兴凯湖沉积物有机碳和氮及其稳定同位素反映的28kaBP以来区域古气候环境变化

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

兴凯湖是东北亚最大的淡水湖,也是中俄界湖。我们是国内首次对兴凯湖一根长269cm的沉积岩心进行了研究,结果显示:δ13Corg和TOC之间显示较好的负相关性,说明δ13Corg低值时期,气候温暖或湿润,δ13Corg值处于高值时期,气候冷干;C/N比值和TOC之间显示较好的正相关性,C/N比值平均值为11.4,显示兴凯湖沉积物有机质以内源浮游植物生产为主;δ15Norg高值对应于气候冷干期,此时沉积物有机质更多的来源于浮游植物,δ15Norg低值对应于暖湿期,但营养盐输入的减少也会造成δ15Norg值降低。兴凯湖沉积物有机碳和氮及其稳定同位素数据综合分析结果表明:28480～26160cal.aBP,湖区气候冷干;26160～22880cal.aBP,湖区气候温暖湿润;22880～18180cal.aBP,流域处于末次盛冰期多年冻土环境;18185～12650cal.aBP,对应于Blling/OlderDryas/Allerd气候波动暖期;90～78cm段,对应于YoungerDryas事件;11500～4570cal.aBP,进入全新世暖湿期,早期气候温干,晚期气候温湿;4570～1470cal.aBP,气候冷干;1470cal.aBP以来,又转为暖湿气候。

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 δ13Corg values are well within the range of-24.56‰～-27.67‰ derived from C3 vegetation,and the composition of δ13Corg in C3 plants increases with deceasing annual precipitation and temperature.So,sedimentary organic carbon in cold-dry periods is more enriched in 13C 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 δ15N 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.