R/V Gordon Gunter Underway pCO2 Data
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Who We Are
| Rik Wanninkhof, Ph.D.
Senior Technical Scientist
| Denis Pierrot, Ph.D.
Oceanographer
About the Gordon Gunter
The NOAA Ship Gordon Gunter, commissioned on August 28, 1998 was originally the U.S. Naval Ship RELENTLESS. Beginning in March 1998, the ship was refitted to contain modern navigational electronics, oceanographic winches, sensors, sampling equipment, and a custom-designed marine mammal observation and survey station. With a home port of Pascagoula, Mississippi, the Gordon Gunter operates primarily in the Gulf of America, Atlantic and Caribbean waters. For more information on the Gordon Gunter, follow the link to its homepage.
In March, 2008, the Ocean Carbon Cycle (OCC) group at NOAA’s Atlantic Oceanographic and Meteorological Laboratory (AOML) installed an underway system to measure surface pCO2 in the Hydro Chem Lab aboard the Gordon Gunter. In August 2010, the underway system was replaced with a newer version system that could be connected more easily to the ship and other sensors. The installations were greatly facilitated by the cooperation of the ship’s officers and crew, especially the operation officers and electronic technicians. While the ship conducts the research that is the focus of a cruise, the pCO2 instrument takes 5 air and 60 water measurements every 3 hours. Data files are sent to AOML via email every day so that the system operation can be monitored. The final data are processed after a cruise is completed and then posted to international databases and to this web site.
About the Website
This web site provides access to the fugacity of CO2 (fCO2) data collected on this ship. Note, fCO2 is the partial pressure pCO2 corrected for non-ideality of the CO2 gas; they are numerically similar (fCO2 ≃ 0.995 pCO2). The processed data are organized by year and by cruise. For each cruise, the color coded fCO2 values are plotted along the ship’s cruise track on a chart. Next to each chart are links to the comma-delimited data file and the associated Readme file. To download a data file, select the year from the drop-down list box and click. Choose a chart and cruise, right-click on the link to its data file or Readme file, and select the download option. Please consult with and acknowledge the AOML Ocean Carbon Cycle group if data is used for publication or presentation (contacts in Master Readme, or Denis.Pierrot@noaa.gov).
The Master Readme provides meta data that is applicable for all data gathered from this ship. The individual Readme files next to the charts provide meta data specific to the associated cruise. The Real-Time Display link displays plots of the raw xCO2 data as a function of time and location. These plots are suitable for monitoring but are not suitable for environmental interpretation since the Real-Time data has not been processed nor quality controlled.
Gordon Gunter Underway pCO2 Data
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- Gordon Gunter 2008 Data
Gordon Gunter 2009 Data
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Gordon Gunter Master Readme
Introduction
The information presented in this file is applicable to all the data sets collected on the R/V Gordon Gunter that are presented on this page.
Any temporary changes in this information will be noted in the readme files for the individual expeditions.
Statement for use of data:
These data are made available to the public and the scientific community in the belief that their wide dissemination will lead to greater understanding and new insights. The availability of these data does not constitute publication of the data. We rely on the ethics and integrity of the user to ensure that the AOML ocean carbon group receives fair credit for its work. Please consult with us prior to use so we can ensure that the quality and limitations of the data are accurately represented.
Platform Information:
In 2008, the Ocean Carbon Group at NOAA’s Atlantic Oceanographic and Meteorological Laboratory (AOML) installed an instrument to measure CO2 levels in surface water and air on the NOAA Ship Gordon Gunter. The Gordon Gunter primarily operates in the Gulf of America, Atlantic and Caribbean waters.
Vessel Name: Gordon Gunter
Class of Data: Surface ocean carbon dioxide concentrations
Scientists responsible for the technical quality of this pCO2 dataset:
Rik Wanninkhof and Denis Pierrot
NOAA/AOML/Ocean Chemistry and Ecosystems Division
4301 Rickenbacker Causeway
Miami, FL 33149
Rik.Wanninkhof@noaa.gov
Denis.Pierrot@noaa.gov
Contact persons for this dataset:
Denis Pierrot
NOAA/AOML/Ocean Chemistry and Ecosystems Division
4301 Rickenbacker Causeway
Miami, FL 33149
Denis.Pierrot@noaa.gov
Component Specifications and Accuracies
The accuracies of all components, when operating optimally, are such that the calculated seawater fCO2 has an accuracy of 2 uatm or better and the calculated mole fraction of CO2 (XCO2) in air has an accuracy of 0.1 uatm.
Infrared Analyzer:
LI-COR model 6262 (2008 – May 2010)
Licor_6262_Manual.pdf
CO2 resolution: 0.01 umol/m
CO2 accuracy: ±1 ppm at 350 ppm
Internal pressure transducer accuracy: ±1.2 hPa
(manufacturer specifications: ±0.1% FS, where FS = 0-1150 hPa)
LI-COR model 7000 (August 2010 – current)
Licor_7000_Manual.pdf
CO2 resolution: 0.01 umol/m
CO2 accuracy: ±1% nominal
Internal pressure transducer accuracy: ±1.2 hPa
(manufacturer specifications: ±0.1% FS, where FS = 0-1150 hPa)
Equilibrator Pressure Transducer:
Setra model 239, differential pressure (2008 – current)
http://www.setra.com/ProductDetails/model_239.htm
Resolution: 0.01 hPa
Accuracy: ±0.052 hPa
(manufacturer specifications: ±0.14% FS, where FS = ±7.5 inches WC)
The absolute pressure of the equilibrator headspace reported in data files is the sum of the infrared analyzer pressure and the differential pressure from the pressure transducer attached to the equilibrator.
Equilibrator Temperature:
Hart model 1521 (August 2010 – current)
http://www.testequipmentdepot.com/hart/pdfs/1521_1522.pdf
Resolution: 0.001°C
Accuracy: ±0.025°C
Atmospheric Pressure:
Druck model RPT 350 (2008 – May 2010)
http://www.ge-mcs.com/en/pressure-and-level/transducerstransmitters/rtp350.html
Resolution: 0.01 hPa
Accuracy: ±0.08 hPa
(manufacturer specifications: ±0.02% FS, where FS = 400 hPa)
RMYoung model 61201 (maintained by ship) (August 2010 – present)
http://jsinstruments.com/files/Model%2061201%20Barometric%20Pressure%20Sensor.pdf
Resolution: 0.01 hPa
Accuracy: ±0.5 hPa
Sea Surface Salinity (maintained by ship):
SeaBird model SBE-21 (2008 – 2013)
http://www.seabird.com/sbe21-seacat-thermosalinograph
Temperature Accuracy: ± 0.01 °C
Salinity Accuracy: 0.05‰
Sea Surface Salinity (maintained by ship):
SeaBird model SBE-45 (2014 – present)
http://www.seabird.com/sbe45-thermosalinograph
Temperature Accuracy: ± 0.002 °C
Salinity Accuracy: 0.005‰
Sea Surface Temperature (maintained by ship):
Furuno model T2000 (2008 – May 2013)
Furuno T2000 Manual pdf
Temperature Resolution: 0.01 °C
Temperature Accuracy: ±0.02 °C
Sea Surface Temperature (maintained by ship):
SeaBird model SBE-38 (June 2013 – present)
http://www.seabird.com/pdf_documents/manuals/38_013.pdf
Temperature Resolution: 0.00025°C
Temperature Accuracy: ±0.001°C
Instrument Description and Configuration
The general principle of operation of the instrument can be found in Wanninkhof and Thoning (1993), Ho et al. (1995), Feely et al. (1998), and Pierrot et al. (2009). Seawater flows through an equilibrator chamber where CO2 exchanges between water and the air above it. Small changes in seawater CO2 concentration are rapidly translated into changes in CO2 concentration in the air of the chamber (headspace). The mole fraction of CO2 in the headspace gas is measured using a non-dispersive infrared (NDIR) analyzer from LICOR®.
The effects of water vapor on the sample analyses are kept to a minimum by removing as much water as possible. The water is first condensed out of the sample gas stream by cooling to ~5 °C using a thermoelectric device. Then water is further removed using Nafion® gas dryers before reaching the IR analyzer. The counterflow gas in the dryer is pre-dried outside air. Typical water content of the analyzed gas is less than 3 millimoles/mole with approximately 90% of the water being removed.
The infrared analyzer is calibrated regularly using four standard gases (240 – 520 ppm CO2 in air) from Scott-Martin Inc. (Riverside, CA). Before and after use in the field, the standards are calibrated using primary reference gases from the laboratory of Dr. Charles D. Keeling, which are directly traceable to the WMO scale. Any value outside the range of the standards should be considered approximate (+/-5 ppm). While individual data points above the highest standard or below the lowest standard may be less accurate, the general trends would be indicative of the seawater chemistry. The exact concentrations of the standards used on a particular cruise are listed in the individual readme file.
The system also measures the CO2 content of the outside air, which is drawn from an inlet on the box mast approximately 15 meters above the water. Atmospheric air is constantly being pulled (6 liters/min maximum flow) through ~60 meters of tubing (1 cm OD Dekoron) to the analytical system located in the Hydro Chem lab. The seawater is drawn from the ship’s flowing seawater line, which also feeds a thermosalinograph and Turner fluorometer.
The three CO2 standard cylinders come from Scott-Marrin, Inc., and are calibrated with primary standards that are directly traceable to the WMO scale. The zero gas is ultra-high purity air. Any value outside the range of the standards should be considered approximate (+/-5 ppm). While individual data points above the highest standard or below the lowest standard may be less accurate, the general trends would be indicative of the seawater chemistry. The standards used on a particular cruise are listed in the individual readme file.
When the first analytical system was in use (2008 – May 2010), a ‘Deck Box’ containing a high precision pressure transducer, a GPS and Iridium satellite modem was located outside and several decks above the system on part of the ship’s superstructure protected from severe weather. The instrumental system via the deck box recorded the atmospheric pressure and the position of the ship. The measured pressure is corrected for the height of the barometer above the sea surface with the addition of dgh/u – where d is atmospheric density (1.2 kg/m3), g is gravitational acceleration (9.8 m/sec2), h is height of thbarometer above the sea surface, and u is the conversion factor from pascals to desired pressure units. The estimated height of 15 meters results in a change in the barometric pressure of approximately of 1.8 mbar. When the second analytical system was is use, the barometric pressure and ship position was obtained from the ship’s sensors.
A typical sequence of continuous analyses is:
STEP TYPE REPETITIONS
1 – Standards (all four) – 1
2 – ATM – 5
3 – EQU – 60
With these settings, a complete set of standards and the atmospheric analyses are done every 3 hours and a full day contains about 480 analyses of the equilibrator headspace.
Calculations
The measured xCO2 values are linearly corrected for instrument response using the standard measurements (see Pierrot et al., 2009).
For ambient air and equilibrator headspace the fCO2a or fCO2eq is calculated assuming 100% water vapor content:
fCO2 = xCO2 P (1-pH2O) exp[(B11+2d12)P/RT]
where fCO2 is the fugacity in ambient air or equilibrator headspace, pH2O is the water vapor pressure at the sea surface or equilibrator temperature, P is the equilibrator or
outside atmospheric pressure (in atm), T is the SST or equilibrator temperature (in K) and R is the ideal gas constant (82.057 cm^3·atm·deg^-1·mol^-1). The exponential term is the fugacity correction where B11 is the first virial coefficient of pure CO2
B11 = -1636.75 + 12.0408 T – 0.0327957 T^2 + 3.16528E-5 T^3
and
d12 = 57.7 – 0.118 T</span?
is the correction for an air-CO2 mixture in units of cm^3·mol^-1 (Weiss, 1974).
The fugacity as measured in the equilibrator is corrected for any temperature difference between sea surface temperature and equilibrator chamber using the empirical correction outlined in Takahashi et al. (1993).
fCO2(SST) = fCO2(teq)exp[0.0423(SST-teq)]
where fCO2(SST) is the fugacity at the sea surface temperature and fCO2(teq) is the fugacity at the equilibrator temperature. SST and teq are the sea surface and equilibrator temperatures in degrees C, respectively.
The amount of time between the sea water passing by the SST (SBE38) sensor and the water flowing through the equilibrator is estimated before assigning an SST value to each analysis. The patterns in the temperature records for the equilibrator and for SST over time are compared, and a time offset that optimizes the match of these patterns is determined. The time offset is applied to the SST measurements. A linear interpolation between the time-adjusted SST data yields the SST value assigned to each CO2 analysis and used in the fugacity calculations.
Data File Structure
List of variables included in this dataset:
COLUMN
HEADER
EXPLANATION
1.
EXPOCODE
Expedition code, where ’33GG’ is the NODC ship identifier, and YYYYMMDD is the UTC date that the ship starts the expedition
2.
Group_Ship
AOML_GordonGunter, (if present)
3.
Cruise_ID
Dependent upon expedition’s name, (if present)
4.
YD_UTC
Decimal year day
5.
DATE_UTC_ddmmyyyy
UTC Date
6.
TIME_UTC_hh:mm:ss
UTC Time
7.
LAT_dec_degree
Latitude in decimal degrees (negative values are in southern hemisphere)
8.
LONG_ dec_degree
Longitude in decimal degrees (negative values are in western hemisphere)
9.
xCO2_EQU_ppm
Mole fraction of CO2 in the equilibrator headspace (dry) at equilibrator temperature, in parts per million
10.
xCO2_ATM_ppm
Mole fraction of CO2 in outside air (dry), in parts per million
11.
xCO2_ATM_interpolated_ppm
xCO2 in outside air associated with each water analysis. These values are interpolated between the bracketing averaged good xCO2_ATM analyses, in parts per million, (if present)
12.
PRES_EQU_hPa
Barometric pressure in the equilibrator headspace, in hectopascals (1 hPa = 1 millibar)
13.
PRES_ATM@SSP_hPa
Pressure measured by outside barometer, corrected to sea level, in hectopascals
14.
TEMP_EQU_C
Water temperature in equilibrator, in degrees centigrade
15.
SST_C
Sea surface temperature from the ship’s temperature sensor, in degrees centigrade [interpolated, see note above]
16.
SAL_permil
Salinity from the thermosalinograph (SBE45), on the Practical Salinity Scale
17.
fCO2_SW@SST_uatm
Fugacity of CO2 in sea water, in microatmospheres (100% humidity)
18.
fCO2_ATM_interpolated_uatm
Fugacity of CO2 in air corresponding to the interpolated xCO2, in microatmospheres (100% humidity), (if present)
19.
dfCO2_uatm
Sea water fCO2 minus interpolated air fCO2, in microatmospheres, (if present)
20.
WOCE_QC_FLAG
Quality control flag for fCO2 values (2 = good value, 3 = questionable value)
21.
QC_SUBFLAG
Quality control sub flag for fCO2 values provides explanation for atypical data, when QC_FLAG = 3
The quality control flags are provided as an aid to the interpretation of the CO2 data. Stringent minimum and maximum values for numerous parameters (e.g.temperature difference between the equilibrator temperature and SST) have been established by CO2 researchers (see Pierrot et al., 2009). These ranges were chosen so that if each parameter were within their stringent range, the resulting CO2 data would almost certainly be good. If a parameter is outside its range or if a parameter is estimated from surrounding good values, the quality flag of that data record is set to 3 (questionable value). The resulting CO2 data could be good; however, investigators should determine whether these data are valid for their purposes.
References
DOE (1994). OE (1994). Handbook of methods for the analysis of the various parameters of the carbon dioxide system in sea water; version 2. DOE.
Feely, R. A., R. Wanninkhof, H. B. Milburn, C. E. Cosca, M. Stapp and P. P. Murphy (1998). A new automated underway system for making high precision pCO2 measurements onboard research ships. Analytica Chim. Acta 377: 185-191.
Ho, D. T., R. Wanninkhof, J. Masters, R. A. Feely and C. E. Cosca (1997). Measurement of underway fCO2 in the Eastern Equatorial Pacific on NOAA ships BALDRIGE and DISCOVERER, NOAA data report ERL AOML-30, 52 pp., NTIS Springfield.
Pierrot, D., C. Neill, K. Sullivan, R. Castle, R. Wanninkhof, H. Luger, T. Johannessen, A. Olsen, R. A. Feely, and C. E. Cosca (2009). Recommendations for autonomous underway pCO2 measuring systems and data-reduction routines. Deep Sea Research II, 56: 512-522.
Wanninkhof, R. and K. Thoning (1993) Measurement of fugacity of CO2 in surface water using continuous and discrete sampling methods. Mar. Chem. 44(2-4): 189-205.
Weiss, R. F. (1970). The solubility of nitrogen, oxygen and argon in water and seawater. Deep-Sea Research 17: 721-735.
Weiss, R. F. (1974). Carbon dioxide in water and seawater: the solubility of a non-ideal gas. Mar. Chem. 2: 203-215.
Weiss, R. F., R. A. Jahnke and C. D. Keeling (1982). Seasonal effects of temperature and salinity on the partial pressure of CO2 in seawater. Nature 300: 511-513.
Takahashi, T., J. Olafsson, J. G. Goddard, D. W. Chipman, and S. C. Sutherland (1993). Seasonal variation of CO2 and nutrients in the high-latitude surface oceans: a comparative study, Global Biogeochem. Cycles, 7, 843-878.
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