On the origin of the radial sand ridges in the southern Yellow Sea: Results from the modeling of the paleoradial tidal current fields off the Paleo-Yangtze River Estuary and northern Jiangsu coast

The origin of the radial sand ridges (RSR) in the southern Yellow Sea has been a controversial problem since they were discovered. The key to solving this problem is to answer whether the radial tidal current field existed prior to the formation of the RSR. With a two-dimensional tide model over the Bohai Sea, the Yellow Sea, and most of the East China Sea, the M₂ tides and tidal currents at around 7000 years BP, 6000 years BP, 3800 years BP, the 8th and 11th centuries AD are simulated. The model results show that, from 7000 years BP to 3800 years BP, tidal currents north of the major longitudinal axis of the Paleo-Yangtze River Estuary (PYRE) converged toward and diverged from the mouth of this river and the distribution pattern of the tidal current field was largely similar to that of the tidal current field over the southern Yellow Sea. Toward the 8th century AD, the PYRE became a delta. The Yangtze River mouth migrated southeastward considerably until the 11th century AD, and the shorelines of the Yangtze River mouth and northern Jiangsu were generally similar in geometry to the present ones. At these two stages (the 8th and the 11th centuries AD), the radial tidal current fields with a focal point in Dongtai area were evident, and the distribution patterns of tidal current fields were much similar than at present. After the 11th century AD, the northern Jiangsu shoreline evolved gradually to the present position under the influence of the, shifting Yellow River mouth and the present radial tidal current field, with its focal point in the Qianggang area, was formed eventually over the southern Yellow Sea. In short, the radial tidal current field off the PYRE and northern Jiangsu coast has existed and its distribution pattern has been quite stable since around 7000 years BP, despite the shoreline evolution of the PYRE and northern Jiangsu coast. However, the convergent location of the tidal currents has shifted from the mouth of the PYRE to the Dongtai area and then to the present Qianggang area. This suggests that the radial tidal current field in the RSR area existed before the formation of these sand ridges, and the RSR in the southern Yellow Sea were formed and are maintained by radial tidal current fields with sufficient sediment supply.