Distribution and stoichiometry of Al, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb in the East China Sea

Abstract

The dissolved (d) and total dissolvable (td) trace metals were determined in seawater samples collected from the East China Sea (ECS). Labile particulate (lp) species was calculated as td minus d, and the sectional and vertical distributions of d and lp trace metals were evaluated. The surface concentrations of dAl, dCo, dNi, dCu, and dPb were higher in the continental shelf region than in the Kuroshio region. lpAl and lpFe were the dominant species below a depth of 400 m, and a strong positive correlation was observed between them in the Kuroshio region. The enrichment factor (EF) against crustal abundance was calculated for the purpose of estimating the origin of dMs in the ECS. The EF(dFe) was close to unity. These results suggest that both lpFe and dFe are dominated by crustal sources. The other elements had high EF, indicating significant contributions from other sources. EF(dPb) was close to the enrichment factor in aerosol, suggesting atmospheric input from anthropogenic sources. The dM/P ratios were calculated to investigate the validity of the extended Redfield ratio in the ECS. The Mn/P, Co/P, Cu/P, Zn/P, and Cd/P ratios in shallow water (< 200 m) were within the same order of magnitude as those in phytoplankton. In contrast, the Al/P and Fe/P ratios were, respectively, 27 and 213 times higher in phytoplankton compared to those in shallow water. These results suggest that dFe is a potential limiting factor for biological production, although it is not exhausted in surface water.