藏东南然乌地区古冰前湖沉积记录的末次冰期冰川与气候变化研究

The last glacial period, when climate changed dramatically, is important for studying how glaciers respond to climate change, but the patterns and mechanisms of glacier variation on the Tibetan Plateau are still controversial. Glacial geomorphology is the most direct way for reconstructing paleoglacier variations, but it is incontinuous and is easy to be eroded or reworked. Glacial lakes can receive both the glacial eroded rocks and the soil organic matters and plant fragments, thus their sediments can record continuous changes of glacier and climate. This study will use a set of high-stand sediments of a proglacial lake in the Ranwu region, southeastern Tibet, to obtain continuous and high-resolution records of glacier, temperature and precipitation during the last glacial period. Radiocarbon and OSL dating methods will be combined to obtain sediment ages. We use grainsize, branched GDGTs, hydrogen isotope of n-alkanes and other proxies to reconstruct last glacial glacier, temperature and precipitation changes. Based on mutiproxy comparison and regional comparison, we try to reveal the response patterns of the glacier in this region to climatic forcings, especially the forcing of the millennial scale climate change events. Using proglacial sediments to study the response of glaciers to climate change, this study will be important for predicting future glacier and water resources changes.

末次冰期气候变化剧烈，是研究冰川如何响应气候变化的重要时段，然而目前青藏高原末次冰期冰川变化模式及机制还存争议。冰川地貌是重建古冰川的最直接手段，但通常不连续且容易被侵蚀改造。冰前湖通常可以同时接收冰川侵蚀的大量岩石碎屑和流域内土壤有机质和植物碎屑，因此其可以同时记录连续的古冰川、古气候信息。本项目选择藏东南然乌地区一套厚32.5米的末次冰期高沉积速率的古冰前湖沉积为研究对象，多测年手段（光释光、14C）结合定年，开展同一剖面古冰川（粒度、元素等指标）、古温度（土壤细菌bGDGTs相关指标）、古降水（陆生植物长链正构烷烃单体氢同位素）多指标分析，获取末次冰期高分辨率连续的古冰川、古气候记录，讨论冰川对温度、降水变化的敏感性，探讨区域冰川及气候对全球气候变化（特别是千年尺度气候突变事件）的响应方式及机制。本项目利用冰前湖沉积研究冰川如何响应气候变化，对于预测未来冰川及水资源变化有重要意义。

项目负责人系统开展了现代冰前湖沉积物的沉积特征研究，揭示冰川侵蚀源的较细的粘土和细粉砂可以作为冰川侵蚀和融水强度的指标，为然乌古湖相地层研究奠定基础。开展了然乌古湖相沉积地层研究工作，并在剖面处进行了陆地钻探，获得综合岩芯长达90米，这是藏东南地区目前最长的高分辨率湖相沉积物岩芯。初步建立古湖相地层上部剖面的年龄与深度模型，通过粒度、磁化率等多指标分析，揭示末次冰期期间，该地区冰川存在多次千年尺度的剧烈波动，这可能与全球末次冰期期间气候不稳定性有关。