Summer upwelling current in Weihai Bay and its contribution to transportation of suspended matters

This paper is devoted to the mechanism of summer upwelling current in Weihai Bay and its contribution to the transportation of suspended matters based on the observation data acquired from the instrumented tripods placed at the grid stations arround the bay mouth during the summer of 2018. The data studied includes water temperature, salinity, turbidity, water level, tidal current, satellite remote sensing data of SST and winds. Results show that the water temperature of the surface layer in the bay is below 23 ℃, about 4～5 ℃ lower than that of the outside water. Isotherms were climbing up shoreward and peaked near the bay mouth in a cone-shaped form, indicating the existence of upwelling current. With the change of local winds, the upwelling current changes in a cyclic pattern from stabilization, weakening, disappearance and recovery. The upwelling was supposed to be driven by southerly summer winds, and the local topography has a significant impact on its intensity. Under the action of southerly winds, water in the upper layer moves seaward, which causes the upwelling of cold bottom water flowing from the outside into the bay mainly through the southern mouth. Instead, the surplus water flows out of the bay through the northern mouth. The distribution of turbidity in the study area was well correlated with water temperature, the iso-contours of turbidity also bulge upward near the bay mouth. The re-suspended sediment off the Chengshantou Cape may be the main source of the mud deposit in the bay, the existence of upwelling current may reduce the settling velocity of suspended matters and drive the landward transport of the bottom water.