Distribution and speciation of copper and its relationship with FDOM in the East China Sea

Abstract

Total dissolved Cu concentrations, concentrations and conditional stability constants of Cu-binding organic ligands, and the intensities of fluorescent dissolved organic matter (FDOM) components in seawater were determined in the East China Sea. Concentrations of organic ligands were determined using CLE-AdCSV with a 5 μM SA detection window. Total dissolved Cu concentrations ranged from 0.59 nM to 4.65 nM and were particularly high in surface waters with low salinity due to influences of the Changjiang Diluted Water. Concentrations of the stronger ligand (L1) were between 0.65 and 6.92 nM and its distribution closely followed that of dissolved Cu. Four FDOM components were detected in surface waters, including two humic-like and two protein-like components. L1 concentrations exhibited similar distribution patterns to the intensities of all four FDOM components. The concentrations of the weaker ligands (L2) ranged from 2.86 nM to 31 nM, with the highest concentrations detected in the surface waters of stations unaffected by the Kuroshio Current. We found the buffering ability of Cu-binding organic ligands in the East China Sea to be sufficient for responding to atmospheric and anthropogenic Cu inputs and keeping the free cupric ion concentrations relatively constant.