Rates of organic carbon oxidation in deep sea sediments in the eastern North Atlantic from pore water profiles of O_2 and the Delta~(13)C of dissolved inorganic carbon

摘要

The remineralization rate of sedimentary organic carbon (R+(org)) and the depth-integrated, diffusion-supplied O_2 consumption rate (IOC) during microbial metabolism in sediments was investigated in three deep-sea sites at 1100, 2000 and 3500 m water depth in the eastern north Atlantic during the spring and summer 1998. In-situ pore water O_2 profiles yielded an IOC of 0.45 + - 0.07 mmol O_2 m~(-2) day~(-1) at the deepest site (n=3) and ca. 1-1.5 mmol O_2 m~(-2) day~(-1) at the shallowest site (n=2). The Rare was independently estimated at all three sites from ex-situ pore water profiles of the isotopic composition of total dissolved inorganic carbon (delta~(13)Cr), assuming that the concentration and isotopic composition of pore water Cr with depth in the sediment was controlled only by microbial oxidation of isotopically depleted sedimentary organic carbon. The R_(org) was thus estimated to be ca. 0.5-0.6 mmol C m~(-2) day~(-1) at the shallowest site and ca. 0.3-0.4 mmol C m~(-2) day~(-1) at the two deeper sites. Stoichiometric and isotopic constraints indicated that oxic remineralization of sedimentary organic matter was the dominant metabolic pathway in the sediments at 3500 m water depth. Similarly, Stoichiometric and isotopic constraints suggested that the R_(org) estimates from the ex-situ pore water delta~(13)Cr profiles from 1100 and 2000 m water depth were likely to be minimum values and provided evidence for the occurrence of post-oxic remineralization processes. Post-oxic metabolism in the sediments of these sites could be linked to, or even augmented by, the non-diffusive mode of supply of organic matter mediated by infaunal organisms below the oxic sediment layer.