末次盛冰期以来西南季风的量化研究：湖泊沉积生物标志物和单体氢同位素记录

Using high-resolution well-dated paleoclimate records to study the history of Southwestern Monsoon and the characteristic of abrupt climate events, would help to predict future changes in monsoon intensity under a global warming scenario and to evaluate its potential effects on water resources in southern China. However, traditional paleo-proxies still have many uncertainties because of potential influences of multiple processes, thus leading to inconsistent and sometimes even conflict conclusions. The development of analytical techniques for biomarkers and compound-specific hydrogen isotopes might be helpful to solve this issue. In this project, the PI propose to collect sediment cores from two lakes with different types in the Southwestern Monsoon region. The high-precision chronology of sediment cores will be established using radiocarbon dating of well-preserved terrestrial plant fragments. Based on a systematic study of modern process at these two lakes, high-resolution records of quantitative temperature, monsoon intensity, and effective moisture will be reconstructed since the last glacial maximum by GDGTs, compound-specific hydrogen isotope of long-chain alkanes, and the differences of compound-specific hydrogen isotope between short-chain and long-chain alkanes, respectively. By comparing the resulted records between these two lakes, the responses of different-type lakes to abrupt climate events will be distinguished and evaluated. By comparing with other records at regional- and hemisphere-scale, aided with the results from paleoclimate models, the underlying dynamics of Southwestern Monsoon will be investigated from centennial- to orbital-scale since the Last Glacial Maximum.

利用定年可靠且分辨率高的古气候记录研究地质时期西南季风演化机制和气候突变事件特征，能帮助理解全球暖化背景下季风变化趋势及其对我国南方水资源的影响。但是目前所采用的很多古气候指标，其指代意义还存在不确定性，导致了认识偏差甚至相互矛盾的结论。生物标志物及单体氢同位素分析技术的发展有望解决这一困境。本项目选择我国西南季风区两个不同类型湖泊为研究对象，提取末次盛冰期以来湖泊沉积岩芯，用保存较好的陆源植物残体进行AMS-14C测试以建立准确的年代标尺。基于系统的现代过程研究，分析测试GDGT定量重建年平均温度变化序列，用长链正构烷烃单体氢同位素重建季风强弱变化，用短链和长链正构烷烃单体氢同位素的差值重建有效湿度变化序列。通过两个湖泊中多指标记录对比，研究西南季风区不同类型湖泊对气候突变事件响应的差异。通过区域和半球尺度对比，结合古气候模拟结果，探讨末次盛冰期以来不同时间尺度西南季风演化的动力学机制。

利用定年可靠且分辨率较高的古气候记录研究地质时期西南季风演化机制和气候突变事件特征，能帮助理解全球暖化背景下季风变化趋势及其对我国南方水资源的影响。但是目前所采用的很多古气候指标，其指代意义还存在不确定性，导致了认识偏差甚至相互矛盾的结论。生物标志物及单体氢同位素分析技术的发展有望解决这一困境。本项目选择我国西南季风区泸沽湖和天才湖两个不同类型湖泊为研究对象，在系统的现代过程分析的基础上，利用沉积岩芯中brGDGTs指标重建了末次盛冰期以来西南地区定量温度记录，同时利用长链正构烷烃单体氢同位素重建了季风强弱变化序列。结合区域和全球已有记录，以及古气候模拟结果，西南地区冰消期温度上升与全球温度结果一致，由温室气体控制，而全新世以来年均温变化呈上升趋势，反映出低纬度地区的独特性。同时，单体氢同位素结果与已有的石笋氧同位素结果一致，全新世呈下降趋势。这一结果反映西南季风区年均温和夏季风变化之间的不同步变化，揭示了低纬度地区温度和季风强弱的季节性特点。