***Discrete measurements (TCO2, TALK, pCO2, and pH) metadata form***

*( \* = mandatory field)*

*Investigator:\**

*Name:\** Rik Wanninkhof

*Organization:* NOAA/AOML

*Address:* 4301 Rickenbacker Causeway

Miami FL 33149

*Phone:* 305-361-4379

*Email:* rik.wanninkhof@noaa.gov

*Dataset Info:\**

*Dataset ID:\** P16N_2006 discrete pCO2

*Submission Dates:\**

*Initial Submission: (yyyy/mm/dd): 5/5/06*

*Revised Submission: (yyyy/mm/dd)*

*Cruise Info:\**

*Experiment:* CLIVAR/CO2 repeat hydrography cruises

*Experiment Name:\** P16N_2006

*Cruise:*

*Cruise ID: (Expocode)* 3250TT191

*Section: (Leg)* leg 1 and leg 2

*Geographical Coverage:\**

*Geographical Region:* Central and North Pacific between Papeete, Tahiti
and Kodiak, Alaska

*Bounds:\**

*Westernmost Longitude:* 153 W

*Enter decimal fractions of degrees: (+ = E, - = W)*

*or Degrees, Minutes, Seconds: East West*

*Easternmost Longitude:* 150 W

*Enter decimal fractions of degrees: (+ = E, - = W)*

*or Degrees, Minutes, Seconds: East West*

*Northernmost Latitude:* 56 N

*Enter decimal fractions of degrees: (+ = N, - = S)*

*or Degrees, Minutes, Seconds: North South*

*Southernmost Latitude:* 17 S

*Enter decimal fractions of degrees: (+ = N, - = S)*

*or Degrees, Minutes, Seconds: North South*

*Temporal Coverage:*

*Start Date: (yyyy/mm/dd):* 2006/02/14

*End Date: (yyyy/mm/dd):* 2006/03/30

*Ports of Call: (One per line)*

Papeete, Tahiti

Honolulu, HI

Kodiak, AL

*Vessel:\**

*Vessel Name:* Thomas Thompson

*Vessel ID:*

*Country:*

*Vessel Owner:*

*Variables Info:\**

*Variable:* discrete pCO2 analyzed at constant temperature

*Variable Name:\** PCO2_UATM@20

*Description of Variable: (units)* : uatm

*Total Variables in the Data Set:*

*Method Description:\**

*pCO2 Data:*

*Analysis:*

*pCO2 Analysis Method:*

*Sample Volume: (mL)* 500 ml

*Headspace Volume:* 70 ml

*Measurement Temperature:* 20 or 12 C

*Temperature Normalization* 20 C

*Temperature Correction Method:* See Peng et al., 1987

*Variable Reported:*

*EXPOCODE:* identifier

*SECT_ID:* identifier

*STNNBR;* identifier

*CASTNO:* identifier

*SAMPNO:* identifier

*BTLNBR:* identifier

*BTLNBR_FLAG_W:* identifier

*DATE:* identifier

*TIME_GMT:* identifier

*LATITUDE:* identifier

*LONGITUDE:* identifier

*PCO2_UATM@T:* pCO2 at analysis temperature (See Peng et al., 1987)

*pCO2temp:* analysis temperature

*PCO2_20_UATM: pCO2 corrected to 20 C*

*PCO2_FLAG_W: QC flag (WOCE protocol )*

*Gas:*

*Standard Gas Concentrations:*

The cylinder serial numbers and mole fractions of CO~2~ with balance
artificial air are:

CA5998 205.1 ppm

CA5989 378.7 ppm

CA5988 593.6 ppm

CA5980 792.5 ppm

CA5984 1037.0 ppm

CA5940 1533.7 ppm

*Frequency of Standardization:*

In order to maintain analytical accuracy, a set of six gas standards is
run through the analyzer before and after every ten seawater samples.

*Field Replicate Info:*

Generally when samples were taken, flasks were drawn on all the Niskins
including four duplicates. Two of the duplicates were analyzed at
different temperatures

*Storage Method:*

Samples were drawn from Niskin bottles into 500 ml volumetric flasks
using Tygon© tubing with a Silicone adapter that fit over the petcock to
avoid contamination of DOM samples. Bottles were rinsed while inverted
and filled from the bottom, overflowing half a volume while taking care
not to entrain any bubbles. About 5 ml of water was withdrawn to allow
for expansion of the water as it warms and to provide space for the
stopper, tubing, and frit of the analytical system. Saturated mercuric
chloride solution (0.2 ml) was added as a preservative. The sample
bottles were sealed with a screw cap containing a polyethylene liner.
The samples were stored in coolers at room temperature generally for no
more than 5 hours.

*Accuracy Info: (Estimate overall precision and accuracy, and why)*

Three types of duplicates were taken. The average difference:
\[ABS(sample 1-sample2)/(sample 1+sample 2) \* 100\], std. dev. and
number for the three types are listed below:

Duplicates run at 20 C: av. dif. =0.3 +- 0.23% n = 33 (one value
omitted)

Duplicates run at 12 C: av. dif. = 0.3 +- 0.18 % n= 23 (one value
omitted)

Duplicates run at 12 C and 20 C\* av. dif = 0.7 +- 0.75 % n= 59 (two
values omitted)

The omitted values were because of a problem in analysis in one of the
duplicates

\*The duplicates run at different temperatures were normalized to 20 C
and compared. Normalization was performed using the constants and
procedures as outlined in Peng et al. 1987 as incorporated in the GW
BASIC data reduction program.

Of note is that using the constants as refit by Dickson and Millero and
the salinity dependence of borate as proposed by Dickson gave an average
difference of 1 %, that is, these constants yielded worse agreement in
temperature normalization.

*Method References: (Publication(s) describing method):*

Wanninkhof, R., and Thoning, K., 1993, Measurement of fugacity of CO~2~
in surface water using continuous and discrete sampling methods: Mar.
Chem., v. 44, no. 2-4, p. 189-205.

Chen, H., Wanninkhof, R., Feely, R. A., and Greeley, D., 1995,
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, ERL AOML-85.

Peng, T.-H., Takahashi, T., Broecker, W. S., and Olafsson, J., 1987,
Seasonal variability of carbon dioxide, nutrients and oxygen in the
northern North Atlantic surface water: observations and a model: Tellus,
v. 39B, p. 439-458.

*Additional information:*

The discrete pCO~2~ system is patterned after the instrument described
in Chipman et al. (1993) and is discussed in detail in Wanninkhof and
Thoning (1993) and Chen et al. (1995). The major difference between the
two systems is that Wanninkhof instrument uses a LI-COR© (model 6262)
non-dispersive infrared analyzer, while the Chipman instrument utilizes
a gas chromatograph with a flame ionization detector.

Once the samples reach the analyses temperature, a 50-ml headspace is
created by displacing the water using a compressed standard gas with a
CO~2~ mixing ratio close to the anticipated pCO~2~ of the water. The
headspace is circulated in a closed loop through the infrared analyzer
that measures CO~2~ and water vapor levels in the sample cell. The
samples are equilibrated until the running mean of 20 consecutive
1-second readings from the analyzer differ by less than 0.1 ppm (parts
per million by volume). This equilibration takes about 10 minutes. An
expandable volume in the circulation loop near the flask consisting of a
small, deflated balloon keeps the headspace of the flask at room
pressure.

In order to maintain analytical accuracy, a set of six gas standards is
run through the analyzer before and after every ten seawater samples.
The standards were obtained from Scott-Marin and referenced against
primary standards purchased from C.D. Keeling in 1991, which are on the
WMO-78 scale.

The calculation of pCO~2~ in water from the headspace measurement
involves several steps. The CO~2~ concentrations in the headspace are
determined via a second-degree polynomial fit using the nearest three
standard concentrations. Corrections for the water vapor concentration,
the barometric pressure, and the changes induced in the carbonate
equilibrium by the headspace-water mass transfer are made. The corrected
results are reported at the analytical temperature and at a reference
temperature of 20°C.

No instrumental problems occurred during the cruise. The relatively
time-consuming analyses and the presence of only one analyst limited the
spatial coverage. Sampling and analyses focused on precision and
accuracy rather than high throughput.

*Data Set References: (Publication(s) describing data set)*

*Citation: (How to cite this data set)*

*Data Set Link:*

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