Late Quaternary evolution of the Yellow/East China Sea tidal regime and its impacts on sediments dispersal and seafloor morphology

The evolution of a tidal-current field in the Yellow Sea and East China Sea (YECS) in response to the sea-level rise since the last glacial maximum (LGM) was investigated using a two-dimensional tidal model, with special attention to changes in the sedimentary environment of the continental shelf region. It was found that tidal currents on the YECS shelf have generally been semi-diurnal throughout the post glacial stages, with F-ratio (index of diurnal inequality) and S₂/M₂ ratio (index of spring-neap cycle) remaining similar to present. On the other hand, the spatial distribution of the tidal bottom stress associated with M₂ and M₄ tidal currents changed greatly during the transgression. As the sea level rose, two core regions showing high bottom-stress values migrated shoreward from Cheju Island toward the west coast of Korea, and along the retreat path of the paleo-Changjiang Estuary. Distribution of 'extremely intense' tidal bottom stress suggested that intense tidal reworking may have occurred at sea levels from -90 to -45 m in the southeast Yellow Sea and at -75 to -60 m off the paleo-Changjiang Estuary, the latter of which agreed with the timing of a large terrigenous organic C flux observed on the shelf slope. Distribution of slightly weaker bottom stress indicated that the sand ridges off the Changjiang Estuary and in the southeast Yellow Sea also might have formed at during those periods. On the other hand, when the sea level was between -45 and-15 m, the tidal bottom stress was generally not strong enough to invoke significant reworking, even though the stress intensity may be stronger than present. Correlation with modern and relict sedimentary features suggested that the tidal process have played a significant role on the reworking and deposition of sediments on the YECS shelf.