季风边缘区湖泊沉积记录的全新世气候变化

There were many global centennial to millennial scale climatic fluctuation events during the Holocene, and further study on the climate instability record and changing process of that period is extremely important. The Chagan Nuuer Terminal Salt Lake(Sunite right banner of Inner Mongolia) from the monsoon marginal area, which is very sensitive to the climate changes, was selected for studying the climatic fluctuation events during the Holocene. Research showed that there are five deposition layers of evaporite rocks in the Chagan Nuuer Lake's center section, among them are black clay layers of various thickness, which reflected the evolution of the wet and dry climate sensitively. By researching the alkali layer sequence and the mineral element composition and combination of characteristics of salts the number of dry events and the properties of droughts were confirmed. And the reconstruction of lake evolution time series and the determination of the drought event time scale were carried out by studying the alkali U-series dating, C-14 dating of profile inclusions and the AMS in plant residue of the clay profile, and OSL dating of the clay profile. Then by measuring the elevations of lake shorelines and OSL dating of beach sand, the spatial and temporal pattern of the high lake period was rebuilt. Through the analysis of oxygen and carbon isotopic indicators of various proxies, trace elements and authigenic carbonate of the section, the record of the sedimentary environment was recovered and the high-resolution process of paleoclimate evolution was reconstructed. Finally, comparison on drought events and monsoon evolution revealed the response of arid areas to global changes and the mechanism of drought events.

在全新世全球范围内曾发生多次百年至千年尺度的气候快速突变事件，深入研究该时段的气候不稳定性记录和变化过程极为重要。本项目选择季风边缘区终屡湖-察干诺尔（苏尼特右旗）盐湖为对象，开展全新世气候快速变化研究。该盐湖中心剖面有5层蒸发岩沉积，其间夹有厚度不同的黑色粘土层，能够敏感地反映气候干湿演变历史。通过碱层序列，结合盐类矿物元素成分和组合特征，确认干旱事件次数和干旱性质；开展剖面碱层的U系测年和包裹体的C-14测年，结合剖面各粘土层的OSL测年，对粘土中的植物残体进行AMS C-14定年，重建湖泊演化时间序列，厘定干旱事件时间标尺；开展湖岸堤高程测量和湖滨砂的OSL定年，恢复高湖面时期的时空格局；通过对剖面的各代用指标、元素地球化学和自生碳酸盐的氧、碳同位素指标分析，恢复其沉积环境记录，重建高分辨率的古气候演化过程；通过干旱事件与季风演化的对比，揭示全球变化的干旱区响应及其机理机制。

通过大范围的野外考察，确认在察干诺尔盐湖周围发育系列湖岸阶地，是湖面波动的重要标志。通过对各剖面点湖泊沉积物的C-14测年和植物残体的ASMC-14测年以及OSL测定年代，获得如下结论：1、察干诺尔古湖鼎盛时期为MIS5阶段（>100 ka），当时古湖向西北延伸，其范围扩展至蒙古国的南戈壁地区，形成巨大古湖。2、在MIS3阶段的60-29 ka、冰消期的18-14 ka和早全新世的8.2-8.0 ka分别发育较高的湖面，其面积分别达到3600、550和340 km2。但是湖面逐渐下降的总趋势，与现在的盐湖环境迥然不同。3、在早中全新世的6900-6230 Cal a BP期间湖泊经历了严重的衰退，其中在6900-6805 Cal a BP、6788-6540 Cal a BP和6540-6230 Cal a BP时段堆积石盐层，证明湖面下降，标志着干旱事件的发生。4、通过年代数据的比对发现，多数C-14年代数据存在333-7736a碳库效应，而且剖面上部受到的老碳作用要比底部大。