DYNAMICAL SIMULATION ON TIDAL CURRENT FIELD IN ANCIENT YELLOW SEA DURING YOUNGER DRYAS EPISODE

During Younger Dryas episode (12.9~11.6 cal. ka), the sea level oscillated at about -66 m depth contour in the continental shelf seas in eastern China and the seawater got into the south of the 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 is 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-dimension into two-dimension. The results show that the tidal current was still very strong in Yellow Sea during Younger Dryas episode, entering the special gulf along the right side entrance. From both shallow 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, tidal residual current flows to southeast and east with relatively great velocity at the west and interior gulf and it becomes weakly near the entrance. The current may carry the bottom sediments and discharge them to the 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 (Heishan mud zone). 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 eastern South Yellow Sea have a close relationship with the tidal current field of the ancient Yellow Sea, so the less fluctuating 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 the present Yellow Sea during Younger Dryas episode.