1105 / 2024-09-20 12:50:30

Variations in water mass interaction and depositional dynamic effects outside the Yangtze Estuary since the Middle Holocene

Yangtze River underwater delta; Yangtze River diluted water; Yellow Sea coastal current; Kuroshio; Paleoclimate; Sedimentary dynamics

The interaction model of water mass outside the Yangtze River mouth plays an important role in sediment capture in the Yangtze River delta, which is the hub of sediment source and sink in the East China Sea. At present, we know little about the detailed interaction process, regulation mechanism and water barrier effect between Changjiang diluted water and continental shelf water mass in Holocene high sea level stage which is similar to modern tidal current field. In this paper, we compare the temporal and spatial patterns of water mass evolution recorded by foraminifera in Holocene high water system sediments from different locations outside the Yangtze River estuary since 7ka. The results show that before 2.3 ka, Yangtze River diluted water (YDW) mainly interacts with Yellow Sea coastal water (YSCC), and then mainly interacts with Taiwan Warm Current (TWC). The changes of YSCC, TWC and YDW foraminifera indicators indicate that the relative intensity changes between the Yellow Sea Cold water mass (YSCBW) and Kuroshio (KC) and the Yangtze River runoff under climate control regulate the interaction pattern of water mass outside the Yangtze River mouth. It is worth emphasizing that the strength and path of YSBW and YSCC play a crucial role in the water mass pattern and water barrier effect outside the Yangtze estuary. Strong YSCBW and YSCC at 7-5 ka suppressed the inshore invasion of TWC and controlled most of the bottom water outside the Yangtze River estuary, creating the dynamic mechanism of winter temperature front and summer cold water mass trapping sediment. With the weakening of 5-2ka YSCBW and the withdrawal of YSCC to the north, a transient high deposition rate occurred outside the Changjiang Estuary from early to late and from south to north for hundreds of years. Our findings provide a new perspective for the prediction of hydrodynamics and sedimentation trends outside the Yangtze estuary under future global warming and sea level rise scenarios.