Organic carbon fluxes, degradation, and accumulation in an anoxic basin: Sediment trap results from the Cariaco

Organic carbon fluxes were measured in the anoxic water column of the Cariaco Basin under varying levels of primary productivity. Our results indicate that water column degradation of fresh organic matter in this anoxic setting is similar to what has been previously observed in the open ocean. Additionally, the rate at which carbon is consumed increases as primary productivity increases. These findings support the hypothesis that sulfate reduction is as efficient as aerobic respiration in degrading labile organic matter and that an anoxic water column does not necessarily result in an enhanced delivery of organic carbon to the sea floor. We estimate that 1–2 % of the organic carbon produced at the surface reaches the seafloor and that approximately 50 % of this is preserved in the sediments. This burial efficiency is comparable to that previously reported for both oxic and anoxic settings, and with sedi-mentation rates similar to that in Cariaco Basin. Degradation and preservation rates of organic carbon in marine environments commonly are linked to oxygen avail-ability, with decomposition under aerobic conditions often considered to be more efficient than under anaerobic con-ditions (Toth and Lerman 1977; Reimers and Suess 1983