Dynamical simulation and analysis of the tidal current field in Yellow Sea during Younger Dryas Period

摘要

During Younger Dryas period (12.9～11.6 cal. ka), the sea level oscillates at about -66m depth contour in the continental shelf seas in eastern China and the seawater gets into the south of present North Yellow Sea. So Yellow Sea became a long narrow channel gulf. To simulate the tidal current of this special gulf, Environmental Fluid Dynamics Computer Code (EFDC) was used in this paper. The calculation combines curvilinear orthogonal coordinates in the horizontal direction with Sigma mapping coordinates in the vertical direction, and it uses a method which transforms a problem from three-dimensional into two-dimensional. The results show that the tidal current is still very strong in Yellow Sea during Younger Dryas period, entering the special gulf along the right side entrance. From shallow both sides to deep centre, rotating flow changes reciprocating flow. Under the effect of reciprocating flow, the floor is eroded and the mud and sand are carried away. Progressive wave turns into rotating wave and two ateliotic amphidromic points appear on the western side of the gulf after tidal wave coming into Yellow Sea. At the same time, the tidal residual current flows towards southeast and east at relatively high velocity while at the west and interior gulf and it becomes weak near the entrance. The current may carry the bottom sediment and discharges them at the location of present mud sediment zone in north East China Sea. But at eastern Yellow Sea the tidal residual current flows to north and forms an anticlockwise circulation at centre of the eastern gulf which is corresponding to the eddy mud zone in Southeast Yellow Sea. The anticlockwise circulation captures suspended sediment and may gestate the present mud sediment zone. The extension direction of tidal sand ridges and the size composition of the tidal current sand in East South Yellow Sea have a close relationship with the tidal current field of the ancient Yellow Sea, so the fluctuating lesser sea level changing and the relative stable tidal current field are the favorable factors for the tidal sand ridges during Younger Dryas Episode in ancient Yellow Sea. It can be said that the ocean current, tidal current and tidal residual current figure the pattern of present Yellow Sea during Younger Dryas Period.