Total dissolved inorganic carbon (TCO2)
   	 The TCO2 concentration of seawater samples was determined by using the 
coulometric titration system (UIC Inc., Model 5011) described by Johnson et al. 
(1985, 1987).  The standards used were Na2CO3 in a matrix of 0.7M KCl, and were 
analyzed daily.
	The batch of CRMs (Dr. Andrew Dickson, SIO) that was shipped for our 
cruise was not stable and we were not able to use them as reference materials. 
Batch 1 CRMs had been used on a previous cruise by our group.  We were therefore 
able to reference our cruise data to Batch 1 CRMs by means of a non-certified 
seawater standard that had been collected on both cruises which gave similar 
results. Batch 1 CRM shipboard measurements yielded a mean value of 
2017.0 +/- 2.5 umol/kg (n=25), which compares with 2020.2 +/- 0.8 umol/kg (n=12) 
certified by SIO.  Data reported for this cruise have been corrected to the 
Batch 1 CRM value by adding the difference between the certified value and the 
mean shipboard CRM value (certified value - shipboard analyses).  Seawater 
samples for TCO2 analysis were drawn from the NiskinTM-type samplers into 
500mL borosilicate glass bottles and poisoned with 100uL of HgCl2. The samples 
were sealed with ground-glass stoppers coated with Type M Apiezon grease, and 
stored in a cooled environment before analysis (usually within 12 hours after 
collection).  The sample was introduced into a calibrated, thermostated (25C) 
pipette (~50mL), and then transferred to the extraction vessel and acidified 
with 4.5 ml of 10% phosphoric acid (previously stripped of CO2). The evolved 
CO2 gas passed through an Orbo-53 tube to remove volatile acids other than CO2 
and then into the titration cell of the coulometer by the N2 carrier gas.  
In the coulometric analysis of TCO2, all carbonate species are converted to 
CO2 (g) by addition of excess hydrogen to the seawater sample.  The evolved 
CO2 gas is carried into the titration cell of the coulometer, where it reacts 
quantitatively with a proprietary reagent based on ethanolamine to generate 
hydrogen ions.  These are subsequently titrated with coulometrically generated 
OH-. CO2 is thus measured by integrating the total charge required to achieve 
this.  The entire sequence takes between 8 to 11 minutes. All reagents in the 
extraction/analytical system were renewed daily.


 pH
 Sample cells (10-cm pathlength spectrophotometric cells, 30-cm3 volume) were 
filled directly from the NiskinTM-type bottle using a 20-cm length of silicone 
tubing. A flushing volume of approximately 300 mL was used. Care was taken to 
eliminate bubbles from the sampling system, and the sample cell was sealed with 
PTFE caps while ensuring that there was no head space.  All spectrophotometric 
pH measurements were made using the indicator m-Cresol Purple. Spectrophotometric 
cells were warmed to 25CC  within the water bath of a refrigerated thermocirculator. 
Subsequently cells were cleaned and placed in the thermostated sample compartment 
of the spectrophotometer. Absorbance measurements were made at three wavelengths: 
a non-absorbing wavelength (730 nm) and wavelengths corresponding to the absorbance 
maxima of the alkaline (I2-, 578 nm) and acidic (HI-, 434 nm) forms of the indicator. 
Subsequently, one of the cell caps was removed and 0.08 cm3 of concentrated indicator 
(2 umol/cm3) was injected into the cell. The cell was capped, rapidly mixed and 
returned to the thermostated cell. Absorbance measurements were again made at 
730 nm, 578 nm and 434 nm. Sample pH was then calculated using the equations 
and procedures of Clayton and Byrne (1993). The "total" pH scale is used, and 
pHT is reported in mol/kg of seawater.

Clayton T. and Byrne, R. H., 1993. Spectrophotometric seawater pH measurements: total 
hydrogen ion concentration scale calibration of m-cresol purple and at-sea results., 
Deep Sea Res., 40, 2115-2129.

Johnson, K.M., A.E. King, and J. McN. Sieburth (1985): Coulometric DIC analyses for 
marine studies: An introduction. Mar. Chem., 16, 61-82.

Johnson, K.M., P.J. Williams, L. Brandstrom, and J. McN. Sieburth (1987): Coulometric 
total carbon analysis for marine studies: Automation and calibration. Mar. Chem., 21, 117-133.