AOML » GCC » Ongoing R/V BALDRIGE Data

The electronic data in comma delimited ASCII form (.CSV) can be accessed by
entering the year under the "R/V BALDRIGE Data" prompt to the left and then entering "GO".

A complete list of the data can be found at:

"http://www.aoml.noaa.gov/ocd/gcc/rvbaldrige_cruiseinventory.php"

For further information or special requests regarding the R/V BALDRIGE data contact:

Betty Huss
Atlantic Oceanographic and Meteorological Lab
4301 Rickenbacker Causeway
Miami, FL 33149

email: betty.huss@noaa.gov
Phone: 305-361-4395

****************** Use of AOML CO2 Underway Data **************************
* [Adapted from NOAA Climate Monitoring and Diagnostics Laboratory (CMDL) *
************* Carbon Cycle Greenhouse Gasses (CCGG) web site] *************

These data are made freely available to the public and the scientific community
in the belief that their wide dissemination will lead to greater understanding
and new scientific insights. The availability of these data does not
constitute publication of the data. We rely on the ethics and integrity of the
user to assure that AOML receives fair credit for our work. Please send
manuscripts using this data to AOML for review before they are submitted for
publication so we can insure that the quality and limitations of the data are
accurately represented.

*********************** Reciprocity Agreement *****************************
* [Adapted from NOAA Climate Monitoring and Diagnostics Laboratory (CMDL) *
************* Carbon Cycle Greenhouse Gasses (CCGG) web site] *************

Use of these data implies an agreement to reciprocate. Laboratories making
similar measurements agree to make their own data available to the general
public and to the scientific community in an equally complete and easily
accessible form. Modelers are encouraged to make available to the community,
upon request, their own tools used in the interpretation of the AOML data,
namely well documented model code and any additional information necessary for
other scientists to repeat the work and to run modified versions.

***************************************************************************

The R/V BALDRIGE cruise data files conform to the recommendation of the
International Ocean Carbon Coordination Project (http://ioc.unesco.org/ioccp).
The purpose of this project is to standardize measurement techniques and QA/QC
procedures, coordinate international ocean carbon observations, and improve
accessibility to carbon data sets in order to better meet the needs of the
research community. Many of the auxillary data fields were not measured
(or retained) in the original data files; therefore, many of the fields
contain default values.

COLUMN HEADER EXPLANATION
1. Group/Ship: AOML_Baldrige for all R/V BALDRIGE data.

2. Cruise_Designation: Cruise Name.

3. JD_GMT: Decimal year day (same as in old files).

4. Date_DDMMYYYY: The date format has been changed to comply
with the IOCCP recommendations.

5. Time_HH:MM: GMT 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. xCO2w_ppm: Mole fraction of CO2 (dry) in the headspace
equilibrator at equilibrator temperature (Teq)
in parts per million. Water comes from bow
intake 2 m below the water line.

9. xCO2a_ppm: Mole fraction of CO2 in air in parts per million
(NEW). This field is not measured on the Explorer
of the Seas - all fields initialized to -9.

10. Pres_Equil_hPa: Barometric pressure in the lab in hectopascals
(1 hectopascal = 1 millibar).

11. Pres_sealevel_hPa: Barometric pressure from ship's barometer,
corrected to sea level in hectopascals (1
hectopascal = 1 millibar).

12. EqTemp_C: Temperature in equilibrator water in degrees
centigade. Temperature in equilibrator measured
with a calibrated thermistor.

13. SST(TSG)_C: Temperature from the ship's thermosalinograph in
degrees centigrade.

14. Sal(TSG)_Permil: Salinity from the ship's thermosalinograph on the
Practical Salinity Scale.

15. Water_flow_1/min: Water flow through equilibrator in liters per
minute. This field was not measured on the
R/V BALDRIGE - all fields initialized to -9.

16. Gasflow_IR_ml/min: Gas flow through the Licor infrared analyzer before
the flow is stopped in milliliters per minute.

17. Temp_IR_C: Temperature of the Licor infrared analyzer sample
cell in degrees centrigrade. This field was not
measured on the R/V BALDRIGE - all fields
initialized to -9.

18. Pres_IR_hPa: Pressure in the Licor infrared analyzer in
hectopascals. NOTE: There is no pressure sensor
in the Licor but since it is vented to atmosphere
prior to measurement, this value is the same as
number 10 above. (1 hectopascal = 1 millibar).

19. Ship_heading_true_degree: Ship's heading from ship's navigation system in
degrees with 0 = North and 90 = East. This field
was not measured on the R/V BALDRIGE - all
fields intialized to -9.

20. Ship_speed_knot: Ship's speed from ship's navigation system in
knots. This field was not measured on the
R/V BALDRIGE - all fields initialized to -9.

21. Wind_dir_rel_degree: Wind direction relative to the ship from ship's
navigation system in degrees with 0 = from the bow
and 90 = from starboard. This field was not
measured on the R/V BALDRIGE - all fields
initialized to -9.

22. Wind_speed_rel_m/s: Wind speed relative to the ship from ship's
navigation system in meters per second. This
field was not measured on the R/V BALDRIGE -
all fields initialized to -9.

23. fCO2W@SST_uatm: Fugacity of CO2 in sea water in microatmospheres
calculated as outlined below.

24. QcFlag_water: Quality control flag for sea water xCO2 and fCO2
values with 2 = good value, 3 = questionable value,
4 = bad value, and 9 = no measurement taken.

25. fCO2a_uatm: Fugacity of CO2 in air in microatmospheres.

26. QcFlag_air: Quality control flag for air xCO2 and fCO2 with
2 = good value, 3 = questionable value,
4 = bad value, and 9 = no measurement taken.

27. dfCO2_uatm: Sea water fCO2 - air fCO2 in microatmospheres.
This uses the average air value for the current hour.

28. Fluoro_ug/l: Reading from the fluorometer in micrograms per liter.
This field is not measured on the R/V BALDRIGE -
all fields initialized to -9.

29. Wind_speed_true_m/s: True wind speed in meters per second. This
field is not measured on the R/V BALDRIGE -
all fields initialized to -9.

30. Wind_dir_true_degree: True wind direction in degrees were 0 = North
and 90 = East. This field is not measured on
the R/V BALDRIGE - all fields initialized to -9.

31. Air_Temp_C: Outside air temperature from ship's computer
system in degrees centrigrade. This field is
not measured on the R/V BALDRIGE - all fields
initialized to -9.

*********************************************************************************

Standard Gases and Reference Gas: The three standard gases come from NOAA/CMDL,
now called the Global Monitoring Division of the Earth Research Laboratory,
and are directly traceable to the WMO scale. The uncertainity of assigned
value of each calibration gas is based on pre and post cruise calibrations
and is less than 0.05 ppm.

List of calibration gases used on the R/V BALDRIGE cruises are:

SATL 91 Legs 1 and 2 (OACES_91L1 and OACES_91L2):
STANDARD CONCENTRATION VENDOR
STD1 300 CMDL
STD2 350 CMDL
STD3 400 CMDL

ACCP 92:
STANDARD CONCENTRATION VENDOR
STD1 281 CMDL
STD2 356 CMDL
STD3 422 CMDL

ASTEX 92:
STANDARD CONCENTRATION VENDOR
STD1 281 CMDL
STD2 356 CMDL
STD3 422 CMDL

EqPac Spring 92:
STANDARD CONCENTRATION VENDOR
STD1 300 CMDL
STD2 350 CMDL
STD3 400 CMDL

EqPac Spring 93:
STANDARD CONCENTRATION VENDOR
STD1 294.45 CMDL
STD2 355.30 CMDL
STD3 422.04 CMDL

NATL 93:
STANDARD CONCENTRATION VENDOR
STD1 305.56 CMDL
STD2 356.20 CMDL
STD3 404.73 CMDL

EqPac Spring 94:
For work in the equatorial upwelling zone (2 North to 10 South
in the eastern Equatorial Pacific):
STANDARD TANK# CONCENTRATION VENDOR
STD1 106619 356.20 CMDL
STD2 114979 404.73 CMDL
STD3 106643 524.87 CMDL

For work north of the equator, a narrower range was used:
STANDARD TANK# CONCENTRATION VENDOR
STD1 115001 313.94 CMDL
STD2 106619 356.20 CMDL
STD3 114979 404.73 CMDL

EqPac Fall 94:
For work in the equatorial upwelling zone (2 North to 10 South
in the eastern Equatorial Pacific):
STANDARD TANK# CONCENTRATION VENDOR
STD1 106619 356.20 CMDL
STD2 114979 404.73 CMDL
STD3 ? 521.26 CMDL

For work north of the equator, a narrower range was used:
STANDARD TANK# CONCENTRATION VENDOR
STD1 115001 313.94 CMDL
STD2 106619 356.20 CMDL
STD3 114979 404.73 CMDL

Indian Ocean 95 Leg 1 - Leg 8c (mb95-01 - mb95-08c):
STANDARD CONCENTRATION VENDOR
STD1 300 CMDL
STD2 360 CMDL
STD3 420 CMDL

*********************************************************************************

CO2 ANALYTICAL SYSTEM:

The concentration of carbon dioxide (CO2) in surface ocean water is determined by
measuring the concentration of CO2 in gas that is in contact with the water. Surface
water is pumped from an inlet in the ship's bow to the equilbration chamber. The
equilbration chamber has an enclosed volume of gas, or headspace, and a pool of seawater
that continuously overflows to a drain. As the water flows through the chamber, the
dissolved gases (like CO2) partition between the water and the headspace. At equilibrium,
the ratio of CO2 in the water and in the headspace is influenced most by temperature,
and that relationship is known. By measuring the concentration of CO2 in the headspace
and the temperature in the chamber, the partial pressure (or fugacity) of CO2 in the
surface water can be calculated.

CALCULATIONS:

The mixing ratios of ambient air and equilibrated headspace air are calculated by fitting a
second-order polynomial through the hourly averaged response of the detector versus mixing
ratios of the standards. Mixing ratios of dried equilibrated headspace and air are
converted to fugacity of CO2 in surface seawater and water saturated air in order to
determine the fCO2. For ambient air and equilibrator headspace the fCO2a, or fCO2eq is
calculated assuming 100% water vapor content:

fCO2eq = xCO2eq(P-pH2O)exp(B11+2d12)P/RT

where fCO2eq is the fugacity in the equilibrator, pH2O is the water vapor
pressure at the sea surface temperature, P is the 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 second virial coefficient of pure CO2

B11 = -1636.75 + 12.0408T - 0.032795T^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^3·mol^-1 (Weiss, 1974).

The calculation for the fugacity at SST involves a temperature correction term for the
increase of fCO2 due to heating of the water from passing through the pump and through
5 cm ID PVC tubing within the ship. The water in the equilibrator is typically 0.4 °C
cooler than sea surface temperature. The empirical temperature correction from
equilibrator temperature to SST is outlined in Weiss et al. (1982).

dln(fCO2)=(teq-SST)(0.0317-2.7851E-4 teq - 1.839E-3 ln(fCO2eq))

where dln(fCO2) is the difference between the natural logarithm of the fugacity at teq
and SST, and teq is the equilibrator temperature in degrees C.

NOTES ON DATA:
Columns have a default value of -9 in case of instrument malfunction, erroneous
readings or missing data except for the dfCO2_uatm (column 27) that uses -999.99
to avoid confusion with actual fCO2 differences of -9. Furthermore, if a suspicious
xCO2 value, pressure or temperature value is encountered, the fCO2 is not
calculated.

INSTRUMENT DESCRIPTION

Two different instruments were used on the R/V BALDRIGE cruises. The
instrument used from 1991 through 1993 is described in detail in Wanninkhof
and Thoning (1993), while the system used in 1994 and 1995 is described in
the data reports by Ho et al. (1995) and Masters et al. (1997). The data
reports (AOML-30 and AOML-31) can be downloaded in pdf format at http://
www.aoml.noaa.gov/ocd/oaces/bottle_data.html. Both systems operate
under the same principals outlined below with an hourly calibration routine
and a constant flow of reference gas (standard 1) through the reference
cell to yield differential measurements. Headspace air flow was configured
differently in the two systems and the older system measured the equilibrator
headspace more frequently. On the older system, system 1.0, two equilibrator
headspace ("water") values were captured each hour and one ambient air
sample was analyzed. The water samples were averaged and merged with
the air value to yield a single value per hour in the database. On the
new system, system 1.5, eight water samples were measured per hour and three
air samples were analyzed. The air samples were averaged and merged with
the eight water samples yielding eight analyses of fCO2 per hour.

The concentration of CO2 in the headspace gas is measured using the adsorption of
infrared (IR) radiation, which results from changes in the rotational and vibrational
energy state of the CO2 molecule. The LI-COR detector passes IR radiation through
two 6" cells. The reference cell is flushed with a gas of known CO2 concentration.
The sample cell is flushed with the headspace gas. A vacuum-sealed, heated filament
is the broadband IR source. The IR radiation alternates between the two cells via
a chopping shutter disc spinning at 500 Hertz. An optical filter selects an adsorption
band specific for CO2 (4.26 micron) to reach the detector. The solid state (lead
selenide) detector is kept at -12 degrees C for excellent stability and low signal noise
(less than 0.2 ppm).

Several steps are taken to reduce interferences and to increase the accuracy of the
measurements. The IR adsorption band for water vapor is close to the band for CO2.
After the equilibration chamber, the headspace travels through a drying trap to
remove water vapor. During each analysis, the headspace gas is compared to a reference
gas of known concentration. To improve the accuracy of the measurements, three
different gaseous standards for CO2 are analyzed once an hour instead of the
headspace gas.

Analyzer: LI-COR 6252 (analog output) infrared (IR) analyzer.

Method of Analysis: Differential analyses relative to a reference gas which is
close to the CO2 concentration of the middle standard. Measures dried equilibrator
headspace gas. Gas flow is stopped prior to IR readings.

Drying Method: The equilibrator headspace sample gas first goes through an air filter
and a thermoelectric refrigerator (~6 C). The sample and standard gases pass through
a Perma Pure (Nafion) dryer and a short column of magnesium perchlorate before reaching
the analyzer. The counter flow in the Perma Pure tube is the reference gas.

Equilibrator (setup, size, flows): The equilibrator on the R/V BALDRIGE cruises
was a Weiss style Plexiglass showerhead equilibrator that has an internal volume
of about 24-1 with 1/3 water and 2/3 headspace. Seawater from a clean sampling
line originating at the bow of the ship was showered into the equilibrator where
the headspace gas comes into equilibrium with the water. During 1991 and 1992
the water flow into the equilibrator was 15 to 20 l/min. The high degree of
turbulence at this flow caused bubbles to escape through the water drain and
lab air was drawn into vents causing approximately 1% bias in the values (see
NOAA technical memorandum AOML-85 Chen et al. 1995). For 1993 and beyond, the
water flows were decreased to 8 to 13 l/min. For system 1.0, headspace air was
recirculated at a flow of 5 l/min and 50 to 75 ml/min was shunted off during
the headspace anaylsis cycle and vented from the detector. For system 1.5, 80
to 150 ml/min of gas was recirculated through the IR detector and back into
the equilibrator.

Additional sensors:
The 10-cm thermistor used to electronically log the temperature was mounted in
the bottom of the equilibrator. It was calibrated annually against a Guildline
model 9540 digital platinum resistance thermometer with a NIST traceable probe.
Temperatures are believed accurate to 0.02 °C.

The barometric pressure was measured in the lab next to the equilibrator with a
Setra model 370 electronic barometer with an accuracy of ± 0.2 hPa. Periodic
comparison of barometers gave readings within ± 0.5 hPa. The equilibrator had
two 0.5-cm ID vents to the laboratory and thus equilibrator headspace pressure
was assumed to be laboratory pressure.

A Seabird SBE 21 thermosalinograph was mounted in the bow chamber 3 m from the
intake at nominally 3-m depth. The unit was calibrated annually and provided
SST to better than 0.02 °C and salinity generally better than 0.1.

Sampling Cycle:
The system runs on an hourly cycle during which 3 standard gases, surface
water samples (from the equilibrator head space) and bow air are analyzed
on a system dependent schedule listed in the individual readme files.

REFERENCES:

Chen, H., R. Wanninkhof, R.A. Feely, and D. Greeley, Measurement of fugacity of
carbon dioxide in sub-surface water: an evaluation of a method based on infrared
analysis, NOAA technical report ERL AOML-85, 52 pp, NOAA/AOML, 1995.
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.
Masters, J.C., R.H. Wanninkhof, D.T. Ho, M. Steckley, R.A. Feely, and C. Cosca.
Continuous air and surface seawater measurements of fCO2 on board the NOAA ship
Malcolm Baldrige around-the-world cruise in 1995. NOAA Data Report, ERL AOML-31
(PB98-105950), 80 pp. 1997
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.

R/V BALDRIGE Master Readme File