Organic carbon oxidation and preservation in NW Atlantic continental margin sediments

Publisher Website
Google Scholar
Abstract
Summary: We present distributions of pore-water inorganic metabolites (nitrate, ammonia, manganese and iron), dissolved organic matter (DOM) including dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP) and solid-phase organic carbon from the Hatteras Abyssal Plain, the Hatteras Continental Rise and Slope and the northern Bermuda Rise areas of the eastern United States seaboard. Organic carbon oxidation rates in the sediments were calculated from models of the pore-water inorganic metabolites and the solid-phase organic carbon distributions. The pore-water model results were consistently higher than rates determined from the sediment organic carbon distribution. This result may reflect an inappropriate use of bulk sediment mixing coefficients in simple solid-phase models to estimate rates of interfacial diagenetic processes. The organic carbon oxidation rates in the sediments were combined with the organic carbon burial rates to assess the particulate organic flux into the sediments, and these results were compared with the particulate organic rain caught in sediment traps. Trap fluxes were consistently higher than model-estimated fluxes. We cannot make an unequivocal interpretation of the organic carbon mass balance, but we suggest that rates of benthic metabolism estimated from inorganic metabolite and sediment organic carbon distributions underestimate rates of organic carbon cycling because some fraction of the particulate organic carbon rain caught in traps is remineralized as DOM. Pore-water enrichments of DOM, DOC and DON were a factor of 5–10 higher than bottom-water concentrations, suggesting a flux of DOM to bottom waters. DOM fluxes to bottom waters contribute to abyssal metabolism in the benthic boundary layer and not to sediment metabolism.