Environmental evolution and impact of the Yellow River sediments on deposition in the Bohai Sea during the last deglaciation

摘要

Samples of one core in the Bohai Sea mud area (BSMA) were analyzed in grain size, magnetic susceptibility (MS), major minerals, foraminifera, ostracod, stable isotopes, and ~(14)C dating to reconstruct sedimentary environment and impact of the Yellow River sediments on deposition in the Bohai Sea during the last deglaciation. The central Bohai Sea was river mouth or swamp environment before 12.9 ka BP, when sediments with low MS values had high sand content. Appearance of two peat layers at 11.2 and 12.9 ka BP at Core M7-6 showed that seawater had not yet entered the central Bohai Sea, where the limnetic ostracod was frequently existed and foraminifera were hardly seen. Abundance and diversity of foraminifera began to increase sharply, while their oxygen and carbon isotopes became heavier from ～9.3 ka BP due to seawater entrance into the central Bohai Sea. Related to intrusion of the Yellow Sea Warm Current (YSWC) extension into the central Bohai Sea, oxygen and carbon isotopes reached the maximum at ～6.5 ka BP. MS values between 2.4 and 8.3 ka BP increased continually together with slow sedimentation rate, revealing that the impact of the Yellow River sediments was limited because of strong hydrodynamic condition and small sediment discharge. At the last 2.4 ka, the influence of the Yellow River reached the maximum due to large sediment discharge into the Bohai Sea. However, the BSMA had slow sedimentation rate compared with other mud areas in the Chinese marginal seas despite of its close distance from the Yellow River mouth, indicating that although the BSMA was the primary sink of the Yellow River sediments, most of the Yellow River sediments were deposited at other areas (e.g. deltaic areas and Shandong mud wedge).