藏东南巴松措高分辨率硅藻千年记录及其对气候变化的响应

Understanding the ecological effects of climate changes is of great important for lake ecological environment assessment and restoration. There are plenty of lakes on the Tibetan Plateau. This region is very sensitive to climate changes, and has very less human activities. It thus becomes an ideal site for studying the lake ecological effects of climate changes. The past millennium has experienced obvious climate changes from Medieval Warm Period to Little Ice Age then to Current Warm Period, and thus become the important interval for discussing the impact of climate changes on lake ecosystems. We choose Lake Basom Tso in southeastern Tibetan Plateau as our study area. High-resolution diatom records from Lake Basom Tso will be used to reconstruct the changes in diatom assemblage structure and productivity during the past millennium. Combined with existing lake proxies (pollen, grain size, magnetic susceptibility, total organic carbon) and tree ring-reconstructed temperature data, the mechanisms underlying the responses of diatom assemblage to climatic changes will be analyzed, and the tipping point of diatom assemblage changes and the temperature threshold will be determined. By comparing with other diatom records from the southeastern Tibetan Plateau and analyzing the differences in morphology and geography of each lake and catchment, the similarities and differences of the diatom assemblage changes in Lake Basom Tso will be elucidated. It is expected that the information obtain from this study will provide scientific data for further understanding the ecological effects of climate changes, and historical similarity for predicting and evaluating the potential influence of future climate changes on lake ecosystem.

了解自然条件下湖泊生态系统对气候变化的响应模式对现今湖泊生态环境评估和修复意义重大。青藏高原地区湖泊密布，人类活动微弱，对气候变化敏感，是研究气候变化下湖泊生态效应的理想场所。过去1000年经历了中世纪暖期、小冰期和现代暖期3个显著气候变化过程，是探讨湖泊生态系统对气候变化响应的重要时段。本研究以青藏高原东南部巴松措为研究对象，利用高分辨率硅藻记录重建过去1000年硅藻群落结构和生物量变化历史；结合其它湖泊沉积代用指标（孢粉、粒度、磁化率、总有机碳）和树轮重建的温度数据，分析以硅藻为代表的湖泊生态系统对气候变化的响应机制及群落产生显著变化的温度阈值；对比青藏高原东南部其他湖泊硅藻记录，揭示巴松措硅藻群落变化的特性和共性，并从湖泊和流域的形态学和地理学特征探讨其产生原因。本研究将为青藏高原气候变化的湖泊生态效应提供进一步认识，并为未来气候变化对生态系统影响的评估提供科学依据。

青藏高原东南部气候变化已经对湖泊生态系统产生影响。然而，气候与非气候因子的同期变化以及流域过程对气候信号的调节作用使得理解气候变化对湖泊生态系统的影响变得复杂。并且，该地区湖泊生态与陆地植被对气候变化响应的异同也尚不清楚。因此需要长期、高分辨率的多变量时间序列进行分析。本项目主要采用了具有亚年代际分辨率的、近千年的巴松措湖沉积物硅藻和孢粉记录进行研究。硅藻优势种主要为浮游种，属种组合变化主要表现为大型和小型Pantocsekiella ocellata之间的转变以及浮游种和底栖种之间的转变。17世纪末以来大型P. ocellata的减少和小型P. ocellata的相应增加，以及硅藻生产力的上升主要反映了百年尺度上的气温上升。近千年的浮游种和底栖种丰度比值（P：B）出现了数次数年-数十年时间尺度的突然而快速的转变，表现为底栖硅藻的突然增加，是对沉积事件的响应。互相关分析揭示了硅藻对区域温度变化的同步响应和陆生植被对区域温度变化的异步响应，表明湖泊硅藻对青藏高原东南部气候变化的时间和幅度具有较高的敏感性。本项目的研究结果表明，在未来的气候情景下，巴松措和藏东南其它高山湖泊的水生生态系统可能比陆地生态系统具有更高的生态转变风险。