Transport Patterns of Seasonal Suspended Particulate Matter Around the Western Sunda Shelf

The transport of suspended particulate matter is a crucial aspect of studies on sediment source-to-sink processes. However, research on its transport patterns in high-erosion areas of low-latitude seas remains limited. To elucidate modern land-sea interaction processes controlled by the monsoon climate, this study investigates the seasonal transport patterns and control mechanisms of suspended particulate matter in the western Sunda Shelf. Results reveal significant seasonal variations in the spatial distribution of suspended particulate matter concentrations, with elevated levels observed during autumn compared with spring. These differences are directly attributed to the East Asian monsoon, including seasonal monsoon precipitation and the associated transport dynamics. During the northeast monsoon, the Malay Peninsula serves as a primary source for the western sea area, with terrestrial materials from its rivers transported to the northern Gulf of Thailand. This transport pattern shifts to an S-shaped, clockwise circulation during upwelling events. Conversely, in the southwest monsoon, rivers in the northern Gulf of Thailand become the predominant sources for the Sunda Shelf, with terrestrial materials carried by clockwise currents toward the eastern Malay Peninsula. When upwelling occurs off the southern Indochina Peninsula, one branch heads toward the South China Sea and the other toward the southern tip of the Malay Peninsula. The seasonal variation in material sources is further supported by the distribution of clay minerals and the discrimination results of rare earth element proxies, including (La/Sm)_UCC-(Gd/Yb)_UCC and (La/Yb)_UCC-(Gd/Yb)_UCC, in surface sediments from the Sunda Shelf and surrounding marine areas.