全新世以来湖泊沉积记录的西南季风与东南季风演化过程比较研究

Studying impacts of long-term Asian summer monsoon changes on hydroclimatic processes and characteristics is important to understand the mode of floods and droughts in monsoon regions and plays a significant role for the sustainable development of society and regional ecological environment. Previous studies have shown very different and sometimes event opposite conclusions about Holocene climate changes in terms of the long-term trend and abrupt climatic events between southwest and southeast Asian monsoon regions. It is essential that more well-dated and high-resolution paleoclimatic records are needed for understanding the variability and abrupt changes in Asian summer monsoon in geological time, which would help to project future changes in monsoon precipitations and evaluate its influences on water resources in southern China under global warming conditions. In this study, we propose to analyze sediment cores from two alpine lakes, one from the southwest monsoon region and another from the southern margin of southeast monsoon region. Based on reliable chronological models, we try to reconstruct high-resolution records of temperature, precipitation, and effective moisture during the entire Holocene, by analyzing multiple proxies including chironomid assemblages and δ18O values of chironomid head capsules, δD values of short- and long- chain n-alkanes, and continuous XRF core scanning for relative elemental compositions. We will compare the results from these two lakes to test whether it is different for Holocene climate trends and climate events between southwest and southeast monsoon regions. Furthermore, in combination with paleoclimatic models, we will compare our results with other regional and global data-sets to better understand the dynamics of Asian summer monsoon on centennial- to millennial- timescales.

研究长时间尺度亚洲季风演化导致的中国西南和南方地区区域水文气候变化过程与特征，对认识洪涝/干旱模式及其对社会和生态环境重大影响具有重要意义。全新世以来西南季风和东南季风的长期演化及突变事件的干湿区域差异及动力机制还存在不同认识，本申请拟开展西南季风区与东南季风区南缘两个山地湖泊的沉积物岩芯分析，以可靠的定年为基础，利用摇蚊组合、摇蚊头壳的氧同位素指标，重建两个湖区全新世以来温度变化序列；利用长链和短链正构烷烃氢同位素、结合高分辨率XRF岩心扫描元素结果，重建季风降水和有效湿度的变化序列。探讨全新世以来西南季风和东南季风的长期演化及主要气候事件是否为同步，中世纪暖期及小冰期湿度变化与南海地区变化趋势是否一致；进而通过区域和全球对比，结合古气候模拟的结果，探讨在百年至千年不同时间尺度上亚洲季风演化的动力学机制。理解全球暖化背景下季风变化趋势及其对我国西南和南方水资源的影响。

本项目选择西南季风区西盟龙潭和东南季风边缘区的八仙天池为主要研究对象，通过高分辨率的钻孔年代学、沉积学、地球化学和生物学等手段比较研究了全新世以来西南季风和东南季风演化过程。创新性使用摇蚊-温度转换函数方法和生物标志化合物—温度重建公式方法定量重建了两季风区全新世以来的温度变化；结合高分辨率XRF岩芯元素扫描结果和粒度分析结果，获得了全新世西南季风演化的高分辨率的记录，探讨了年代际到百年尺度上季风突变事件的变率和变幅及其驱动机制；利用沉积岩芯黑炭通量重建全新世火事件发生历史，通过与温度和降水进行对比，探讨了火事件与气候变化及人类活动之间关系；通过与已有资料对比，探讨了全新世以来两季风区气候变化的驱动机制。