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 ship’s 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.