1533 / 2024-09-27 21:42:05

Extreme erosion in the Changjiang subaqueous delta caused by intensification of storms during the Medieval Warm Period

Changjiang subaqueous delta,erosion,subbottom profile,paleo-strom

Session 53 - Geological analogues for future warm ocean and climate

River deltas play a crucial role in coastal zones. However, with the increase in human activities, accelerated sea level rise, and extreme weather events, the world's major river deltas are increasingly threatened by erosion and degradation. As one of the most densely populated areas in China, the Changjiang Delta has undergone erosion and siltation transformation in recent decades, with an increased risk of erosion. Among them, the erosion of subaqueous deltas has received a lot of attention. The existing studies mostly focus on the erosion of modern (tidal to decadal scale) process, but there is a lack of systematic understanding of erosion processes over longer time scales, especially in the deltaic progradation evolution cycle. Furthermore, the stratigraphic expression of erosion processes at various time scales is still unclear. In this study, a large number of high-resolution sub-bottom profiles and core data, combined with historical records, are used to attempt to discuss and quantify the response of the Changjiang subaqueous delta to paleo-storm events. Our analysis reveals that the Changjiang subaqueous delta has an obvious depositional discontinuity at ~0.8-1.4 ka BP, which occurs at burial depths ranging from ~20 m to ~30 m while extending deeper toward offshore areas until it pinches out around 30 m depth. At the same time, the accumulation of shell layers in several cores during this period indicates a storm-led erosion process, which may reach ~ 5500 km². While many paleoclimatic records show that the frequency of stroms in the eastern shelf of China and its adjacent areas increased significantly during the Medieval Warm Period, which provided strong hydrodynamic conditions for the occurrence of erosion. At the same time, the Changjiang basin has experienced aridity, which has also led to a reduction in sediment recharge in the estuarine area, thereby intensifying erosion. In light of current global warming and the doubling of storm intensity indices over nearly 40 years, river deltas that are already deficient in sediment recharge will confront increasingly severe erosion challenges. This study provides valuable insights into the erosion processes affecting the delta within the context of climate change, and it is crucial not to overlook the potential impacts of extreme weather on these deltas in the future.