The South China Sea (SCS) is the largest marginal sea in the western Pacific and comprises an ideal natural laboratory for studying deep-sea processes. Previous investigations in the region have primarily focused on surface currents and to a lesser extent on intermediate currents, while observations of bottom currents are scarce, hindering our understanding of deep ocean sediment transport and deposition mechanisms. Here, we carried out grain size measurement and end-member modelling analysis (EMMA) on samples collected by a sediment trap at a water depth of 1500 m in the Xisha Trough in the northwestern South China Sea. Grain size data shows that terrigenous material has particle sizes ranging from 0.3 μm to 745.9 μm and a peak at 4–11 μm. The EMMA result suggests that finer sediment accounting for an average of 48.2% of the sediment represents material transported by deep water currents (End-member 1; EM1), and this is primary sediment source in the region. Coarser sediment contributing to 32.9% of the sediment is the second most significant source (EM3), representing the deposits of surface currents influenced by monsoons and deposited close to the source. A third sediment type (EM2) constituting approximately 18.9% of the sediment exhibits a wide range of grain sizes and rapid changes, indicating transport in the bottom nepheloid layer triggered by anticyclonic eddies. Our study identifies three primary sediment transport mechanisms to the northwestern SCS, bridging present-day observations with paleoceanography and providing a crucial basis for future research on paleoceanographic reconstructions.

中文翻译：

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基于西沙海槽沉积物圈闭记录对南海西北部陆源沉积物供应的控制

南海（SCS）是西太平洋最大的边缘海，是研究深海过程的理想天然实验室。此前对该地区的研究主要集中在表层洋流，其次是中间洋流，而对底部洋流的观测很少，这阻碍了我们对深海沉积物输运和沉积机制的理解。在这里，我们对南海西北部西沙海槽水深1500 m的沉积物收集器采集的样品进行了粒度测量和端元模拟分析（EMMA）。粒度数据显示，陆源物质的粒度范围为 0.3 μm 至 745.9 μm，峰值在 4-11 μm。 EMMA结果表明，平均占沉积物总量48.2%的细沉积物代表了深水流输送的物质（端元1；EM1），这是该地区的主要沉积物来源。占沉积物总量 32.9% 的粗沉积物是第二重要来源 (EM3)，代表受季风影响并在源头附近沉积的地表水流沉积物。第三种沉积物类型（EM2）约占沉积物的18.9%，其颗粒尺寸范围广泛且变化迅速，表明底部霞云层由反气旋涡流引发的输送。我们的研究确定了南海西北部的三种主要沉积物输送机制，将当今的观测与古海洋学联系起来，并为未来的古海洋学重建研究提供了重要基础。