Sediment provenance shifts in the South Yellow Sea: Implications of reduced river discharges over the past 60 years

Abstract

The Yellow River and Yangtze River significantly influence the South Yellow Sea (SYS) through sediment discharges. Over the past several decades, sediment loads from these rivers into the sea have dramatically decreased due to climate change and intensified human activities. However, there is limited understanding of how this reduction in river discharge might affect the provenance of sediments in the SYS. To address this, surface sediment samples were collected at identical stations in the SYS during two periods: 1958 and 2012. Grain size analysis revealed notable differences: in 2012, clay content decreased, and silt increased, resulting in coarser sediments compared to 1958. Provenance analysis revealed that the fine-grained surface sediments in the SYS were primarily derived from the Yellow and Yangtze Rivers, as evidenced by clay mineral compositions (illite, smectite, kaolinite, and chlorite) and element ratios (Ti/Al vs. Ti/Zr, and Ti/Zr vs. La/Hf). Interestingly, despite reduced sediment loads, the influence of the Yellow River expanded, while the influence of the Yangtze River decreased between 1958 and 2012. These changes in provenance are attributed to differences in sediment transport mechanisms from each source to the SYS. Reduced Yangtze sediment load led to decreased deposition off the Jiangsu coast during summer, limiting Yangtze-derived sediments in the SYS during winter. Conversely, resuspended sediments from the modern and old Yellow River subaqueous deltas provided continuous supply of material to the SYS. This study provides valuable insights into source-to-sink processes in marginal seas, particularly as global rivers continue to experience reductions in sediment discharge.