不同时间尺度青海湖沉积物总有机碳对气候变化的敏感性

Total organic carbon sensitivity to climate change from Lake Qinghai sediments at different time scales

湖泊沉积物总有机碳(TOC)含量通常作为表征流域和湖泊生产力的指标,在亚洲季风区也常常被当作夏季风的代用指标,被广泛应用于气候与环境变化研究.本文梳理了过去千年、全新世以及冰期-间冰期时间尺度上青海湖沉积物TOC的变化特征,并探讨了其指示气候变化的敏感性与有效性.结果表明,过去千年青海湖沉积物TOC含量与区域暖季温度和降水表现出较为一致的周期性波动.通过对比全新世区域夏季温度、基于孢粉的降水定量重建结果,以及湖泊水位、风沙活动反映的湿度状况等,发现不能简单地将青海湖沉积物TOC含量或沉积通量作为夏季风强度或者季风降水强度的代用指标.青海湖沉积物TOC含量在冰期和间冰期表现出巨大的差异,指示了冰期-间冰期时间尺度上较大的温度与降水变幅.因此,不同地域条件及不同时间尺度下,湖泊沉积物TOC对气候变化的敏感性不同,将湖泊沉积物TOC含量作为亚洲夏季风的代用指标需要特别谨慎,特别是在高寒气候区.

Total organic carbon (TOC) content of lacustrine sediments has been widely used in the climatic and environmental studies as a proxy of productivity in the catchment and lake water;it is also used as an index of monsoon precipitation in the regions dominated by the Asian summer monsoon.In the present paper,we summarized the variation characteristics of TOC in Lake Qinghai sediments at scales of past millennium,the Holocene and the glacial-interglacial;and discussed the sensitivity and applicability of TOC for indicating climate change.The results indicate that the variation of TOC in Lake Qinghai sediments during the past millennium is consistent with that of regional warm season temperature,as well as the precipitation.After compared with regional summer temperature,pollen-based precipitation reconstruction results,and moisture evolution inferred from water level of lakes and aeolian activity history,we found that TOC content or flux cannot be regarded as a reliable index of the intensity of summer monsoon or monsoonal precipitation during the Holocene.TOC content from Lake Qinghai during the Holocene and the last glacial were distinctly different,indicating huge difference of precipitation and temperature at the glacial-interglacial scale.Therefore,the sensitivity of TOC in lake sediments to climate change is different at different places or different time scales;it should be very careful to use lacustrine TOC as an index of Asian summer monsoon intensity,especially in the cold and high-altitude regions.