CLIVAR Indian Ocean (I6S) 2008 Cruise

Readme File

Class of Data: Surface ocean carbon dioxide concentrations

Dataset Identifier: Expo Code 33RR20080204

Statement of how to cite dataset:

CLIVAR I6S website: http://www.aoml.noaa.gov/ocd/gcc/clivari6s

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 the AOML ocean carbon group receives fair credit

for our 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:

This cruise was part of the CLIVAR/CO2 repeat hydrography

program (see http://ushydro.ucsd.edu/). The Scripps Institution

of Oceanography's Research Vessel Roger Revelle departed Durban,

South Africa on February 4, 2008 entering the southward-flowing

Agulhas Current and traveled due south along a transect

coinciding with Longitude 30 East into the Antartic Circumpolar

Current down to the ice edge at 70 S returning to Cape Town,

South Africa on March 16, 2008.

Scientist responsible for technical quality of dataset:

Rik Wanninkhof

NOAA/AOML/Ocean Chemistry Division

4301 Rickenbacker Causeway

Miami, Florida 33149

Rik.Wanninkhof@noaa.gov

Contact person for this dataset:

Esa Peltola

NOAA/AOML/Ocean Chemistry Division

4301 Rickenbacker Causeway

Miami, Florida 33149

Esa.Peltola@noaa.gov

Timestamp for initial submission of dataset: 4/27/08

Timestamp for the most recent update of dataset: 4/27/08

Timestamp period the dataset refers to: 2/05/2008 - 3/14/2008

Geographic area the dataset refers to:

30 S to 70 S

20 E to 35 E

List of variables included in this dataset:

COLUMN HEADER EXPLANATION

1\. GROUP/SHIP: AOML_Revelle.

2\. CRUISE_DESIGNATION: IO6S(2008)\_33RR20080204

3\. JD_GMT: Decimal year day.

4\. DATE_DDMMYYYY: The date format has been changed from

previous files to conform with the IOCCP

recommendations.

5\. TIME_HH:MM:SS: GMT time. Local time = GMT time + 2 hours.

6\. LAT_DEC_DEGREE: Latitude in decimal degrees (negative

values are in the southern hemisphere).

7\. LONG_DEC_DEGREE: Longitude in decimal degrees (negative

values are in the western hemisphere).

8\. xCO2W_PPM: Mole fraction of CO2 (dry) in the

headspace equilibrator at equilibrator

temperature (Teq) in parts per million.

9\. xCO2A_PPM: Mole fraction of CO2 in air in parts per

million.

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

centigrade. 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_L/MIN: Water flow through equilibrator in liters

per minute.

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 centigrade.

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 the pressure in the lab

(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.

20\. SHIP_SPEED_KNOT: Ship\'s speed from ship\'s navigation system in

knots.

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.

22\. WIND_SPEED_REL_M/S: Wind speed relative to the ship from

ship\'s navigation system in meters per

second.

23\. fCO2W@SST_uATM: Fugacity of CO2 in sea water in

microatmospheres.

24\. QC_FLAG_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\. QC_FLAG_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. There is no fluorometer data for this

cruise.

29\. WIND_SPEED_TRUE_M/S: True wind speed in meters per second.

30\. WIND_DIR_TRUE_DEGREE: True wind direction in degrees were

0 = North and 90 = East.

31\. AIR_TEMP_C: Outside air temperature from ship\'s

computer system in degrees centigrade.

The following fields have been QC\'ed by the CO2 group:

GROUP_SHIP

CRUISE

JD_GMT

DATE_DDMMYYYY

TIME_HH:MM:SS

LAT_DEC_DEGREE

LONG_DEC_DEGREE

xCO2W_PPM

xCO2A_PPM

PRES_EQUIL_hPa

EQTEMP_C

WATER_FLOW_L/MIN

GASFLOW_IR_ML/MIN

TEMP_IR_C

PRES_IR_hPa

fCO2W@SST_uATM

QC_FLAG_WATER

The following fields are from the ship\'s onboard systems and the
quality

of this data cannot be verified:

PRES_SEALEVEL_hPa

SST(TSG)\_C

SAL(TSG)\_PERMIL

SHIP_HEADING_TRUE_DEGREE

SHIP_SPEED_KNOT

WIND_DIR_REL_DEGREE

WIND_SPEED_REL_M/S

FLUORO_uG/L

WIND_SPEED_TRUE_M/S

WIND_DIR_TRUE_DEGREE

AIR_TEMP_C

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 equilibration chamber. The chamber contains a

water spray head, an enclosed gaseous headspace (\~ 850 ml), and

a pool of seawater (\~ 750 ml) 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:

fCO2a/eq = xCO2a/eq(P-pH2O)exp(B11+2d12)P/RT

where fCO2a/eq is the fugacity in ambient air or 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

0.2 °C warmer than sea surface temperature. The empirical

temperature correction from equilibrator temperature to SST is

outlined in Takahashi et al (1993):

fCO2w = fCO2eq Exp(0.0423 (SST-Teq))

INSTRUMENT DESIGN:

The general principle of instrumental design can be found in Wanninkhof

and Thoning (1993), Ho et al. (1995), and Feely et al. (1998). The

analyses are done with an infrared analyzer calibrated with three

standard gases spanning the anticipated range of water and air values.

The standard gases come from NOAA/CMDL in Boulder and are directly

traceable to the WMO scale.

The standards used on the cruise are:

STANDARD TANK \# CONCENTRATION VENDOR

STD1 CA06827 284.71 CMDL

STD2 CA05334 380.98 CMDL

STD3 CA06380 448.29 CMDL

Salinity, SST, wind direction (both absolute and relative), wind speed

(both absolute and relative), ship speed, ship course, sealevel

pressure, air temp, latitude and longitude data are from the

ship's MET system log files.

Sampling Cycle:

The system runs on an hourly cycle during which 3 standard gases, 3

air samples from the bow tower and 8 surface water samples (from the

equilibrator head space) are analyzed on the following schedule:

Mins. after hour Sample

================ ======

3.5 Low Standard

7.5 Mid Standard

11.5 High Standard

16.24 Water

20.5 Water

25.2 Water

29.5 Water

33.5 Air

37.5 Air

41.5 Air

46.2 Water

50.5 Water

55.2 Water

59.5 Water

Units:

All xCO2 values are reported in parts per million (ppm) and fCO2 values

are reported in microatmospheres (uatm) assuming 100 % humidity at the

equilibrator temperature for fCO2w and for SST at fCO2a.

Estimated overall uncertainty of measurement:

The xCO2eq measurements are believed accurate to 1 ppm. The fCO2@SST

measurements are believed to be precise to 2 ppm.

Bibliography:

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.

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.

DATA QC:

The data for the following year days (JD) were initialized to --999.99

due to low water flow:

JD

29.996

29.996

29.996

30.002

30.002

30.002

30.035

30.036

32.756

32.756

The data for the following year days (JD) were removed due to low gas

flow:

JD

74.044

74.047

74.050

74.053

74.056

74.059

74.062

74.065

74.068

74.071

74.074

74.077

74.080

74.083

74.086

74.089

74.092

74.095

74.098

74.101

74.104

74.107

74.110

74.112

74.116

74.119

74.122

74.125

74.128

74.130

74.133

74.136

74.139

74.143

74.146

74.149

74.151

74.154

74.157

74.160

74.163

74.167

74.169

74.172

74.175

74.178

74.181

74.184

74.187

74.190

74.193

74.196

74.199

74.202

74.205

74.208

74.211

74.214

74.217

74.220

74.223

74.226

74.229

74.232

74.235

74.237

74.241

74.244

74.247

74.250

74.253

74.255

74.258

74.261

74.264

74.268

74.271

74.274

74.276

74.279

74.282

74.285

74.288

74.292

74.294

74.297

74.300

74.303

74.306

The salinity data for the following year days (JD) were removed

(initialized to --999.99): JD 43.309 to JD.375.

The questionable fCO2a data for the following year days (JD) were

removed due to stack gas contamination: JD 36.357 to JD 37.083,

JD 38.761 to JD 38.875, JD 38.970 to JD 39.125, JD 43.428 to

JD 43.458, JD 61.095 to JD 61.167, and JD 65.470 to JD 65.500.

There was a problem with the SST (SCS temperature) from JD 40.4166

to JD 43.3777. The SST data for this time interval was estimated

in the following manner: The average difference between Tequil

and SST for 100 points immediately before and after the data

dropout was determined. This difference was subtracted from

the Tequil to create a SST. The correction (the average difference

of the Tequil and SST) was 0.17319 C.

There was a problem with the sealevel pressure from JD 35 to JD 45.

A correction (the average difference between the equilibrator pressure

and the sealevel pressure) was applied to the sealevel pressure

utilizing the equilibrator pressure in the same manner as described

above for SST. In this time interval, the sealevel pressure was

determined assuming sealevel pressure = equilibrator pressure --

1.102 MB.

The following SST and Equilibrator temperature values were interpolated

using the values immediately preceding and following the data dropout:

45.244

48.362

54.360

73.354

The following Equilibrator temperature values were interpolated using

the values immediately preceding and following the data dropout:

50.818

51.559

52.538

54.362

56.297

59.982

63.056

63.059

The following Salinity values were interpolated using the values

immediately preceding and following the data dropout:

58.198

59.089

59.086

67.273

The following SST values were interpolated using the values

Immediately preceding and following the data dropout:

45.244

48.362

49.026

50.285

54.359

56.024

56.681

57.294

57.595

57.896

58.514

58.803

59.086

59.341

60.589

60.717

60.660

61.029

61.274

61.735

66.577

66.785

67.047

73.354