Paleoenviromental and Paleoclimatic Changes in Lake Xingkai Inferred from Stable Carbon and Nitrogen Isotopes of Bulk Organic Matter Since 28kaBP

Key words: 
• organic carbon and nitrogen isotope

Abstract: Xingkai Lake, a transboundary lake by China and Russia, is the largest freshwater lake in Northeast Asia. A 269 m long continuous sediment core, approximately 28 kaold at the bottom, from Lake Xingkai, has been analyzed first in China for the stable isotopes of carbon, nitrogen, TOC and C/N ratios, in order to study the paleoclimatic and paleoenviromental changes in the area. The result showed that all δ13Corg values are well within the range of 24.56‰～27.67‰ derived from C3 vegetation, and the composition of δ13Corg in C3 plants increases with deceasing annual precipitation and temperature. So, sedimentary organic carbon in colddry periods is more enriched in 13C than that in warmwet periods. Low TOC, which are typical for lower temperatures, coincided with lower C/N ratios, reflecting that in cold period the sedimentary organic matters mainly derived from aquatic organic matters which have higher δ15N values than terraneous organic matters. These results enable us to reconstruct the evolution sequence of paleoclimate in Xingkai Lake region, 28 480～26 160cal.aBP, the climate was cold and dry;
26 160～22 880cal.aBP, the climate became warm and wet; 22 880～18 185cal.aBP correspond to the Last Glacial Maximum(LGM); 18 185～12 650cal.aBP, it was an frequent oscillation period corresponding to Blling/Older Dryas/Allerd warm period; Younger Dryas cold event occured at about 90~78 cm depth in the core; 11 500～4 570 cal.aBP, climate became wet and warm gradually, in which it was temperaturedry in early stage and temperaturewet in late stage, but 8 000～5 000 cal.aBP was Holocene Megathemal period(Holocene thermal optimum)in the area; During 4 570～1 470 cal.aBP, it was a colddry climate, and since 1 470 cal.aBP, climate became warmwet again.