Controls on the distributions of dissolved Cd, Cu, Zn, and Cu-binding organic ligands in the East China Sea
|Author(s)||Wong Kuo Hong1, 2, Obata Hajime1, Ikhsani Idha Yulia1, 3, Muhammad Ronald1|
|Affiliation(s)||1 : Atmosphere and Ocean Research Institute, The University of Tokyo
2 : College of Science and Engineering, Kanazawa University
3 : Research Center for Deep Sea, Indonesian Institute of Sciences
|Keyword(s)||Trace elements, geochemical cycles, organic ligand, water mixing, GEOTRACES, East China Sea|
The East China Sea (ECS) is a complex marginal sea with potential sources and sinks of trace metals. In this study, we investigated the distributions of dissolved Cd, Cu, Zn, and Cu-binding organic ligands in the ECS. Concentrations of Cd and macronutrients were below detection limit in the surface Kuroshio waters. Surface Zn concentrations increased along the Kuroshio Current, which may be attributed to atmospheric deposition. We detected two classes of Cu-binding organic ligands in those waters, classified as L1 (log K = 13.6-15.2) and L2 (log K = 11.2-13.1), respectively. L1 could be related to biological production while L2 distributions appeared to be controlled by water mass mixing. Particularly, the Kuroshio Surface Water had relatively low L2 concentrations. There were no significant sources of Cu-binding organic ligands in the intermediate waters. Cd, Cu, and Zn exhibited strong positive relationships with phosphate in the intermediate waters, suggesting that phytoplankton uptake and subsequent regeneration were the dominant controls of these elements at these depths. In deep waters, the distributions of Cd, Cu, and Zn were mainly controlled by water mass mixing. This was apparent from the unique trace metal to macronutrient ratios propagating from the South China Sea and West Philippine Sea to the ECS, according to water mass mixing patterns. Cd/phosphate, Zn/phosphate, Zn/silicate, and Cu/silicate ratios in the ECS were comparable with those in the North Pacific region. This implies the absence of additional supplies of Cd, Cu, Zn, and macronutrients from marginal sources in the ECS.