青藏高原巴松措年纹层记录的200年以来气候环境演化

A Global Warming Hiatus, i.e. a period of relatively little change in globally averaged surface temperatures, began in the end of last century (ca. 1998 A.D.). However, an obviously warming trend was observed from the Tibetan Plateau especially the southeastern Tibetan Plateau (SETP) during this period. The responding process of regional climate and environment changes to global climate change during the past 200 years needs further investigation. We choose Lake Basom Tso in SETP as our study area. Varve counting, 210Pb/137Cs dating as well as AMS 14C dating will be used to establish the age-depth model for the sediment core recovered from the lake center. The mechanism of the varve formation and the palaeoclimatic indication of varve thickness will be investigated through seasonal monitoring on the modern sedimentation process. Subsequently, the varve thickness and sedimentary proxies, i.e. grain size, Total Organic Carbon content (TOC), mineral and element compositions, will be used to trace the environmental changes during the varve formation. The fossil pollen record will be interpreted in terms of changes in the regional vegetation. Finally, the climate-vegetation variations in Lake Basom Tso region during the past 200 years will be reconstructed at an annual resolution, which will be compared with regional and global records, as well as simulation results, in order to investigate the responding mechanisms of the climate changes over SETP to global warming. This project could provide further insights to the annual scale variations of past climate and vegetation changes over the SETP, the variation of Asian Summer Monsoon during the recent past, as well as the underlying drivers.

全球气候变暖自上世纪末期出现停滞，而青藏高原尤其是其东南部地区仍存在明显的升温趋势，该区域过去200年高分辨率气候环境演化及其对全球变化的响应有待深入研究。本项目选择青藏高原东南部的巴松措，利用年纹层计年、210Pb/137Cs及AMS 14C测年结果，建立可靠的沉积物年代序列；在对湖泊现代沉积物季节性监测分析的基础上，结合沉积物岩芯年纹层的结构及组成特征，揭示年纹层的形成机制及纹层厚度的气候环境指示意义；利用年纹层厚度及年分辨率的气候代用指标（粒度、有机碳含量、矿物及元素组成等）探讨年纹层的形成过程及沉积环境特征；并通过孢粉记录重建区域的植被演化过程；在此基础上，建立巴松措地区过去200年以来的年分辨率气候环境演化序列。通过对比分析，探讨青藏高原东南部地区气候环境对全球气候变化的响应模式，为充分理解青藏高原东南部地区年分辨率的古气候演化模式、夏季风演化过程以及相应的驱动机制提供科学依据。

湖泊沉积物是记录气候演化信息的重要载体之一，在探讨过去气候变化过程研究中发挥重要作用。然而，沉积物中的许多代用指标对气候的指示意义存在多解性，不同指标所反映的环境信息相互之间有时会存在矛盾。为了能够更准确地解读湖泊沉积物中指标所记录的环境变化信息，开展现代湖泊沉积物指标与环境之间的关系研究，深入探讨各指标对环境变化的响应机制尤为关键。本项研究利用青藏高原东南部巴松措湖泊表层沉积物作为研究对象，利用210Pb与137Cs比活度检测结果建立年代序列，对沉积物中粒度、磁化率、有机质含量等指标进行分析，揭示巴松措现代沉积过程。结合沉积物粒度端元组分分析结果，并将不同指标变化与林芝气象站所记录的数据资料进行对比，得出以下主要结论：该地区沉积物来源主要包括径流搬运的冰川碎屑物质和来自青藏高原南部、西南部上空悬浮于大气中的风成物质两部分；其中，通过风力搬运的物质输入主要集中在冬半年，受季节性风向及风速变化影响明显；径流受到冰雪融水与夏季降水的补给，因此通过径流搬运的物质输入量受到温度与降水综合影响；湖泊中磁性矿物碎屑的产生和输入主要受区域降水量影响的流域侵蚀速率变化控制，该湖泊沉积物磁化率波动可以有效的指示该地区降水量变化；沉积物中TOC, TN含量变化主要反映湖泊自身初级生产力的变化，对区域温度变化的响应显著。该现代过程研究结果对于利用湖泊沉积物重建青藏高原东南部地区气候演化过程具有重要参考价值。此外，利用巴松措沉积物岩芯岩性变化、XRF元素扫描结果等获取到了湖泊沉积物中所保存的地震事件证据，在利用湖泊沉积物获取长时间序列地震历史记录、探讨地震事件发生规律以及对未来地震进行有效预测方面可提供重要科学依据。