and reduction of the fCO₂ and ancillary measurements. The results from the cruises of the Malcolm Baldrige in the equatorial Pacific in the (boreal) spring and fall of 1994 and from the Discoverer along nominally 110°W in the spring of 1994 are shown in a series of graphs with fCO₂ air and water versus latitude as top panel and temperature and salinity versus latitude as bottom panel.

Abstract:

NOAA's Climate and Global Change (CGC) Program sponsored a major cooperative effort in the eastern Pacific along WOCE Hydrographic Programme Line P18 from 26 January to 27 April 1994. The first leg (Leg 1) consisted of a transit from Seattle to Punta Arenas, Chile. The second leg (Leg 2) covered hydrographic stations from 67°S, 103°W to 27°S, 103°. The third leg (Leg 3) included stations between 26.5°S, 103°W and 23°N, 110°W. Full depth CTD/rosette casts were made to the ocean bottom at a nominal spacing of 30 miles on Legs 2 and 3. Water samples were collected on the casts for analyses of concentrations of salinity, DO, CFC, fCO₂, DIC, TAlk, pH, TOC/TON, ¹³C/¹²C isotopes, and nutrients. Biological parameters were also sampled, and included biogenic Si, chlorophyll-a, phaeopigments, and primary productivity.

Abstract:

During the National Oceanic and Atmospheric Administration's Ocean Atmosphere Carbon Exchange Study expedition in the eastern North Atlantic in summer 1993, measurements of four CO₂ parameters, along with hydrographic properties, were made: fugacity of CO₂, fCO₂ (measured at 20°C and in situ); pH (measured at 20°C); total inorganic carbon, TCO₂; and total alkalinity, TA. The major objective of this cruise was to establish a benchmark against which future measurements of the transient invasion of CO₂ can be made. The large-scale distributions of surface water CO₂ parameters were related to temperature and salinity in this region. The subsurface TA and TCO₂ measurements were fitted to multiple linear functions of salinity, in situ temperature, apparent oxygen utilization, and silicate. The measurements of the inorganic carbon system were also used to examine the internal consistency of the carbonate system in this area. The measurements were internally consistent to ±1.3% in fCO₂, ±0.006 in pH, ±3 µmol kg^{- 1} in TCO₂, and ±3 µmol kg^-1 in TA if proper carbonic acid dissociation constants are used for different input combinations. The thermodynamic constants of Goyet and Poisson (1989), Roy et al. (1993), Millero (1995), and Lee and Millero (1995) were most consistent with the measurements of pH (at 20°C), TCO₂, and TA. However, if fCO₂ (at 20°C) is used in thermodynamic calculations, the constants of Mehrbach et al. (1973) gave the best representation of measurements. The constants of Lee and Millero (1995) were also in reasonable agreement with these measurements.

Abstract:

From February 1995 through January 1996 the NOAA ship Malcolm Baldrige conducted scientific operations on an around-the-world tour. The majority of work occurred in the Indian Ocean. The CO₂ groups of the National Oceanic and Atmospheric Administration's (NOAA) Atlantic Oceanographic and Meteorological Laboratory (AOML) and Pacific Marine Environmental Laboratory (PMEL) operated a continuously flowing partial pressure carbon dioxide analyzer. Samples were taken from both the surface water and the overlying atmosphere to determine carbon dioxide flux across the gas/water interface. Other parameters such as salinity, barometric pressure, and temperature were used to reduce the data and calculate the fugacity of CO₂*. Total dissolved inorganic carbon (DIC) samples of surface water were also collected. Data were collected on each leg of the cruise. Leg 1 was a transit from Miami to Durban, South Africa. Leg 2 operated from Durban to Colombo, Sri Lanka. Leg 3 operated from Colombo to Muscat, Oman. Leg 4 operated from Muscat to Victoria, Seychelles. Leg 5 operated from Victoria to Muscat, Oman. Leg 6 operated from Muscat to Diego Garcia. Leg 7 consisted of a transit from Diego Garcia to Fremantle, Australia followed by the major scientific operations between Fremantle and Male, Maldive Islands. Leg 8 included another transit from Male to Darwin, Australia. Operations began after leaving Darwin and headed into the western equatorial Pacific. The ship inported in American Samoa and continued to Panama, Miami, Florida and finished in Charleston, South Carolina. Descriptions of sampling methods and graphical data summaries are given in this report.

Abstract:

No abstract.

Abstract:

Approximately 250,000 measurements made for the pCO₂ difference between surface water and the marine atmosphere, ΔpCO₂, have been assembled for the global oceans. Observations made in the equatorial Pacific during El Niño events have been excluded from the data set. These observations are mapped on the global 4° × 5° grid for a single virtual calendar year (chosen arbitrarily to be 1990) representing a non-El Niño year. Monthly global distributions of ΔpCO₂ have been constructed using an interpolation method based on a lateral advection-diffusion transport equation. The net flux of CO₂ across the sea surface has been computed using ΔpCO₂ distributions and CO₂ gas transfer coefficients across sea surface. The annual net uptake flux of CO₂ by the global oceans thus estimated ranges from 0.60 to 1.34 Gt-C • yr^-1 depending on different formulations used for wind speed dependence on the gas transfer coefficient. These estimates are subject to an error of up to 75% resulting from the numerical interpolation method used to estimate the distribution of ΔpCO₂ over the global oceans. Temperate and polar oceans of both hemispheres are the major sinks for atmospheric CO₂, whereas the equatorial oceans are the major sources for CO₂. The Atlantic Ocean is the most important CO₂ sink, providing about 60% of the global ocean uptake, while the Pacific Ocean is neutral because of its equatorial source flux being balanced by the sink flux of the temperate oceans. The Indian and Southern Oceans take up about 20% each.

Abstract:

A Lagrangian tracer study was performed on the West Florida Shelf in April 1996 using deliberately injected trace gases. Although such studies have been performed previously, this work is the first where the deliberate tracers, in conjunction with carbon system parameters, are used to quantify changes in water column carbon inventories due to air-sea exchange and net community metabolism. The horizontal dispersion and the gas transfer velocity were determined over a period of 2 weeks from the change in both the concentrations and the concentration ratio of the two injected trace gases, sulfur hexafluoride (SF₆) and helium-3 (³He). Horizontal diffusion estimates were about an order of magnitude greater than calculated from empirical equations, and the difference is attributed to vertical shear. The second moment of the patch grew to 1.6 × 10³ km² over a period of 11 days. The gas transfer velocity, normalized to CO₂ exchange at 20°C, was 8.4 cm hr^-1 at an average wind speed, U₁₀, of 4.4 m s^-1 for the duration of the experiment, which is in good agreement with empirical estimates. Remineralization rates exceeded productivity, causing an increase in dissolved inorganic carbon of about 1 µmol kg^-1 day^-1 in the water column. During this period of senescence, 80% of the increase in inorganic carbon is attributed to community remineralization and 20% due to invasion of atmospheric CO₂. This net remineralization is in accordance with in situ and on-deck incubation experiments.

Abstract:

The dual-gaseous tracer technique is a new and reliable method for directly measuring air-sea gas transfer velocities. However, analysis of data from these experiments requires the assumption that the dependence of the transfer velocity on molecular diffusivity is constant. Modeling and laboratory studies indicate that this could be an invalid assumption when gas transfer through bubbles generated by breaking waves is a significant portion of the sea-to-air gas flux. Here, a parameterization of the transfer velocity in terms of wind speed and fractional area whitecap coverage is developed that includes the effects of bubble-mediated exchange processes. It is shown that transfer velocities estimated using this parameterization are consistent with available oceanic gas exchange measurements. The parameterization is then used to investigate the consequences of including whitecap-related transfer processes in the analyses of data derived from dual-tracer experiments. In the case of the tracer pair, sulfur hexafluoride and helium-3, it is shown that assuming a constant diffusivity dependence underestimates transfer velocities of helium-3 by up to 20% at high wind speeds. It is also shown that using the parameterization to normalize the transfer velocity for helium-3 to carbon dioxide results in a 6% decrease in the estimated transfer velocity compared to constant-diffusivity dependence estimates.

Abstract:

Toward a method for estimating air-sea gas transfer velocities, k_L, from remote measurements of fractional area whitecap coverage, W_C, a gas exchange experiment was conducted in an outdoor surf pool during the October 1993 Wave Basin Experiment (WABEX-93). For both spilling and plunging breaking waves, measurements were made of W_C; air-water fluxes of carbon dioxide, helium, nitrous oxide, oxygen, and sulfur hexafluoride; microwave brightness temperature of the water surface, sigma; aqueous-phase turbulence velocities; and bubble size spectra. The data show that k_L, scales as a common, linear relation with W_C for both spilling and plungin breaking waves. The gas transfer data have been used to develop an empirical parameterization for predicting k_L from W_C, Schmidt number, and solubility.

Abstract:

Gas transfer velocities were determined using the dual tracer technique (³He and SF₆) for two 40-60 km reaches of the tidal Hudson River. The experiments were performed near Poughkeepsie, New York in 1993 and near Catskill, New York in 1994. During both experiments wind speeds were measured above the river. The shape of daily axial SF₆ distributions and the evolution of peak concentrations followed patterns predicted by the one-dimensional advection-diffusion equation. Mean gas transfer velocities calculated from the 1994 data using the temporal change in SF₆ inventory (4.6 ± 0.4 cm hr^-1) and the tracer ration (5.3 ± 0.2 cm hr^-1) are in good agreement, suggesting that the dual tracer technique yields reasonable results. The relationships between gas transfer velocity and wind speeds found during these experiments are very similar to those observed previously for lakes, suggesting that wind is the primary source of surface turbulence in these reaches of the tidal Hudson River. The results of the 1993 and 1994 experiments agree very well, indicating that the local geometry of the river is of secondary importance.

Abstract:

Bubble-mediated gas transfer velocities were determined in a freshwater surf pool during WABEX-93. Gas transfer of N₂O, He, and SF₆ were measured under eight different mechanically-generated, breaking-wave conditions. Contrary to gas transfer across an air-water interface, where the transfer is solely a function of surface turbulence and the molecular diffusion coefficient of the gas, exchange through bubbles is also a function of the solubility of the gas, bubble size, and bubble penetration depths. The relative rates of gas transfer through bubbles of N₂O, CO₂, He, and SF₆ for the experiment are compared with models developed by Woolf (1995) and Keeling (1992). The model of Woolf shows reasonable agreement with the observed results while that of Keeling overpredicts the exchange of N₂O. The trend suggests that in the surf pool experiments the solubility dependence of the model of Keeling is too strong while that of Woolf is slightly too weak compared to the observations.

Abstract:

Exchange of carbon dioxide (CO₂) under low turbulence conditions and high pH can be enhanced by hydration reactions of CO₂ with hydroxide ions and water molecules in the boundary layer.  A series of field experiments was performed on several lakes, including alkaline closed-basin lakes, using enclosures (helmets) to study the enhancement process in nature.  In addition, the enhancement of CO₂ exchange was studied in laboratory experiments using freshwater and seawater.  The results of the experiments are compared with published theoretical calculations. Within the experimental uncertainties and shortcomings of the chemical enhancement models, reasonable agreement was observed between experimental and theoretical results for seawater.  The experiments indicate, in accordance with theory, that chemical enhancement has a minor effect on air-sea gas exchange of CO₂ under average oceanic turbulence conditions.  However, for the equatorial CO₂ source regions, with high temperatures and low winds, the calculated CO₂ enhancement amounts to 4% to 8% of the total exchange. The observations on lakes show poorer agreement with models which is attributed to experimental uncertainty and poor characterization of the chemistry of the lake waters.  The experiments show that chemical enhancement of CO₂ is ubiquitous for the alkaline close basin lakes with enhancements of up to a factor of three.

Abstract:

The fugacity of CO₂ in surface water (fCO_2W) was measured in the eastern equatorial Pacific (EEP) during the boreal spring and fall of 1992 and in the spring of 1993. A prolonged El Niño occurred during this period with anomalously warm sea surface temperatures (SST) during the spring of 1992 and 1993. Correspondingly, the fCO_2W values were lower than historical non-El Niño values at the equator. However, the fCO_2W in the spring of 1993 was up to 50 µatm higher than in the spring of 1992, despite similar SSTs. The trend is attributed to the slower response times of factors causing fCO_2W decrease compared to rapid increase of fCO_2W by upwelling cold water with high carbon content and subsequent heating. During the fall of 1992, SSTs south of the equator were 5°C cooler than in the spring, which is indicative of vigorous upwelling of water with high CO₂ content from below the thermocline. Decreases in fCO_2W due to net biological productivity and gas exchange take of the order of months, causing the fCO_2W levels during the spring of 1993 to be elevated compared to the spring of the previous year. Our data and data obtained in 1986 and 1989 along 110°W suggest that fCO_2W maxima in the equatorial Pacific can be either associated with temperature minima or temperature maxima. Despite the multitude of factors which influence fCO_2W, most of the variance can be accounted for with changes in nitrate and SST. A multilinear regression of fCO_2W with SST and nitrate for the 1992 data has a standard error in predicted fCO_2W of 10 µatm. Air-sea fluxes of CO₂ in the EEP were estimated to be 30% higher in the spring of 1993 and 10% higher in the fall of 1992 than in the spring of 1992.

Abstract:

An analysis system is described to measure the fugacity of CO₂ (fCO₂)¹ in 500 mL of seawater (discrete samples) by infrared analysis. The unit has been used on oceanographic research cruises sponsored by the Ocean-Atmosphere Carbon Exchange Study (OACES) of NOAA since 1991 for a total of approximately 10,000 measurements. The precision of the analyses based on replicate samples during routine analysis is 0.2%. Precision is primarily limited by sample storage, and the difference between headspace gas and water CO₂ concentrations prior to equilibration. The precision and accuracy of the instrument is estimated in several different ways. A preliminary side by side test of two different discrete fCO₂ systems using an infrared (IR) analyzer and a gas chromatograph (GC) shows a variability of 0.8% without significant bias. For surface waters the discrete measurements are compared with measurements from a continuous flowing underway system which was deployed on all cruises. Select comparisons with fCO₂ calculated from spectrophotometric pH and DIC (Total Dissolved Inorganic Carbon) measurements are performed. These comparisons are limited by uncertainty in the magnitude and the temperature dependence of the carbon and borate dissociation constants. Indirect comparisons are made with pCO₂ measurements of Drs. Takahashi and Chipman of LDEO in the South Atlantic and equatorial Pacific (EqPac). Although the measurements were performed months (for the EqPac study in 1992) to years (for the South Atlantic study in 1989 and 1991) apart, some inferences can be made by normalizing the fCO₂ values and by performing the comparison in property space. The comparison indicates that the precision of our system is comparable to that of the LDEO system. The surface values obtained from the LDEO system during EqPac are 1.5 to 3% lower. There is inconclusive evidence that some of the subsurface LDEO pCO₂ values are lower as well. However, the comparison of subsurface values for the North Atlantic Deep Water in the South Atlantic study shows good agreement. Because of the current uncertainty in dissociation constants, there is no a priori way to determine which value is correct.

Abstract:

Gas transfer velocities for two gases, SF₆ (sulfur hexafluoride) and ³He, were determined in a small pond by injecting a mixture of these gases into the water and monitoring the decline of their concentrations over the next eight days. For wind speeds between 1.5-2.5 m s^-1, no variations of gas transfer velocity with wind speed could be resolved with our data. Gas transfer velocities at wind speeds greater than 3 m s^-1 were substantially larger and consistent with other lake tracer experiments. From the ratio of gas transfer velocities for SF₆ and ³He, we calculated the Schmidt number exponent to be 0.57 ± 0.07.

Abstract:

As part of the U.S. JGOFS Equatorial Pacific Process Study, measurements of fCO₂ were determined for the atmosphere and in the surface waters of the central and eastern equatorial Pacific during the spring and autumn of 1992 and 1993, and the spring of 1994 after the 1992-1993 ENSO event. Surface water fCO₂ data indicate significant differences between the springtime El Niño conditions and the autumn post-El Niño conditions. The autumn fugacity (ΔfCO₂) maxima were approximately 15-55 µatm higher than in the spring. The lower surface ΔfCO₂ values in the spring data set were the result of: (1) advection of CO₂-depleted water from the west at the equator near 170°W; and (2) reduced upwelling and lower ΔfCO₂ distributions as consequence of lighter zonal winds in the eastern Pacific from 140°W to 110°W. In the spring of 1993 elevated sea surface temperatures were observed in spring of 1992. In spring 1994 sea surface temperatures were near the climatological mean and fCO₂ levels were 70-90 µatm higher than the 1992 levels. These results clearly indicate that the largest sustained fCO₂ variations in the eastern equatorial Pacific occur during ENSO events.

Abstract:

As part of the U.S. JGOFS Equatorial Pacific Process Study, measurements of CO₂ species concentrations were made in the atmosphere and in the surface waters of the central and eastern equatorial Pacific during the boreal spring and autumn of 1992. Surface water fCO₂ data indicate significant differences between the springtime El Niño conditions and the autumn post-El Niño conditions. The autumn fugacity (ΔfCO₂) maxima were approximately 15-55 µatm higher than in the spring. The lower surface DELTA fCO₂ values in the spring data set were the result of: (1) advection of CO₂-depleted water from the west at the equator near 170°W; and (2) reduced upwelling and lower ΔfCO₂ distributions as a consequence of lighter zonal winds in the eastern Pacific from 140°W to 110°W. Assuming the springtime data are representative of the El Niño conditions and the autumn data are representative of the post-El Niño conditions, it is estimated that the net annual CO₂ flux during the 1991-1992 ENSO period is 0.3 Gt C. Over 60% of this flux occurred during the four-month period in the autumn when ΔfCO₂ values were close to normal. The net annual reduction of the ocean-atmosphere CO₂ flux during the 1991-1992 El Niño is estimated to be on the order of 0.5-0.7 Gt C.

Abstract:

No abstract.

Abstract:

In the boreal autumn of 1992, NOAA's Climate and Global Change Program sponsored a major cooperative effort with the U.S. JGOFS Program in the central and eastern equatorial Pacific to investigate the unique role of equatorial processes on CO₂ cycling during and following the 1991-1992 ENSO event. Data were collected meridionally along four transects, generally between 10°N and 10°S. The first leg (Leg 3) included the 140°W and 125°W transects; the second leg (Leg 4) sampled along 110°W, and the third leg (Leg 5) included stations along 95°W and three short transects extending westward from the Peru coast. Chemical parameters sampled included fCO₂, DIC, TAlk, pH, TOC, and nutrients. Ancillary measurements of salinity, temperature, and dissolved oxygen (DO) were also taken. Descriptions of sampling methods and data summaries are given in this report.

Abstract:

From February 24 to May 19, 1992, the National Oceanic and Atmospheric Administration's (NOAA) Climate and Global Change Program sponsored a major cooperative effort with the U.S. Joint Global Ocean Flux Study (U.S. JGOFS) to study the role of equatorial processes on CO₂ cycling in the central and eastern equatorial Pacific during the 1991-1992 El Niño Southern Oscillation (ENSO) event. The NOAA Ship Malcolm Baldrige performed four transequatorial sections in the region, and this report presents hydrographic and chemical data from that cruise, including tables of the following data from each station: hydrography from each CTD cast at the bottle trip depths, dissolved oxygen, fCO₂, DIC, pH, TAlk, nutrients, and TOC. Descriptions of the sampling techniques and analytical methods used in the collection and processing of these data are also presented.

Abstract:

No abstract.

Abstract:

During the (boreal) spring and fall of 1992, the NOAA Ocean-Atmosphere Carbon Exchange Study did an intensive survey of upper water column (2 values were significantly lower in the spring, while sea surface temperatures south of the equator were higher. The seasonal change in surface water chemistry at the equator is due to changes in upwelling of nutrient and carbon-enriched water. Oxygen and CO₂ anomalies at the surface point to approximately a three-fold increase in upwelling of thermocline water in the fall compared to the spring. The large-scale spatial variations in the surface chemistry patterns remained unchanged between spring and fall. There was a westward decrease in surface-water carbon and nitrate concentrations and a strong north to south asymmetry with higher carbon and nitrate values south of the equator. This pattern is attributed to input of carbon and nutrients with the South Equatorial Current from the east. Using velocities obtained from surface drifter tracks, along with reasonable gas exchange estimates and a "Redfield analysis" to account for export biological production, this westward decrease in carbon and nutrients can be quantitatively accounted for in the region from 0°to 3°S and 110°W to 140°W in the spring. In the fall the calculated concentration decrease is greater than observed, which is attributed to input from local equatorial upwelling along the pathway of water transit.

Abstract:

Gas exchange rates have been determined in the tidal Hudson River by injecting two inert gases, ³He and sulfur hexafluoride (SF₆), and monitoring their decline with time. Their distributions along the main axis of the river were approximately Gaussian and maximum concentrations of excess ³He and SF₆ observed during each transect decreased from about 6500 × 10^-16 cm³ STP g^-1 and 250 ppt (part per trillion by volume), respectively, to values close to atmospheric equilibrium concentration were observed. After three days of mixing, tracer concentrations in bottom samples were 0-19% greater than in surface samples. Gas transfer velocities were calculated from the temporal change in the depth-averaged excess ³He/SF₆ ratio from stations having maximum tracer concentrations. They ranged from 1.5 to 9.0 cm h^-1 and correlated well with mean wind speed.

Abstract:

Tropical instability waves have been shown to have a major impact on the variability of temperature and nutrients along the equatorial wave guide. In order to assess the impact of these features on carbon species distributions during an ENSO event, sea surface temperature, salinity, sigma-t, nitrate, CO₂ fugacity, total inorganic carbon, total alkalinity, and pH along the equator were measured from 130°W to 100°W during 8-15 May 1992. Concurrent moored measurements of surface currents and temperature were also made at 0°, 110°W. Results indicate that tropical instability waves, with periods of 15-20 days and zonal wavelengths of 700-800 km, controlled the observed spatial variability of the CO₂ species, nitrate, and hydrographic parameters at the equator.

Abstract:

From July 11 to September 2, 1991, the National Oceanic and Atmospheric Administration's (NOAA) Carbon Dioxide (CO₂) and Radiatively Important Trace Species (RITS) programs participated in an oceanographic research cruise conducted aboard the NOAA ship Malcolm Baldrige. This report presents the research from that cruise that was conducted for the CO₂ program, which has recently been renamed the Ocean-Atmosphere Carbon Exchange Study (OACES). During leg 1 of this cruise (Fortaleza, Brazil to Montevideo, Uruguay), 33 CTD hydrographic casts and 17 Go-Flo™ hydrographic (productivity) casts were conducted. Samples were also collected while underway on leg 1, for the determination of the fugacity of CO₂ (fCO₂) of the air and surface water. Leg 2 (Montevideo, Uruguay to Fortaleza, Brazil) collected 21 days of underway fCO₂ measurements, conducted five CTD hydrographic casts, and nine Go-Flo™ hydrographic (productivity) casts. This report contains tables of the following data: hydrography from each CTD cast at the bottle trip depths (including salinity, oxygen and nutrients), discrete carbon parameters, underway carbon parameter values, and data from productivity casts. Descriptions of the sampling techniques and analytical methods used in the collection and processing of these data are also presented in this report.

Abstract:

It has long been hypothesized that iron concentrations limit phytoplankton productivity in some parts of the ocean. As a result, iron may have played a role in modulating atmospheric CO₂ levels between glacial and interglacial times, and it has been proposed that large-scale deposition of iron in the ocean might be an effective way to combat the rise of anthropogenic CO₂ in the atmosphere. As part of an experiment in the equatorial Pacific Ocean, we observed the effect on dissolved CO₂ of enriching a small (8 × 8 km) patch of water with iron. We saw significant depression of surface fugacities of CO₂ within 48 hours of the iron release, which did not change systematically after that time. But the effect was only a small fraction (similar to 10%) of the CO₂ drawdown that would have occurred had the enrichment resulted in the complete utilization of all the available nitrate and phosphate. Thus artificial fertilization of this ocean region did not cause a very large change in the surface CO₂ concentration, in contrast to the effect observed in incubation experiments, where addition of similar concentrations of iron usually results in complete depletion of nutrients. Although our experiment does not necessarily mimic all circumstances under which iron deposition might occur naturally, our results do not support the idea that iron fertilization would significantly affect atmospheric CO₂ concentrations.

Abstract:

Measurements from scatterometers pointing at wind-waves in three large wave-tanks are examined to study fetch effects and the correlation with wind friction-velocity u_*. Time-series measurements were made at 13, 35, and 95 m with a K_a-band scatterometer aimed upwind at 30° incidence angle and vertical polarization. Average normalized radar cross-section sigma_o values from all fetches follow a common trend for sigma_o as a function of u_*, so the fetch dependence is negligible. An empirical power-law model yields a high correlation between sigma_o and u_*, but because systematic anomalies arise, we re-examine a turbulence approach that delineates low and high regimes with a transition at u_* of approximately 25 cm s^-1. Using this criteria, the data are well represented by a two-section power-law relationship between sigma_o and u_*.

Abstract:

During a recent NOAA JGOFS equatorial Pacific cruise, all four analytical parameters of the carbonate system were measured: pH, total alkalinity (TA), total carbon dioxide (TCO₂), and the fugacity of carbon dioxide (fCO₂). The measurements made during leg 2 on surface waters have been used to examine the internal consistency of the carbon dioxide system in these waters. The internal consistency of the measurements was examined by using various inputs of the measured parameters (pH-TA, pH-TCO₂, pH-fCO₂, fCO₂-TCO₂, and TA-TCO₂) to calculate the components of the CO₂ system. The results indicate that the measurements have an internal consistency of ±0.003-0.006 in pH, ±5-7 µmol kg^-1 in TCO₂, and ±6-9 µAtm in fCO₂ if reliable constants are used for the dissociation of carbonic acid in seawater. These results indicate that our present understanding of the thermodynamics of the carbonate system in seawater is close to the present accuracy in measuring the various parameters of the system (±0.0002 in pH, ±4 µmol kg^-1 in TA, ±2 µmol kg^-1 in TCO₂, and ±2 µAtm in fCO₂).

Abstract:

Instrumentation and methodology is described which is used for measurement of the fugacity (or partial pressure) of carbon dioxide (fCO₂ or pCO₂) in surface seawater. Two separate instruments were developed for the measurements. One is an underway system which measures the mixing ratio of CO₂, XCO₂, in a headspace in equilibrium with surface seawater continuously pumped into a 24 l-equilibrium chamber. The other is a discrete system in which 460 ml aliquots of water areequilibrated with a 120 ml headspace. Both systems use a non-dispersive infrared analyzer as detector. In the underway instrument the average XCO₂ in the headspace of an equilibration chamber is measured at near in-situ temperature over 20 min each hour. At a cruising speed of 13 knots this translates into a space averaged fCO₂ value over 8 km. The underway system is ideally suited for mapping of the surface water fugacity over large geographic regions. Samples from the discrete instrument are analyzed at 20°C. The primary function of the system is for measurement of CO₂ and other (carbon) parameters sub-sampled from the same aliquot. To calculate the fCO₂ in water for in-situ conditions from the mixing ratio in the headspace of the flask of the discrete system, small carbon mass balance and, sometimes significant, temperature corrections have to be applied. Comparison of 100 surface values obtained in the South Atlantic using the underway and discrete systems shows that the average difference of pCO₂ values for the two systems ranges from -4.3 µatm to -8.6 µatm, depending on the temperature correction, with a standard deviation of 4 µatm. The differences show scatter of up the 15 µatm which we attribute to a mismatch between the point samples for the discrete system and the integrated samples for the underway system.

Abstract:

A gas exchange experiment was performed on Georges Bank using the deliberate tracers sulfur hexafluoride (SF₆) and helium 3 (³He). The concentrations of the tracers were measured in the water column over a period of 10 days. During this time the patch grew from an 8-km-long injection streak to an area of about 500 km². The gas transfer velocity was determined from the change in the ratio of the tracers over time scaled to the ratio of their Schmidt numbers. A near-linear relationship between gas exchange and wind speed was observed based on four experimental points covering a wind speed range from 3 to 11 m/s. The results fall in the upper part of the range of gas transfer-wind speed relationships developed to date. Wind speeds during the experiment obtained from anemometers on the ship, on a free floating drifter, and on a fixed mooring showed significant differences. With the ability to measure gas transfer velocities over the ocean on time scales of several days, accurate wind speed/stress measurements are imperative to obtain a robust relationship between gas transfer and wind speed.

Abstract:

Laboratory results have demonstrated that bubble plumes are a very efficient air/water gas transport mechanism. Because breaking waves generate bubble plumes, it may be possible to correlate air/sea gas transport velocities with whitecap coverage. This correlation may then allow transport velocities to be predicted from measurements of apparent microwave brightness temperature through the increase in sea surface microwave emissivity associated with breaking waves. In order to develop this remote-sensing based method for predicting air/sea gas fluxes, the whitecap simulation tank at Battelle/Marine Sciences Laboratory was used to measure transport velocities for oxygen, helium, sulfur hexafluoride, and dimethyl sulfide. This allowed the gas exchange process to be studied as a function of fractional areabubble plume coverage, molecular diffusivity (or Schmidt number), and water temperature. Using these results, an empirical model has been developed that permits prediction of the transport velocity in the Whitecap Simulation Tank from bubble plume coverage and Schmidt number. The implications of these results to the analysis of in situ dual-tracer air/sea gas transport dataare also discussed.

Abstract:

EqPac is the United States-Joint Global Ocean Flux Study (US-JGOFS) process study in the central equatorial Pacific. The first EqPac cruises sailed in January 1992 during a moderately strong El Niño. This was fortuitous for our studies of chemical and biological distributions because El Niño events are difficult to predict, and the lead time for a project of this size is long. There was virtually no previous upper-water-column chemical or biological data for El Niño conditions in the central equatorial Pacific. Now an El Niño has been studied in considerable detail, and it will be easy to sample the extremes in environmental conditions by sampling non-El Niño conditions (including La Niña) in 1993 and the years thereafter. The implementation of EqPac illustrates how difficult it is to mount a large-scale interdisciplinary study of the ocean when the interannual variability is large.

Abstract:

Relationships between wind speed and gas transfer, combined with knowledge of the partial pressure difference of CO₂ across the air-sea interface are frequently used to determine the CO₂ flux between the ocean and the atmosphere. Little attention has been paid to the influence of variability in wind speed on the calculated gas transfer velocities and the possibility of chemical enhancement of CO₂ exchange at low wind speeds over the ocean. The effect of these parameters is illustrated using a quadratic dependence of gas exchange on wind speed which is fit through gas transfer velocities over the ocean determined by the natural-¹⁴C disequilibrium and the bomb-¹⁴C inventory methods. Some of the variability between different data sets can be accounted for by the suggested mechanisms, but much of the variation appears due to other causes. Possible causes for the large difference between two frequently-used relationships between gas transfer and wind speed are discussed. To determine fluxes of gases other than CO₂ across the air-water interface, the relevant expressions for gas transfer, and the temperature and salinity dependence of the Schmidt number and solubility of several gases of environmental interest, are included in an appendix.

Abstract:

Radiocarbon measurements suggest that ¹⁴C-free carbon enters from beneath Mono Lake at a rate of about 1 mol/m²/yr. An input of this magnitude should be manifested in the inorganic carbon budget of the lake and, with this in mind, we have devised a model to reconstruct the evolution of the partial pressure of CO₂ (pCO₂) over the past 150 years. This encompasses a period (1945 to present) during which major diversions of source water via the Los Angeles aqueduct have been in effect, significantly increasing the salinity of the lake and,hence, its pCO₂. The model has been constrained by experimental characterization of the carbonate chemistry of the lake water, by the temperature dependence of pCO₂ for the lake water, and by pCO₂ measurements made on the lake water in 1966, 1969, 1981, and 1989. Our calculations suggest that prior to 1945 the pCO₂ of about 3.3 mol/m²/yr is required. Volcanic activity beneath the lake is a probable source of this input.

Abstract:

Gas transfer velocities across the air-water interface are correlated with wind speed, friction velocity, and radar backscatter from the surface in a large wind-wave tank in Delft, The Netherlands. The rates of sulfur hexafluoride and nitrous oxide exchange were measured at wind speeds ranging from 3.5 m/s to 20 m/s, and with mechanically generated waves in the 100 m long, 8 m wide, and 0.7 m deep tank. Gas transfer velocities were related to wind speed with a power law dependence. Gas transfer showed a linear dependence with friction velocity. An exponential relationship between gas transfer and average radar backscatter cross section fits the wind tunnel data well for microwave units operating at 13.5 and 35 GHz in VV and HH polarization. The relative rates of gas exchange of the two gases confirm an inverse square root dependence on the Schmidt number at intermediate wind speeds. A slight enhancement of sulfur hexafluoride exchange compared to nitrous oxide exchange was evident when breaking waves were present.

Abstract:

Analysis procedures and instrumentation to measure low levels of sulfur hexafluoride in seawater are described. The minimum detectable level for a 500 mL sample is about 3 x10^-17 mol/L. Concentrations from 1.5 to 300 x 10^-15 mol/L can be measured with approximately 2% precision. The procedure includes a concentration step employing a trap of Porapak-Q^c in a dry ice/2-propanol bath. The system has been used for tracer experiments in Santa Monica Basin and Santa Cruz Basin, and will be improved for future tracer release experiments in the deep ocean.