末次盛冰期以来云南异龙湖的环境演变——来自地球化学沉积记录的证据

通过对云南异龙湖4.56 m沉积岩芯进行X射线荧光光谱分析(XRF),结合13个AMS14C测年结果,获得了高分辨率元素地球化学序列。异龙湖岩芯中元素的因子分析显示,F1因子揭示了沉积地球化学元素的来源,其正载荷代表了流域外源物质输入加强,而负载荷则指示了湖泊自生碳酸盐沉淀的增加,F2因子指示了湖泊氧化还原状态,F3因子可能与人类活动有关。在此基础上结合磁化率、矿物组成及有机质含量等指标,对异龙湖沉积环境演化过程进行探讨。结果表明,在末次盛冰期期间(26000—17000 cal. yr. BP),区域气候特征是气温低、降水少;在17000—14500 cal. yr. BP期间,异龙湖经历了显著的干旱气候,可能与亚洲夏季风突然减弱有关; 14500—9000 cal. yr. BP,异龙湖经历了显著的高湖面阶段,与滇池高水位时期基本一致,表明流域降水丰沛,外源物质输入增加; 9000—6000 cal. yr. BP期间,区域温度增加导致流域干旱化加剧,此阶段与西南地区全新世大暖期(全新世适宜期)相对应; 6000 cal. yr. BP以后外援物质输入锐减可能指示了区域降水的降低。异龙湖地球化学沉积记录揭示的环境演变过程与区域气候环境变化具有一致性,也具有明显的特殊性。

Hydroclimate changes since Last Glacial Maximum: geochemical evidence from Yilong Lake, southwestern China

Using X-ray fluorescence scanning and AMS ¹⁴C analyses, we present a geochemical record of a 4.56 m long sediment core from Yilong Lake, Yunnan Province, southwestern China. Factor analysis of the geochemical elements revealed three factors, F1, F2, and F3. F1 indicates the sources of sedimentary geochemical elements, with its positive loads relating to the increased input of exogenous materials and negative loads showing increased authigenic carbonate precipitation. F2 indicates a lacustrine redox state. F3 is probably relating to human activities. Here, we discuss the process of climate and environmental changes, based on variations in the geochemical records, as well as the magnetic susceptibility, mineral compositions and organic contents. During Last Glacial Maximum, from 26,000 to 17,000 cal. yr. BP, a relatively cold and dry climate dominated this region. The climate trended to be drier, probably in relation to the rapid decrease in monsoonal precipitation from 17,000 to 14,500 cal. yr. BP. After 14,500 cal. yr. BP, the water level in Yilong Lake rose, lasting until 9000 cal. yr. BP. This high lake level was consistent with that of Dianchi Lake, indicating a regional humid condition in response to an increase in monsoonal precipitation. From 9,000 to 6,000 cal. yr. BP, the regional temperature increased in response to the Holocene Megathermal Maximum. After 6,000 cal. yr. BP, a decreased in exogenous materials indicates that the regional precipitation probably decreased. Although the hydroclimate evolution of Yilong Lake is consistent with the effects of regional climate change, it is also with obvious particularity, and more studies are needed to gain a comprehensive understanding of the regional historic environment change.