Controlling Factors and Dynamic Mechanisms of MultiDecadal Changes of Suspended Sediment Concentration in the Bohai Sea

Abstract Global climate change and human activities jointly drive the long‐term changes of suspended sediment concentration (SSC) in the ocean, including high turbidity coastal seas such as the semienclosed Bohai Sea. In the past few decades, SSC in the Bohai Sea has exhibited a significant decreasing trend according to satellite observations. In this study, a regional numerical model is employed to carry out sensitivity experiments to quantify the relative contributions of several controlling factors to this multidecadal SSC decline in the Bohai Sea. The model results suggest that reduction in wind speed (by 20% over the past 40 years) can cause the largest decrease (8 mg L −1 , 32%, with values close to satellite remote sensing data) in SSC averaged over the Bohai Sea, associated with a decrease (17%) of wave‐induced bottom shear stress. The coastline and bathymetry changes, due mainly to sediment discharge of the Yellow River, cause large SSC changes at local scales. Since 1976 when the Yellow River mouth was relocated from Bohai Bay to Laizhou Bay, sediment deposition led to significant shoaling in the new estuarine area. This can increase the bottom shear stress by over 50% and the local SSC by more than 30 mg L −1 and an increase (2 mg L −1 , 8%) in SSC over the Bohai Sea. The quantification of contributions from different controlling factors can help to predict long‐term SSC changes in the Bohai Sea, and the method of this study can be applied to other coastal regions where such quantifications are still lacking.