As part of the BMBF funded project TRAFFIC (Trophic Transfer Efficiency in the Benguela Current) and GENUS (Geochemistry and Ecology of the Namibian Upwelling System), the mole fraction of CO2 (xCO2) was measured in surface waters by using an underway pCO2 system (SUNDANS) during eight cruises. SUNDANS was developed by marine analytics and data (MARIANDA, Germany, www.marianda.com) according to the recommendations of the 2002 underway pCO2 system workshop in Miami. It was equipped with a shower type equilibrator, an open pre-equilibrator and a non-dispersive dual cell infrared gas analyzer (LI-7000). The LI-7000 was calibrated by using nitrogen gas (zero CO2) and a two additional standard gas for CO2. The standard gases were obtained from the company Deuste Steininger GmbH, Germany and revealed CO2 concentrations of 350 to 480 ppm (Std1) and around 800 ppm (Std2). The CO2 standard gases were calibrated against the standard gases provided by NOAA at the Institute for Baltic Sea Research in Warnemünde, Germany and the Leibniz Centre for Tropical Marine Research in Bremen, Germany. The xCO2 data were recorded each 6 seconds and subsequently averaged minute by minute. Minute by minute data on atmospheric pressure (Digital Barometer PTB220, Vaisala), wind speed (Ultrasonic Anemometer 2D, Thies), seawater temperature (Digital Oceanographic Thermometer SBE38, Sea-Bird Electronics, inc.) and salinity (Thermosalinograph SBE21 Seacat, Sea-Bird Electronics, inc.) were measured by underway systems mounted on board the research vessels (Data provided by the Federal Maritime and Hydrographic Agency, access under http://dship.bsh.de/). xCO2 was converted into pCO2 by using the CO2sys programme. The difference between the equilibrator and the sea water temperature was taken into account as suggested by Dickson et al. (2007, SOP5, page 8). Additional measurements on total alkalinity were carried out during SO285 using the VINDTA 2S system (MARIANDA, Germany, www.marianda.com). The samples were titrated with a fixed volume of hydrochloric acid (HCl) by equal increments of HCl (0.1 N HCl). The VINDATA 2S system was calibrated using Certified Reference Material provided by A. Dickson (Scripps Institution of Oceanography, La Jolla, CA, USA).