Description: Respiration rates of 16 calanoid copepod species from the northern Benguela upwelling system were measured on board RRS Discovery in September/October 2010 to determine their energy requirements and assess their significance in the carbon cycle. Individual respiration rates were standardised to a mean copepod body mass and a temperature regime typical of the northern Benguela Current. These adjusted respiration rates revealed two different activity levels (active and resting) in copepodids C5 of Calanoides carinatus and females of Rhincalanus nasutus, which reduced their metabolism during dormancy by 82% and 62%, respectively. An allometric function (Imax) and an energy budget approach were performed to calculate ingestion rates. Imax generally overestimated the ingestion rates derived from the energy budget approach by 〉75%. We suggest that the energy budget approach is the more reliable approximation with a total calanoid copepod (mainly females) consumption of 78 mg C m-2 d-1 in neritic regions and 21 mg C m-2 d-1 in oceanic regions. The two primarily herbivorous copepods C. carinatus (neritic) and Nannocalanus minor (oceanic) contributed 83% and 5%, respectively, to total consumption by calanoid copepods. Locally, C. carinatus can remove up to 90% of the diatom biomass daily. In contrast, the maximum daily removal of dinoflagellate biomass by N. minor was 9%. These estimates imply that C. carinatus is an important primary consumers in the neritic province of the northern Benguela system, while N. minor has little grazing impact on phytoplankton populations further offshore. Data on energy requirements and total consumption rates of dominant calanoid copepods of this study are essential for the development of realistic carbon budgets and food-web models for the northern Benguela upwelling system.

Description: Within the BMBF funded project 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) duirng seven 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 (Ref. No. CA07600 and CC311968) and the Centre for Tropical Marine Research in Bremen, Germany (Ref. No. CB08923 and CA06265). The xCO2 data were recorded each 6 seconds and subsequently averaged minute by minute. Minute by minute data on atmospheric pressure, wind speed, seawater temperature and salinity were measured by underway systems mounted on board the research vessels. xCO2 was converted into pCO2 by using the CO2 sys program. The difference between the equilibrator and the sea water temperature was taken into account as suggested by Dickson et al. (2007, SOP5, page 8). During the RV Metoer cruise M67/2 between May 15 and June 05 2008 the pCO was measured by using PSI CO2-ProTM underwater carbon dioxide sensor designs by Pro-Oceanus Systems In., USA.