Dissolved copper in the Yellow Sea and the East China Sea - Cu as a tracer of the Changjiang discharge

The behavior of dissolved copper was investigated in the Yellow Sea in January (winter) and September (autumn) 1995, and in the East China Sea in February-March (winter) and October-November (autumn) 1993. Water sampling was carried out vertically on a transect on the PN line in the East China Sea, but only surface sampling was done in the Yellow Sea. The distribution of copper in the Yellow Sea showed an influence of variations in the Changjiang discharge; in September, when the discharge of the Changjiang was high and the river flowed northeastward, the surface copper concentration increased toward the Changjiang estuary, and a maximum value of 9.37 nM was found at the station nearest the river mouth. In the East China Sea, approximately 4 nM was observed near the Changjiang estuary in winter and autumn, and less than 1 nM was determined to be in the Kuroshio region in autumn. Plots of these copper concentrations against salinity data show a clear feature based on the mixing of water masses. In winter, the data were scattered around the Huanghe estuary (Bohai) line shown in Zhang (Coastral Shelf Sci 41 (1995) 631); in autumn, the points shifted in the direction of the Changjiang estuary line (Zhang, 1995), indicating an increased discharge and northeastward flow of the Changjiang in the summer-autumn period. Using three distinctly different copper-salinity end-members, it was determined that the contributions of the Changjiang water in autumn were 29.0% and 8.4% at the station nearest the Changjiang estuary in the Yellow Sea and the East China Sea surface water, respectively. On the other hand, in winter, the influence of Changjiang water was insignificant in the study area because the Changjiang outflow probably flowed southward and did not enter the study area. (C) 2002 Elsevier Science Ltd. All rights reserved.