R/V Knorr Master Readme
The information presented in this file is applicable to all the data sets
collected on the R/V Knorr. Any temporary changes in this information
will be noted in the readme files for the individual expeditions.
Class of Data: Surface ocean carbon dioxide concentrations
Statement of how to cite dataset:
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
insure that the AOML ocean carbon group receives fair credit for its work.
Please consult with us prior to use so we can insure that the quality and
limitations of the data are accurately represented.
Cruise Information:
FASTEX 1996-1997 Cruise: See the FASTEX readme file for details
on this cruise www.aoml.noaa.gov/ocd/gcc/knorr/fastex/fastex_readme.txt
International Polar Year ICEALOT 2008 Cruise:
This cruise was part of POLARCAT Experiment for the International Polar Year
2008. The International Chemistry Experiment in the Arctic Lower Troposphere
(ICEALOT) investigated the springtime sources and transport of pollutants to
the Arctic, evolution of aerosols and gases into and within the Artic and
climate impacts of haze and ozone in the Arctic.
The cruise was completed via two legs aboard the Woods Hole Oceanographic
Institute research vessel Knorr. Leg #1 left Woods Hole, Massachusetts,
on 19 March and arrived in Tromso, Norway, on 12 April, 2008. Leg #2
left Tromso on 13 April and arrived in Reykjavik, Iceland, on 24 April,
2008. The underway pCO2 instrument was installed by Denis Pierrot and
was maintained by the Knorr's Shipboard Scientific Services Group (SSSG),
especially technician Amy Simoneau. The SSSG provided data collected by
the ship's meteorological and atmospheric sensors in support of the cruise.
Lead scientists for the ICEALOT cruise:
Patricia Quinn and Tim Bates
NOAA/PMEL/Atmospheric Chemistry Group
7600 Sand Point Way NE
Seattle, WA 98115
Patricia.K.Quinn@noaa.gov
Tim.Bates@noaa.gov
International Polar Year NAB08 Cruise:
The cruise was part of North Atlantic Bloom Experiment 08 Collaboratory
(NAB08) - see website. NAB08 undertook autonomous measurements of carbon
fluxes via floats and gliders equipped with biogeochemical sensors in the
North Atlantic Bloom. Extensive shipboard measurements were done to compare
with and to complement the autonomous measurements.
The study area was centered at approximately 61 N and 26 W and covered 20000
km2. The Woods Hole Oceanographic Institute research vessel Knorr departed
Reykjavik, Iceland, on 1 May and returned on 22 May, 2008. The underway pCO2
instrument was installed by Denis Pierrot on 17 March before a previous science
expedition, and it remained in operation through the transit leg back to the
USA after the NAB08 cruise. The continued operation was possible because of
the care and maintenance by the Knorr's Shipboard Scientific Services Group
(SSSG), especially technician Amy Simoneau. The SSSG provided data collected
by the ship's meteorological and atmospheric sensors in support of the cruises.
Lead scientists for NAB08 cruise:
Eric D'Asaro and Craig Lee
University of Washington/Applied Physics Lab
1013 NE 40th Street
Seattle, WA 98115
dasaro@apl.washington.edu
craig@apl.washington.edu
Mary Jane Perry
University of Maine
Darling Marine Center
Walpole, MA 04573
perrymj@maine.edu
Scientists responsible for the technical quality of this pCO2 dataset:
Rik Wanninkhof and Denis Pierrot
NOAA/AOML/Ocean Chemistry Division
4301 Rickenbacker Causeway
Miami, FL 33149
Rik.Wanninkhof@noaa.gov
Denis.Pierrot@noaa.gov
Contact persons for this dataset:
Kevin Sullivan and Denis Pierrot
NOAA/AOML/Ocean Chemistry Division
4301 Rickenbacker Causeway
Miami, FL 33149
Kevin.Sullivan@noaa.gov
Denis.Pierrot@noaa.gov
INSTRUMENT DESCRIPTION and CONFIGURATION:
The general principle of operation of the instrument can be found in Wanninkhof
andThoning (1993), Ho et al. (1995), Feely et al. (1998), and Pierrot et al.
(2008). Seawater flows through an equilibrator chamber where CO2 exchanges
between water and the air above it. An overflow pipe that is loosely covered
with an inverted cup maintains the continuously-flushed pool of seawater (~750 ml).
Small changes in seawater CO2 concentration are rapidly translated into changes
in CO2 concentration in the air of the chamber (~850 ml of enclosed 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 signal are compensated for by the analyzer
but are also kept to a minimum by removing as much water as possible. The
water is firstcondensed out of the gas stream by cooling. Water vapor is
further removed using Naphion® gas dryers before reaching the NDIR
analyzer. The sample gases typically contain less than 3 millimoles/mole
of water when they flow through the analyzer.
During the cruise the NDIR analyzer was calibrated regularly using three
standard gases from Scott-Martin Inc. (SMI) in Riverside, CA, and one
standard gas cylinder from NOAA's Earth System Research Laboratory (ESRL),
Global Monitoring Division in Boulder, CO. Before and after use in the
field, the SMI standards are calibrated using primary reference gases
from the laboratory of the late Dr. Charles D. Keeling. The Keeling
standards as well as the ESRL standards are directly traceable to the
WMO scale.
STANDARD SOURCE CYLINDER# CONCENTRATION(ppm)
STD1 SMI JA02267 247.72
STD2 SMI JA02264 317.86
STD3 SMI JA02285 372.47
STD4 ESRL CA01491 508.38
The system also measured the CO2 content of the outside air, which was drawn
from an inlet on the bow mast. Atmospheric air was constantly being pulled
(6 liters/min maximum flow) through ~200 feet of tubing (3/8" OD Dekoron)
to the analytical system located in the port aft corner of the main lab.
The seawater was drawn from the ship's flowing seawater line which also
fed a nearby thermosalinograph (Sea-Bird SBE45), which was provided and
maintained by the ship. The ship also provided a remote, hull-mounted
temperature sensor (Sea-Bird SBE48) for measurement of sea surface
temperature (SST).
A 'Deck Box' containing a high precision pressure transducer, a GPS and
Iridium satellite modem was located outside on the ship's superstructure
directly above the system. Through the deck box, the system recorded
the atmospheric pressure and the position of the ship. The measured
pressure was 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 the barometer above the sea surface, and u is the conversion factor
from pascals to desired pressure units. The estimated height of 5
meters resulted in a change in the barometric pressure of approximately
of 0.6 mbar.
The sequence of continuous analyses was:
STEP TYPE REPETITIONS
1 Span gas 1
2 Standards 1
3 ATM 5
4 EQU 100
5 Loop to STEP 2 10
6 Fresh water cleaning 1
7 Standards 1
8 Loop to STEP 1 1
The amount of time between analyses depended on whether the analyses were of the
same type of gas (e.g., STD, ATM, EQU) or not. When switching between different
gases, the connecting tubes and analyzer were flushed for an initial interval
called the 'PRE-FLUSH' time plus an interval called the 'REGULAR FLUSH' time.
Between successive measurements of the same type of gas, the system was flushed
for only the 'REGULAR FLUSH' time. The gas flow was then stopped, and after
the 'STOP FLOW' time interval, the output of the NDIR analyzer was read. The
pre-flush time was set to 180 seconds, the regular flush time was set to 60
seconds, and the stop flow time was set to 10 seconds for all types of gas.
With these settings, a complete set of standards and the atmospheric analyses
are done every 2.8 hours and a full day contained about 850 analyses of the
equilibrator headspace.
CALCULATIONS:
The measured xCO2 values are linearly corrected for instrument response using
the standard measurements.
For ambient air and equilibrator headspace the fCO2_ATM or fCO2_SW 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, 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^3ˇatmˇdeg^-1ˇmol^-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
is the correction for an air-CO2 mixture in units of cm^3ˇmol^-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.
REFERENCES:
DOE (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, R., H. Lüger,
T. Johannessen, A. Olsen, R. A. Feely, C. E. Cosca, 2009.
Recommendations for autonomous underway pCO2 measuring systems and
data reduction routines, Deep Sea Res, accepted .
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.
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.
METADATA:
List of variables included in this dataset:
COL HEADER EXPLANATION
1. Group_Ship AOML_Knorr
2. Cruise_ID dependent upon expedition's name
3. JD_GMT Decimal year day
4. DATE_UTC_ddmmyyyy UTC Date
5. TIME_UTC_hh:mm:ss UTC Time
6. LAT_dec_degree Latitude in decimal degrees (negative
values are in southern hemisphere)
7. LONG_ dec_degree Longitude in decimal degrees (negative
values are in western latitudes)
8. xCO2_EQU_ppm Mole fraction of CO2 in the equilibrator
headspace (dry) at equilibrator
temperature, in parts per million
9. xCO2_ATM_ppm Mole fraction of CO2 in outside air (dry),
in parts per million
10. 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
11. PRES_EQU_hPa Barometric pressure in the equilibrator
headspace, in hectopascals (1 hPa = 1 millibar)
12. PRES_ATM@SSP_hPa Pressure measured by outside barometer,
corrected to sea level, in hectopascals
13. TEMP_EQU_C Water temperature in equilibrator, in
degrees centigrade
14. SST_C Sea surface temperature from the ship's
remote temperature sensor, in degrees centigrade
[interpolated, see note below]
15. SAL_permil Salinity from the thermosalinograph
(SBE45), on the Practical Salinity Scale
16. fCO2_SW@SST_uatm Fugacity of CO2 in sea water, in
Microatmospheres (100% humidity)
17. fCO2_ATM_interpolated_uatm Fugacity of CO2 in air corresponding to the
interpolated xCO2, in microatmospheres
(100% humidity)
18. dfCO2_uatm Sea water fCO2 minus interpolated air fCO2,
in microatmospheres
19. WOCE_QC_FLAG Quality control flag for fCO2 values
(2 = good value, 3 = questionable value)
20. 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. The ship's data (columns 14 and 15) were used in calculation of the
fugacities and are included as a reference. The SSSG for the Knorr should be
contacted for additional information about those data.
The amount of time between the sea water entering the ship and flowing through
the equilibrator is estimated before assigning an SST value to each analysis.
The patterns in the temperature records for the equilibrator and SST over time
were compared. A time offset is applied to the SST data to optimize the match
of the patterns. A final linear interpolation between the time-adjusted SST
measurements is done to get the SST for each CO2 analysis.
