Millennial-scale paleoenvironment and paleoclimate changes recorded in the Bohai Sea sediments during the last glacial period

The millennial-scale paleoclimatic change during the last glacial stage has been recorded in various achieves worldwide, but nothing has been heard from the sedimentary records in a coastal zone. In order to dig out the sedimentary records from the coastal region, we carried out high-resolution grain-size analysis for the upper 26m of the core BH08 collected from the Bohai Sea, together with AMS ¹⁴C dating and microfossils studies. Based upon them, the paleoenvironment and paleoclimate changes of the study area since the last glacial stage are discussed. Grain-size data is treated with the grain size and standard deviation method. It is found that the sensitive component (88.4~148.7μm) of the core BH08 sediments well recorded the D-O (Dansgarrd-Oeschger) cycle of the last glacial stage: the content of the sensitive component (88.4~148.7μm) was low in warm periods, but high in cold periods. The cyclicities of sensitive component are also corresponding to the index reflecting the East Asian summer monsoon. During the warm periods, strong summer monsoon would bring in abundant precipitation, and the increased runoff might transport the coarse-grained sediments to the distant downstream areas. In addition, warm and humid climate is conducive to the development of vegetation, resulting in the reduction of coarse-grained sediments in the drainage basin, and vise versa. It is speculated that in the last glacial stage, climate in the high latitudes such as Greenland and the North Atlantic might cause changes in atmospheric circulation and/or ocean current systems by the precipitation of the East Asian summer monsoon, and thus control the changes of the input sediments from rivers. It may be the main reason for the change of grain-size in the core BH08.