CLIVAR Indian Ocean (I8S) 2007 Cruise

Readme File

Class of Data: Surface ocean carbon dioxide concentrations

Dataset Identifier: Expo Code 33RR20070204

Statement of how to cite dataset:

CLIVAR I8S website: http://www.aoml.noaa.gov/ocd/gcc/clivari8s

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

Dunedin, New Zealand on 4 February 2007 with a long steam south

bringing the ship as close to Antarctica as ice and weather would

permit. The cruise ended in Fremantle, Australia on 16 March 2007

having completed all the WOCE 1995 I8S line along with an extension

to the Antarctic continental shelf. Underway surface pCO2, temperature

conductivity, dissolved oxygen, fluorometer, meteorological and

multibeam acoustical bathymetric measurements were made.

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:

Robert Castle

NOAA/AOML/Ocean Chemistry Division

4301 Rickenbacker Causeway

Miami, Florida 33149

Robert.Castle@noaa.gov

Timestamp for initial submission of dataset: 8/8/08

Timestamp for the most recent update of dataset: 8/8/08

Timestamp period the dataset refers to: 2/04/2007 - 3/16/2007

Geographic area the dataset refers to:

28 S to 66 S

80 E to 172 E

List of variables included in this dataset:

COLUMN HEADER EXPLANATION

1\. GROUP/SHIP: AOML_Revelle.

2\. CRUISE_DESIGNATION: IO8S(2007)\_33RR20070204

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 +12/+8 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), sealevel pressure, air temp, latitude and
longitude data are from the ship's MET system log files. Ship speed and

ship course are missing.

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 questionable fCO2W@SST data for the following year days (JD) were

removed (initialized to --999.99):

JD

41.327

45.667

45.678

47.095

48.389

48.931

49.699

49.702

49.979

50.521

51.011

51.014

52.479

53.699

54.143

57.077

58.542

58.851

59.178

59.479

60.062

60.366

60.931

61.851

62.116

62.434

62.622

62.646

63.702

64.598

65.122

67.979

70.497

73.125

75.292

The questionable fCO2A_uATM data for the following year days (JD) were

removed (initialized to --999.99):

JD

57.678

57.681

57.684

57.687

57.699

57.702

57.705

57.708

67.595

67.598

67.601

67.604

67.616

67.619

67.622

67.625