Paleoenvironment Evolution Of Beijing Plain Since The Late Pleistocene

In recent years, human are eager to further understand the processes of paleoenvironmental evolution and predict the variations of future climate change. Climate oscillations during Late Pleistocene, including the last glacial-interglacial cycles, can largely reveal the features of Quaternary climate and predict future environmental changes. Beijing, located in the sensitive transition region of sub-humid to semi-arid areas, can better reflect the history of environmental evolution since the late Pleistocene. By the aid of high-density sampling and OSL dating, this study analyzed the paleoenvironmental changes and the 104-103-year scales climatic variations in Beijing plain since the Late Pleistocene bases on the characteristics of the organic carbon isotope, CaCO₃ content and granularity in Changping borehole. In comparison with the results from Greenland ice core and deep-sea oxygen isotope records, we also study their possible driving mechanisms in the study area.Our results show that the temperature is the main controlling factor ofδ¹³C_org value, while CaCO₃ content and granularity mainly related to the precipitation. Four climatic stages are evident in Beijing Plain since the late Pleistocene, including the last interglacial period （MIS5; before 76 ka B.P.）, the early glacial step （MIS4; 76-56 ka B.P.）, the interglacial step （MIS3; 56-18 ka B.P.） and the late glacial step （MIS2; 18-13 ka B.P.）, and in which each stage can be divided into a number of sub- variations.The climate changes in Beijing Plain since the late Pleistocene share similar millennial scale climate changes with those in domestic Loess, the GRIP ice core, the deep-sea sediments in North Atlantic. Our results reveal several distinct 103-year scale climatic oscillations evidently represented by the cold events （H1-H9） and warm Bond cycles （1, 2, 4, 8, 12, 17, 18, 19, 20, 21, 23）, indicating the instability of the Asian monsoon system and its coupling processes with last glacial-interglacial cycle.The results also revealed a certain delay in the late MIS3 compared with those in Greenland, with a relatively warm period and the winter monsoon weakening in the late MIS3. In addition, the Asian monsoon enhanced more quickly than that of GRIP oxygen isotope record, and the H events varied greatly. The existence of differences in the context of global climate changes actually reflected the regional paleo-environment variations. winter and summer monsoons were mainly driven by global ice volume. On a short time scale, there might be other driving factors, instead of Milankovitch theory, to control the short-term climatic events. One probable reason for the different onsets of these prompt changes might be the contribution of local underlying factors, with topographic, hydrographic, meteorological patterns and other more complex drive mechanism being the predominant controls.