DIFFUSIVE AND TOTAL OXYGEN-UPTAKE OF DEEP-SEA SEDIMENTS IN THE EASTERN SOUTH-ATLANTIC OCEAN - IN-SITU AND LABORATORY MEASUREMENTS

Total O-2 uptake rates were measured by the benthic flux chamber lander ELINOR, and O-2 microprofiles were measured by the profiling lander PROFILUR in the eastern South Atlantic. Diffusive O-2 fluxes through the diffusive boundary layer and the depth distribution of O-2 consumption rates within the sediment were calculated from the obtained microprofiles. The depth integrated O-2 consumption rate agreed closely with the diffusive O-2 uptake at all stations. Total O-2 uptake was 1.2-4.2 times the diffusive O-2 uptake, and the difference correlated with the abundance of macrofauna in the sediment. Diffusive O-2 uptake and O-2-penetration depths correlated with the organic content of the sediments and exhibited an inverse correlation with water depth. Total and diffusive rates of the in situ O-2 uptake were higher than previously published data for shelf and abyssal sediments in the Atlantic, but were comparable to rates from upwelling areas in the eastern Pacific. Laboratory measurements on recovered sediment cores showed lower O-2 penetration depths and higher diffusive uptake rates than in situ measurements. The differences increased with increasing water depth. We primarily ascribe this compression of O-2 profiles to a transiently increased temperature during recovery and enhanced microbial activity in decompressed sediment cores. Total O-2 uptake rates measured in the laboratory on macrofauna-rich stations were, in contrast, lower than those measured in situ because of underrepresentation and disturbance of the macrofauna.