Sedimentary Organic Carbon Budget Across the Slope to the Basin in the Southwestern Ulleung (Tsushima) Basin of the East (Japan) Sea

Abstract

With the total sediment oxygen uptake rates measured using an in situ benthic chamber, vertical distributions of organic carbon, and sedimentation rates estimated by excess Pb-210 across the slope to the basin sediment of the southwestern region of the Ulleung (Tsushima) Basin (UB), the partitioning of organic carbon fluxes in the sediment was estimated to understand the biogeochemical cycles of organic carbon in the high productivity marginal sea. The results of depth attenuation of total oxygen uptake (TOU) demonstrate that the organic carbon oxidation of the UB sediment was 2.5 times higher than that obtained from the empirical relationship of the global's depth attenuation of TOU. Similar to TOU, the high mass accumulation rates observed in the slope region were 9.5 times higher than the rate in the basin, indicating that the slope may act as the depocenter of organic carbon. The organic carbon budget with water depth gradient implies that a significant fraction of the organic carbon deposited into sediment is supplied by lateral transport down the slope. Definite increasing C/N ratio with water depth indicates that the refractory organic carbon seems to be successively transported later from shelf to slope. The total burial flux in the sediment of southwestern UB was estimated to be 0.46 +/- 0.04 Tg C/year, which is similar to the megadepocenter of the Congo River fan. Our results imply that the UB sediment may be an important biogeochemical reaction place not only for organic carbon but also materials linked to primary production.