Impact of cold water mass on suspended sediment transport in the South Yellow Sea

Abstract

Cold water mass (CWM) is a distinct hydrologic phenomenon in summer in worldwide continental shelf seas. CWM can significantly affect circulation patterns and biogeochemical fluxes, and thus marine ecosystems. Nonetheless, limited studies have documented the seasonal migration of the CWM thermal front and the corresponding sediment distribution in the South Yellow Sea (SYS). This study used field observations and a well-validated numerical model to investigate the evolution of the CWM in the SYS; and its potential effect on the seasonal and spatial variations of suspended sediment distribution and transport. Remarkable seasonal variation in the CWM and its thermal front were observed from spring to fall. Numerical model results indicated that the reductions in current velocities and bottom shear stresses were induced by the baroclinic effect of the thermal front. Hence, the offshore sediment transport existed near the thermal front. The variations of intensity and location of the thermal front are capable of inducing the variation of suspended sediment concentration and sediment transport without winds. Sediment transport direction was slightly adjusted by winds. Northerly wind drove sediment transport seaward from the Chengshan Cape to the central SYS as the thermal front moved seaward in fall. Besides, the seaward extension of highly turbid water near the Subei coast in fall was also caused by wind-induced currents and waves. The thermocline of the CWM restricted the sediment from efficiently dispersing upward to the surface, which promoted the formation of the central SYS mud area. The understanding about the effect of CWM with its thermal front on the sediment transport in this study should benefit further exploring other CWMs on the continental shelf seas.