**M20707 Readme File**

**Principal Investigator/Organization:**

Dr. Richard Feely

NOAA/PMEL

7600 Sand Point Way NE

Seattle, WA 98115

\(206\) 526-6214

Richard.A.Feely@noaa.gov

**Ship Name:** McArthur II

Call Sign: WTEJ

Country: United States

Ship Owner: National Oceanic and Atmospheric Administration (NOAA)

**Temporal Coverage:**

Cruise Start: July 17, 2007; Port Angeles, WA

Cruise End: July 26, 2007; Seattle, WA

**System Operators:** Lacey O'Neil (Survey Tech)

**Dataset ID/Location:** M20707.csv (www.pmel.noaa.gov/co2/uwpco2/)

**Experiment Name:** Underway measurement of atmospheric and surface
water pCO2

**Geographical Bounds (+ E, - W for Longitude; + N, - S for Latitude):**

Westernmost Longitude: -126.346

Easternmost Longitude: -122.399

Northernmost Latitude: 46.758

Southernmost Latitude: 48.839

**Method Description:**

Equilibrator type/specifications: Showerhead, volume of \~0.5 L with a
headspace of \~ 0.8 L.

Water Flow rate: 3.5 L/minute

Headspace gas flow rate: 60 ml/minute

Measurement method: Infrared absorption of dried gas.

CO2 Sensor: Licor 6262, Serial \# IRG3-1242

Resolution/Uncertainty: 0.3 uatm for equilibrator measurements, 0.2 utam
for atmospheric measurements.

The general principle of instrumental design and operation are described
in:

Feely, R.A., R. Wanninkhof, H.B. Milburn, C.E. Cosca, M. Stapp, and P.P.
Murphy, A new automated underway system for making high precision pCO2
measurements onboard research ships, Analytica Chim. Acta, 377, 185-191,
1998.

and

Wanninkhof and Thoning, Measurement of fugacity of Carbon Dioxide in
surface water and air using continuous sampling methods, Marine
Chemistry, 44, 189-205, 1993.

**Standard gases:**

Standard gases are supplied by NOAA's Climate Monitoring Diagnostics
Laboratory in Boulder, CO, and are directly traceable to the WMO scale.
Any value outside the range of the standards should be considered
approximate, although the general trends should be indicative of the
seawater chemistry.

Serial numbers and CO2 concentrations for the cylinders used on this
cruise:

CA04403 299.45

CA06867 360.15

CC115011 493.18

CA05395 547.55

**Sampling Cycle**:

The system runs a full cycle in approximately 112 minutes. The cycle
starts with 4 standard gases, then measures 10 atmospheric samples
followed by 60 surface water samples. Each new gas is flushed through
the Licor Analyzer for 4 minutes prior to a 10 second reading from the
analyzer during which the sample cell is open to the atmosphere.
Subsequent samples of the same gas are flushed through the Licor
Analyzer for 30 seconds prior to a stop-flow measurement.

**Units:**

All xCO2 values are reported in parts per million by volume (ppmv) and
fCO2 values are reported in microatmospheres (uatm) assuming 100 %
humidity at the equilibrator temperature.

**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 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.

# File Format

**COLUMN HEADER DESCRIPTION**

1\. GROUP/SHIP: PMEL/McArthurII

2\. CRUISE_ID: M2\<Year\>\<nth cruise of year\>

3\. JD_GMT: Decimal year day

4\. Date_DDMMYYYY Date in the format DDMMYYYY

5\. TIME_HH:MM:SS: GMT HH:MM:SS

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 2m below the water
> line.

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

10 xCO2A_INTERPOLATED_PPM: xCO2atm_ppm averaged linearly to match up
with

> measurements xCO2eq_ppm

11 PRES_EQUIL_hPa: Barometric pressure in the equilibrator

12 PRES_SEALEVEL_hPa: Barometric pressure in the atmosphere

13\. EqTEMP_C: Temperature in the equilibrator water.

14\. SST(TSG)\_C: Temperature from the ship\'s bow intake.

15\. SAL(TSG)\_PERMIL: Thermosalinograph salinity

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

> microatmospheres calculated as outlined in the DOE Handbook.

17\. CO2A_uATM: Fugacity of CO2 in air in microatmospheres

18\. dfCO2_uatm: Sea water fCO2 - air fCO2 in microatmospheres.

19\. QC_FLAG: Quality control flag 2 = Good value

3 = Questionable value

4 = Bad value

20\. QC_SUBFLAG: Descriptive quality control flag used when a value

> receives a "3" QC flag
>
> 1 = Outside of Standard Range
>
> 2 = Questionable/interpolated SST
>
> 3 = Questionable EQU temperature
>
> 4 = Anomalous ΔT (EqT -- SST)( ± 1°C)
>
> 5 = Questionable Sea Surface Salinity
>
> 6 = Questionable pressure
>
> 7 = Low EQU gas flow
>
> 8 = Questionable air value
>
> 9= Interpolated standard value
>
> 10 = Other, see metadata

# References 

DOE (1994). Handbook of methods for the analysis of the various
parameters of the carbon

dioxide system in sea water; version 2. A.G. Dickson and C. Goyet, eds.,
ORNL/CDIAC-74.

Feely, R.A., R. Wanninkhof, H.B. Milburn, C.E. Cosca, M. Stapp, and P.P.
Murphy, A new automated underway system for making high precision pCO~2~
measurements onboard research ships, Analytica Chim. Acta, 377, 185-191,
1998.

Wanninkhof, R. and K. Thoning (1993) Measurement of fugacity of CO~2~ 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 CO~2~ in seawater. Nature 300:
511-513.

For questions or comments contact:

Cathy Cosca

NOAA/PMEL

7600 Sand Point Way NE

Seattle, WA 98115

206-526-6183

cathy.cosca@noaa.gov