PALEOENVIRONMENTAL AND PALEOCLIMATIC CHANGES REFLECTED BY DIFFUSE REFLECTANCE SPECTROSCOPY AND MAGNETIC SUSCEPTIBILITY FROM XINGKAI LAKE SEDIMENTS

The Xingkai Lake, a transboundary lake by China and Russia, is the largest freshwater lake in Northeast Asia. We used diffuse reflectance spectroscopy and magnetic susceptibility to characterize the sediments in a 269 cm long core from deepwater in the northern part of the lake. Redness in sediment is primarily related to wet-warm climate,which seems to monitor paleoclimatic changes in the area; brightness has a good correlation with magnetic susceptibility,clay,TOC and redness, and likewise, magnetic susceptibility with clay. As lacustrine sediment becomes coarser, magnetic susceptibility generally decreases in the core.So both brightness and magnetic susceptibility can be used as a proxy indicator of palaeoclimate evolution in the area.Climate changes recorded by the lake sediments from Xingkai Lake were mainly characterized by the warm-wet and cold-dry alternation,based on accelerator mass spectrometry (AMS) radiocarbon chronology. An extreme cold-dry period occurred during 28 480~26 160 cal.aBP, especially during 27 050~26 160 cal.aBP.It was colder drier,with redness decreasing evidently.During 26 160~22 880 cal.aBP,redness reached the lowest value while climate transited to warm and wet conditions. 22 880~18 185 cal.aBP was a very cold period with very poor pollen grain in the sediments corresponding to the Last Glacial Maximum(LGM). 18 185~12 650 cal.aBP was a frequent oscillation period of redness and magnetic susceptibility correlating with Bølling/Older Dryas/Allerød warm period. A sharp fluctuation of redness, brightness and magnetic susceptibility occurred around the Younger Dryas cold event, at about 90~78 cm depth in the core. During 11 500~4 570 cal.aBP, redness increased to higher values, indicating a wet and warm climate in Holocene, and 8 000~5 000 cal.aBP represented Holocene Megathemal period(Holocene thermal optimum) with the highest redness value of the horizon in the area.During 4 570~1 470 cal.aBP,redness and magnetic susceptibility decreased markedly, reflecting the prevalence of cold-dry climate. Since 1 470 cal.aBP, frequency dependent susceptibility and redness increased drastically, climate became warm-wet again, and human activities resulted in remarkable increase of erosion and more terrestria1 material carried into the 1ake.