Brief Cruise Summary


	The R/V Knorr departed from Recife, Brazil on the morning of April 3,1994.  The ship 
steamed  north following the coast up to 3 59.8 South, 37 27.4 West, where we began sampling on 
April 6th.  We then went north-east on a short section to 2 20.2 S, 35 57.1 W (stations 1-8), then 
directly north over the Parnaiba Ridge, then the equator to 1 35.0 N 35 56.9 W (stations 8-22).  
From there, we went east for 5 days to 7 30.0 N, 18.59.9 W (station 28).  No CTD samples were 
taken on stations 23-27.  We then headed due South for 21 days, until we reached 32 S 19 W 
(stations 28-109).  During this section, we crossed the equator again, the Romanche Fracture Zone 
(station 45), the Chain Fracture Zone (station 49) and the Meteor Intercalibration station (station 
68).  We then retraced our path to 18 36.8 S, 17 54.1 W.  We then headed due west for 11 days  to 
18 53.9 S, 37 51.3 W (stations 110-153), just south of Salvador. Finally we made the trip in to 
Salvador and arrived in port the morning of May 21st.  Stations were an average of 30 nm apart 
allowing 3 to 4 stations per day for a total of 152 stations (there was no station 10).  Samples were 
collected by a 36 bottle Niskin rosette. The ships supply of seawater from the bow to the pCO2 
system malfunctioned several times during the cruise.  Hence, underway CO2 partial pressure data 
was collected with some interruptions. Weather during the cruise was highly favorable.

Total Carbon Dioxide

	Total carbon dioxide was measured by a coulometric system similar to that of Ken 
Johnson et al. (1985).  Our system consists of five elements: a printer, a computer, a Balston 
CO2-free air generator, a Dissolved Inorganic Carbon Extractor (DICE), and a coulometer.  The 
Balston takes the place of a nitrogen tank.  Using the gas delivered by the Balston, the computer 
instructs the DICE to automatically rinse its own sample lines and pipette.  Then it fills the 
pipette.  The computer then monitors the coulometer for stability.  Once it is reached, the 
computer allows the DICE to inject the sample into the stripper. The sample is acidified (with 1 to 
1.5 ml of 8.5% phosphoric acid) and the carbon dioxide is extracted.  It is carried by a constant 
gas flow (called the carrier gas) to the coulometer cell.  This cell contains a mixture which 
includes monoethanolamine.  The incoming CO2 is captured by the monoethanolamine to 
produce hydroxyethylcarbamic acid.  The presence of this acid causes the thymolphthalein 
indicator to change in color from deep blue to clear.  The coulometer reads this change by 
detecting the rise in percent transmittance.  It then produces a base at the silver anode to 
neutralize the acid and return the solution to the starting transmittance.  The computer 
automates the entire operation.

	The calibration is accomplished by running six sodium carbonate standards (prepared in 
distilled water) in concentrations of 0, 500, 1000, 1500, 2000, and 2500 mM C/l (micromoles of 
carbon per liter). In order to prepare these standards, the sodium carbonate is heated to 285 o C 
for a minimum of two hours. The five salt vials are weighed out, then air buoyancy corrected.  
Each one liter volumetric is flushed with nitrogen before the standard is made.  Once run, these 
six standards will have produced a value of counts corresponding to each concentration which 
the computer will use to derive the slope.  The slope will be used to convert counts from the 
coulometer into mmol/kg of carbon.  This procedure has first been described by Goyet and 
Hacker (1992) and is included in the DOE handbook of methods for CO2  analysis (DOE 1994).

Total Alkalinity

	The total alkalinity was measured on a potentiometric titration system similar to that 
described by Brewer et al. (1986).  The system consists of  a printer, a computer, a Dosimat acid 
dispenser, a pH meter and a closed acrylic cell which includes an expansion plunger, an 
electrode, a thermometer, an acid injection port and a spin bar.  A seawater sample is loaded 
into the cell.  The Dosimat adds hydrochloric acid in 0.1 ml steps as the pH meter monitors the 
millivolt reading.  The computer monitors the millivolt signal and waits for stability until the next 
acid aliquot is added.  The computer uses a Gran function to accurately determine the acid 
volumes at the two inflection points.  These volumes are then used to calculate the total 
alkalinity and total carbon dioxide concentrations of the sample.

	The calibration procedure for the system requires it be calibrated every time a new one 
liter aliquot of acid is prepared.  The acid for the Dosimat is 0.1 normal hydrochloric acid in a 
sodium chloride solution prepared from a 0.1 N HCl Dilut-it ampoule (J.T. Baker). A one liter 
distilled water aliquot is normally made up.  The calibration procedure calculates the ratio of the 
acid concentration over the cell volume.  At least two standards are made up with distilled water, 
sodium carbonate and sodium chloride which produce a solution with a salinity of 35 and a total 
alkalinity of 2280 umol/kg. Two standards must give the same cell volume (within +  0.1 ml) for 
the calibration to be completed.