Trace elements (Fe, Mn, Co, Cu, Cd, and Ni) in the East Sea (Japan Sea): Distributions, boundary inputs, and scavenging processes

Abstract

The distributions of trace elements (Fe, Mn, Co, Cu, Cd, and Ni) were measured, for the first time, in the entire East Sea (22 stations, n = 276, 0–3400 m), which is located in the region directly affected by East Asian monsoon and the downstream of Tsushima Current. In general, the distribution patterns of these trace elements were similar to those in the major oceans. However, relatively higher concentrations of trace elements, except for Ni, were observed in the surface layer due to the pronounced external inputs (atmospheric deposition and/or continental shelf input). In addition, we observed unusually high concentrations of Fe and Mn in the bottom layer of the Ulleung Basin, owing to large benthic inputs. These inputs seem to be associated with the significant production/dissolution of Fe and Mn in organic-rich sediments (> 2.5%) and the subsequent diffusion of dissolved organic matter (DOM)-complexed Fe and Mn into the overlying seawater. In this bottom layer, the concentrations of Fe and Mn approached 13 and 57 nmol kg−1, respectively, which are an order of magnitude higher than those in the oxic deep water of other major oceans. Based on the plots of trace elements against nutrients, the scavenging of Co in the deep East Sea is found to be particularly efficient relative to other major oceans. The concentrations of Co in the deep East Sea (2500–3400 m) are the lowest reported concentrations (2–8 pmol kg−1) compared with those from the same depths in the global oceans, while those in the surface layer are 2- and 5-fold higher than those in the North Pacific and North Atlantic Oceans, respectively. Thus, the distinct distribution patterns of trace elements in this sea reveal the efficient scavenging processes related to the high sinking fluxes of particles under the significant boundary input conditions (atmospheric deposition, continental shelf input, and benthic input). © 2021 The Authors