Hydrographic Measurements
Water samples were collected with a General Oceanics rosette equipped with twenty-four 10-L Niskin bottles mounted on a Neil Brown Mark III CTD instrument provided by the IfMK. For stations deeper than 3500 m, two separate CTD/rosette casts were launched. For stations with a depth less than 3500 m, one CTD/rosette cast of up to 24 bottles was lowered. Surface currents down to 300 m, surface temperature, and surface salinity were measured continuously during the cruise with a hull-mounted ADCP and a thermosalinograph. In between CTD stations, XBTs were routinely launched. Over the boundary currents, XBTs were launched every half hour, and over the Benguela Current, the XBT launches were supplemented with free-falling XCPs.
No serious problems were experienced with the CTD/rosette systems during the cruise. Repeated checks on board and several careful verifications using the complete bottle data sets have been carried out, and the sampling pressures have been assigned to each sample. Reversing thermometers of both the electronic (SIS, Kiel) and the mechanical (Gohla Precision, Kiel) types were also read at the completion of each cast. The processing and quality control of CTD and bottle data followed the published guidelines in the WOCE Operations Manual (WHPO 91-1, 1991).
The CTD pressure, temperature, and conductivity data were processed and corrected according to laboratory calibrations. Pressure values are expected to be accurate to ±3 dbar; temperature values to ±0.002°C. Salinity for selected Niskin bottles (about one in every three) was also determined on a Guildline Autosal model 8400A that was standardized weekly with International Association for the Physical Sciences of the Ocean (IAPSO) water. These data were also used to process the CTD data, and the final salinity data are expected to be accurate to ±0.002. Bottle oxygen was determined by Winkler titration after the technique of Carpenter (1965) with the modifications of Culberson et al. (1991), using standards and blanks run in seawater. The precision of the analyses determined from parallel analyses (n = 10) of samples at and well below saturation is ±0.4%. The concentrations of nitrate, nitrite, phosphate, and silicate dissolved in seawater were determined for samples collected in high-density polyethylene screw-capped bottles by a continuous-flow method with an autoanalyzer. Precision was as follows: silicate, ±1.3%; phosphate, ±1.5%; and nitrite/nitrate, ±1.1%. Preweighed standards were used to prepare the nutrient working standards aboard the ship.
