ORGANIC-CARBON TURNOVER TIME IN DEEP-SEA BENTHOS
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The ratio of organic carbon supply to the deep-sea floor estimated with sediment traps to total benthic biomass (in terms of organic carbon concentration) was used to calculate "average" turnover or residence times for the benthic community over a broad depth interval in the western North Atlantic. Ratios indicate that the biomass carbon turns over on average time scales of months, with little predictable variation over the depth interval (70m to 5300m). Detrital organic carbon in sediments at the same stations turned over on scales of years to centuries. The shortest detrital carbon turnover was just over 8 years in a sandy continental shelf environment versus 609 years at 5.3km depth on the Hatteras Abyssal Plain. The turnover time estimates calculated with POC fluxes were assessed by comparing POC fluxes with estimates of total community respiration. At each location the POC flux rates were greater than the sediment oxygen demand flux rates (in mg Carbon m-2d-1), and the disparity was much greater in the deep sea than on the continental margin. We suggest that this difference is primarily the result of a decline in the quality of the organic compounds in the rain of sinking POC, rather than physiological responses to cold or pressure. This implies that caution must be used when interpreting the relationships between the total organic carbon fluxes measured with sediment traps at great depths and rates of metabolic processes. 1990.