Isotopic evolution of dissolved Ni, Cu, and Zn along the Kuroshio through the East China Sea

Abstract

In this study, we have investigated the evolution of concentrations and isotope ratios of dissolved nickel (Ni), copper (Cu), and zinc (Zn) from the North Equatorial Current in the western North Pacific to the Kuroshio in the East China Sea, where the inputs of anthropogenic and lithogenic materials through riverine and aeolian pathways are relatively high. The concentrations and isotope ratios for Ni, Cu, and Zn in the deep water of the East China Sea are similar to those of the western North Pacific. The concentrations of Ni, Cu, and Zn in the Changjiang diluted water (<34.0 of salinity) are 3.0–4.1 nmol/kg, 2.0–2.7 nmol/kg, and 0.5–1.1 nmol/kg, respectively, which are significantly higher than those in the surface water of the western North Pacific, thereby indicating the impact of the riverine input. In the Changjiang diluted water, isotope ratios of Ni range from +0.8 to +1.4‰, which is lower than +1.7‰ observed in the surface water (<150 m) of the western North Pacific. The distribution of concentrations and isotope ratios for dissolved Ni fit with simple mixing among the three endmembers, Changjiang diluted water, Kuroshio surface water, and deep water in the western North Pacific. A mixing model using isotope ratios and concentrations for Ni quantitatively evaluates the sources of dissolved Ni in the East China Sea. The ranges of the isotope ratios are +0.4 to +0.5‰ for Cu and −0.1 to +0.2‰ for Zn in the Changjiang diluted water, which are similar to those in the surface water of the Okinawa Trough but lower than those in the distal ocean, such as the central Pacific. Compared with published data from the global ocean, dissolved Ni, Cu, and Zn are isotopically lighter in the surface water of some coastal regions than in the pelagic regions, indicating that isotopically light Ni, Cu, and Zn are supplied from the continents.