The role of wind in the multi-year variations of surface suspended sediment in the Bohai Sea

The multi-year variations of suspended sediment concentration (SSC) in the Bohai Sea have important impacts on the water quality and ecosystem. In recent years, the river-delivered sediments, especially from the Yellow River, have decreased significantly. As one of the influencing factors, wind has become the main factor affecting the long-term changes of SSC in Bohai Sea. Based on the moderate resolution imaging spectrometer (MODIS) L1B data from 2003 to 2021, this paper established an inversion model combined with the measured SSC from several voyages in the Bohai Sea to obtain the multi-year data of the surface SSC in the Bohai Sea. And the empirical orthogonal function (EOF) method was used to analysis the spatial and temporal patterns of the surface SSC in the Bohai Sea. Furthermore, the climate forecast system reanalysis(CFSR) wind data were collected to explore the role of wind field in the multi-year variations of the surface SSC in the Bohai Sea. The results of EOF analysis of the SSC showed that the cumulative variance contributed by the first three modes was 73.4%. The first mode contributed 53.15% to the overall variance and was dominated by the synchronous variation of the whole sea area. This mode was mainly controlled by the wind speed change in winter, which indicated that the SSC increased with the enhanced winter wind speed before 2009 and decreased with the weakened winter wind speed after 2009. The second mode contributed 14.14% to the overall variance and showed the variation characteristics of the inverse phase of SSC in Bohai Bay and Laizhou Bay, which was related to the advective transport of sediment controlled by the wind direction. The study of long-term changes of the SSC in the Bohai Sea and the exchange of sediment between different bays are important scientific supports to the ecological environment protection in the Bohai Sea. And the results can also be used to predict the change of coastal geomorphology and seabed disaster.