Yangtze River-derived sediments in the southwestern South Yellow Sea: Provenance discrimination and seasonal transport mechanisms

Abstract

The southwestern South Yellow Sea (SYS) is influenced by tremendous sediment loads derived from the Yellow River (Huanghe) and the Yangtze River (Changjiang). However, the influence of Yangtze River sediments and their transport mechanism in this area remain unresolved. In this study, we present the grain size, clay minerals, and elemental compositions of surface sediments from the southwestern SYS, together with an analysis of field observation seawater salinity and suspended sediment data, to investigate the provenance and transport mechanism of the sediments. Discrimination diagrams of clay minerals, Cr/Th vs. Sc/Al, and rare earth elements (REEs) indicate that the southwestern SYS sediments are mainly derived from the old Yellow River subaqueous delta and the Yangtze River. Interestingly, Yangtze sediments enter the SYS in ways that differ seasonally. In summer, Yangtze sediments may be transported into the central SYS by the dispersion of Changjiang Diluted Water (CDW) and may also be transported northwestward by the Subei Coastal Current (SCC) to the area off the Jiangsu coast. In winter, the Yangtze-derived sediments deposited off the Jiangsu coast in summer are transported into the central and/or even north SYS under the combined effects of the SCC, Yellow Sea Coastal Current (YSCC), and Yellow Sea Warm Current (YSWC). Throughout the transport processes, there is an alternation between a source and sink of Yangtze sediments off the Jiangsu coast; the coast serves as a sink of Yangtze sediments in summer but as a source of SYS sedimentation in winter. The depositional and transport mechanisms of Yangtze-derived sediments are closely associated with seasonal variations in the circulation system of the SYS.