Carbon-related data measurements methods and instrumentation.
pH
	Seawater samples were drawn from the PVC bottles with a 25-cm length 
	of silicon tubing. One end of the tubing was fit over the petcock of 
	the PVC bottle and the other end was attached over the opening of a 
	10-cm glass spectrophotometric cell. The spectrophotometric cell was 
	rinsed three to four times with a total volume of approximately 200 mL 
	of seawater; the Teflon(tm) endcaps were also rinsed and then used to 
	trap a sample of seawater in the glass cell. While drawing the sample, 
	care was taken to make sure that no air bubbles were trapped within 
	the cell.
		
	Seawater pH was measured using a three-wavelength spectrophotometric 
	procedure (Byrne, 1987) and the indicator calibration of Clayton and 
	Byrne (1993). The indicator was a 8.0-mM solution of Kodak(tm) m-cresol 
	purple sodium salt (C21H17O5Na) in a 10% ethanol solution; the 
	absorbance ratio of the concentrated indicator solution (RI = 578A/434A) 
	was 1.00. All absorbance ratio measurements were obtained in the 
	thermostatted (25.0 +/- 0.05°C) cell compartments of HP 8453 diode array 
	spectrophotometers. Periodically the spectrophotometric cells were 
	cleaned with a 1 N HCl solution to preclude biological growth.  
	Measurements of pH were taken at 25.0C on the total hydrogen ion 
	concentration ([H+]t) scale, in mol/kg soln.

Total Carbon Dioxide (TCO2)

	The DIC analytical equipment was set up in a seagoing container 
	modified for use as a laboratory. The analysis was done by coulometry; 
	two analytical systems were used simultaneously on the cruise, each 
	consisting of a coulometer (UIC, Inc.) coupled with a SOMMA (Single 
	Operator Multiparameter Metabolic Analyzer) inlet system developed by 
	Ken Johnson (Johnson et al., 1985,1987,1993; Johnson, 1992) of Brookhaven 
	National Laboratory (BNL). Pipette volume was determined based on the 
	procedures described in Handbook of Methods for CO2 Analysis (DOE, 1994). 
	In the coulometric analysis of DIC, all carbonate species are converted 
	to CO2 (gas) by addition of excess hydrogen to the seawater sample, and 
	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.
	
	Samples were drawn from the PVC bottles into cleaned, precombusted 500-mL 
	Pyrex(tm) bottles using Tygon(tm) tubing according to procedures outlined 
	in the Handbook of Methods for CO2 Analysis (DOE, 1994). Bottles were 
	rinsed once and filled from the bottom, overflowing half a volume, and 
	care was taken not to entrain any bubbles. The tube was pinched off and 
	withdrawn, creating a 5-mL headspace, and 0.2 mL of saturated HgCl2 solution 
	was added as a preservative. The sample bottles were sealed with glass 
	stoppers lightly covered with Apiezon-L(tm) grease, and were stored at 
	room temperature for a maximum of 12 hours prior to analysis.
	The coulometers were calibrated by injecting aliquots of pure CO2 (99.995%) 
	by means of an 8-port valve outfitted with two sample loops that had been 
	calibrated at BNL (Wilke, 1993). All DIC values were corrected for dilution 
	by 0.2 mL of HgCl2; total water volume was 540 mL. The correction factor 
	used was 1.00037. The instruments were calibrated at the beginning, middle, 
	and end of each coulometer cell solution with a set of the gas loop injections.
	CRMs (Batch 29) were provided by Dr. Andrew Dickson (SIO), and was analyzed on 
	both instruments over the duration of the cruise.  The CRM certified value was 
	1902.54 +/-1.05 (n=14).  The overall accuracy and precision for the CRMs on both 
	instruments combined was -1.1 +/-0.9 (n=153).  Replicate measurements from 
	different PVC bottles tripped at the same depth, along with replicate measurements 
	from the same PVC bottle was within +/-1.9 µmol/kg DIC. DIC data reported for 
	this cruise have been corrected to the Batch 29 CRM value by adding the difference 
	between the certified value and the mean shipboard CRM value (certified 
	value - shipboard analyses) on a per instrument/per leg basis.   

Total Alkalinity (TA)

The titration system used to determine TA consisted of a Metrohm 665 Dosimat(tm) 
titrator and an Orion(tm) 720A pH meter controlled by a personal computer 
(Millero et al., 1993). The acid titrant, in a water-jacketed burette, and the 
seawater sample, in a water-jacketed cell, were kept at 25 +/- 0.1°C with a 
Neslab(tm) constant-temperature bath. The plexiglass water-jacketed cells were 
similar to those used by Bradshaw et al. (1988), except that a larger volume 
(200 mL) was used to increase the precision. The cells had fill and drain valves 
with zero dead-volume to increase the reproducibility of the cell volume. 

The HCl solutions used throughout the cruise were made, standardized, and stored 
in 500-mL glass bottles in the laboratory for use at sea. The 0.2487 M HCl solutions 
were made from 1 M Mallinckrodt(tm) standard solutions in 0.45 M NaCl to yield an 
ionic strength equivalent to that of average seawater (0.7 M). The acid was 
independently standardized using a coulometric technique (Taylor and Smith, 
1959; Marinenko and Taylor, 1968) by the University of Miami and by Dr. Dickson. 
The two standardization techniques agreed to +/-0.0001 N. 

The volume of HCl delivered to the cell is traditionally assumed to have a small 
uncertainty (Dickson, 1981) and is equated with the digital output of the titrator. 
Calibrations of the Dosimat(tm) burettes with Milli Q(tm) water at 25C indicated 
that the systems deliver 3.000 mL (the value for a titration of seawater) to a 
precision of 0.0004 mL. This uncertainty resulted in an error of 0.4 µmol/kg in TA. 
Internal consistency of each cell was checked before, during, and after the cruise 
by titrating CRM Batches 29 and 30 prepared by Dr. Dickson. The TA of CRM was 
determined by open cell (weighed) titration in the laboratory prior to the cruise 
and was found to be 2184.8 +/- 1.3 µmol/kg (n= 15) and 2201.9 +/- 1.0 µmol/kg 
(n = 21), respectively. A total of 85 CRM measurements made at sea yielded 
2173.8 +/- 1.6 µmol/kg for Batch 29 and 2190.8 +/- 1.7 µmol/kg for Batch 30 
on three different cells. This offset was due to changes in the volume of the 
cells. All TA data have been corrected to laboratory CRM values for each cell 
and each leg.