3500年来祁连山中段天鹅湖岩芯记录的沉积环境变化

A 3500 Year Environmental Changes Recorded by Sediment of Tian'E Lake,Central Part of the Qilian Mountains,China

湖泊沉积,特别是内陆高山封闭湖泊沉积是古气候研究的重要载体,可以高分辨率、敏感地记录连续的古气候环境变化。选取祁连山中段天鹅湖沉积岩芯TEB孔的10个陆生植物残体进行AMS^(14)C测年并建立年代框架,结合对总有机碳(TOC)含量、矿物成分及元素相对含量等指标的分析结果,重建了天鹅湖3 500年来的沉积环境变化特征。初步研究结果表明:碳酸盐含量变化主要受控于地下水补给量的变化,进而反映区域降水量,1 534 BC^1 300 AD期间,天鹅湖区降水呈减少的趋势,尤其是中世纪暖期(720~1 300 AD),是3 500年来最干旱的时期;小冰期开始于1 300 AD,共出现三次降水较多的时期,1 600~1 730AD为小冰期最盛期。受西风环流影响,天鹅湖沉积记录了该区域中世纪暖期相对暖干,而小冰期较为冷湿的变化特征。同时,该湖记录的小冰期气候相比于中世纪暖期更不稳定。

Lake sediments, especially the inland-mountain closed lake sediments may record changes of continuouspaleoclimate, which is one of the important archives for paleoclimate reconstruction. Sediment core retrieved from theTian＇E Lake （TE Lake） in the central part of the Qilian Mountains was used to reconstruct climatic changes duringthe past 3 500 year based on the analysis of total organic carbon （TOC）, elemental and mineral compositions. Thechronology of TEB core was established using AMS 14C dates of ten terrestrial plant residues. The results showed thatcarbonate content was controlled by the supplementary of groundwater, further indicating the precipitation around thecatchment. Accordingly, the precipitation of TE Lake had a decreasing tendency between 1 534 BC-1 300 AD basedon carbonate content. Especially during the Medieval Warm Period （MWP） （ 720-1 300 AD）, the precipitationreached the lowest values in the last 3 500 years. There were three-times of humid conditions during the Little Ice Age（LIA） which began at 1 300 AD and reached the most humid condition during the period of 1 600-1 730 AD. TELake was characterized by assembly of warm-dry and cold-wet climate transitions in the region resulted from the influ-ence of Westerlies. Moreover, variations of local climate during LIA recorded by TE Lake sediments were more unsta-ble than that during the MWP.