Sulphate Reduction in Surface Sediments of the South-East Atlantic Continental Margin (Benguela Upwelling)

Abstract

The benthic remineralization of organic carbon exerts an important influence on the flux and distribution of carbon and nutrients throughout the ocean especially along continental margins. The distribution of oxygen, the fluxes of dissolved inorganic carbon, dissolved organic carbon ,and nutrients as well as the balance between water column particulate organic carbon flux and the burial of organic carbon in the sediments is determined by the rate and pathway of organic carbon remineralization. In the deep ocean beyond the continental margins, 02 fluxes account for the sum total of benthic remineralization (Jahnke, 1996; Cai and Reimers, 1995). However, anaerobic processes begin to play a quantitatively important role in organic carbon remineralization in continental margin sediments, where organic matter is buried or becomes mixed beyond the zone where dissolved oxygen is present through diffusion or bioirrigation. Jahnke (1996) has suggested that continental margin sediments within the deep ocean (sediments > 1000 m water depth) remineralize approximately 40% of the particulate organic carbon flux to the deep ocean; anaerobic remineralization of organic carbon in these continental margin sediments may, thus, have a significant impact on the fluxes of carbon and associated nutrient elements on the deep ocean. The oxidation of organic carbon by dissimilatory sulphate reducing bacteria is thought to be the principal terminal process of anaerobic respiration in continental margin sediments (Jorgensen, 1982; Canfield et al., 1993, Thamdrup and Canfield, 1996). Fortunately, and in contrast to the measurement of most other respiratory processes in marine sediments, a robust and relatively simple method for the determination of dissimilatory sulphate reduction Max-Planck-Institute for Marine Microbiology, Celsiusstr. 1, D-28359 Bremen, Germany