Distribution of Surface Sediment in the Bohai Sea and its Relationship with Sediment Supply and Sedimentary Dynamic Environment

The Bohai Sea is a semi-enclosed sea surrounded by the mainland and the Liaodong Peninsula. Numerous rivers flow into the Bohai Sea from mainland China, carrying lots of terrestrial sediment. Moreover, the hydrodynamic environment in the Bohai Sea has significant seasonal variability as modulated by the monsoonal climate. Therefore, the distribution and dispersal mechanism of the terrestrial sediment are very complicated and attract a wide spread attention. Based on the grain-size analysis of surface sediment recently sampled in the Bohai Sea, we discovered that owing to the influence of sediment supply and hydrodynamic environment, the surface sediment in the Bohai Sea were primarily composed of silty sand and clayey silt. In addition, the Yellow River delivered the highest amount of water and sediment discharge to the Bohai Sea, and thus affected the distribution of surface sediment in many areas, such as the Bohai Bay, the center of the Bohai Sea, etc. The coarse-grained areas were mainly distributed in the river mouth with relatively coarse river-laden sediment and strong hydrodynamics. Meanwhile, combined with the published sedimentation rate in the Bohai Sea, we found that there was an obvious spatial corresponding relationship in the Bohai Sea among the modern sedimentation rate, the grain-size distribution characteristic of surface sediment and sediment transport pattern. When the grain-size of the surface sediment was relatively coarse, the sedimentation rate of the region became low and the sediment converged towards fine-grained sediment areas; whereas the sedimentation rate was relatively high at the fine-grained sediment areas. Furthermore, the grain-size trend analysis showed that the fine-grained sediment areas, such as the center of the Bohai Sea and the northern of the Liaodong Bay where sedimentation rate was high, were the convergent center of surface sediment, except for the Bohai Bay and the subaqueous Yellow River Delta where offshore sediment transport was evident.