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 210Pb 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.

Oxygen isotopic fractionation during dissolved oxygen consumption in the bottom layer of the Ulleung Basin, East/Japan Sea

“…Therefore, the interaction between the bottom water and surface sediments should be considered a crucial factor affecting the distribution of DO in the study area. First, sediment resuspension that may be stimulated by near-bottom currents (Chang et al, 2009;Kim et al, 2013) and lateral transport (Lee et al, 2019) in the bottom layer of the UB can form the nepheloid layer and enable the reintroduction of deposited organic matter into the water column. Moreover, within the nepheloid layers, some evidence proves the behavior of reduced elements, such as dissolved Fe and Mn, released from sediments (e.g., Seo et al, 2022).…”

“…Compared with those of the other regions of the EJS, the surface sediments of the UB contain high organic carbon (>2.5% dry wt. ; Cha et al, 2007;Lee et al, 2008), which is unusually high considering its bed depth of 2200 m. There are several studies supporting the high organic matter content in the sediments of the UB; the high organic matter content could result from organic carbon accumulation rates exceeding 2 g C m -2 year -1 (Lee et al, 2008) associated with the combination of high export flux (f-ratio ≈ 0.28) of phytoplanktonderived labile organic carbon through enhanced primary production (Kwak et al, 2013) and lateral transport of resuspended organic matter that may be related to downslope currents along the continental slope (Yoo and Park, 2009;Hyun et al, 2017;Kim et al, 2017;Hahm et al, 2019;Lee et al, 2019;Hyun et al, 2022;. In general, the degradation of excess organic matter in bottom waters near sediments significantly influences DO concentrations and its d 18 O DO (Wassenaar and Hendry, 2007;Zhou et al, 2021).…”

Significant benthic fluxes of bioavailable dissolved amino acids to the ocean: Results from the East/Japan Sea

“…The sediment of the East Sea is characterized by high OM content (> 2.5% dry wt. ; Cha et al 2007), high OM mineralization rates (Lee et al 2008;Lee et al 2019), and high benthic microbial metabolic activity (Hyun et al 2017).…”