Tracing the Changjiang-derived sediments along the southeast coast of China during the Holocene

Coastal processes, including riverine inputs, alongshore currents, tidal currents, and estuarine circulation, are crucial in shaping the Earth's landscape and regulating land-ocean material cycling. The Changjiang (Yangtze River), the largest river in Asia, has greatly influenced coastal sedimentation and environmental evolution in the East China Sea during the Holocene. However, its interactions with smaller mountainous rivers and their estuaries in southeastern China, as well as the impact of post-glacial sea-level rise on sediment source-to-sink dynamics in this region, remain poorly constrained. Here, we present a comprehensive analysis of the sedimentary characteristics, elemental composition, and SrNd isotopic ratios of Core MLX-S obtained from the Mulanxi River estuary. By comparing these findings with literature data from the Changjiang and other coastal estuaries in SE China, we provide new insights into the source-to-sink dynamics in this region. Our results indicate that the postglacial maximum flooding event occurred at ∼4.8 kyr BP in the southern Taiwan Strait and at ∼7.0 kyr BP in the northern Taiwan Strait. The terrigenous sediment mixing between the Changjiang and coastal mountainous rivers can be traced back to the early Holocene, coinciding with the postglacial sea levels rise. As the depositional environment shifted from low-stand fluvial to inner shelf settings, sediment provenances also changed from the dominance of local source (e.g., Mulanxi) to a mixture of sediments from the Changjiang and local rivers. The average proportion of Changjiang-sourced sediments in Core MLX-S was about 14.2 % during early Holocene (before 9.5 kyr BP), 25.0 % during the early-middle Holocene accompanied by rising sea level (9.5–7.7 kyr BP), 38.5 % during high sea-level period (7.7–0.3 kyr BP), and 29.9 % during the late Holocene with present sea level (after 0.3 kyr BP). These findings suggest that the initial influence of Changjiang sediments on the estuaries of the southeastern coastal rivers occurred prior to the formation of a large-scale mud belt on the inner shelf at ∼8.0 kyr BP. This study underscores the sensitivity of coastal sediment routing to sea-level and climate forcings, demonstrating how large river systems interact with regional smaller rivers to shape marginal marine stratigraphy.