末次冰盛期以来青藏高原西北部阿克赛钦湖古水热变化及对气候的响应

The Tibetan Plateau (TP) is influenced by the northern hemispheric middle latitude Westerlies and the Indian Summer Monsoon (ISM). The climate of the TP then shows significantly spatial-temporal differences. For better understanding the present climatic processes and the future trends of the TP, it is necessary to carry out research on the historical changes in the Westerlies and ISM and the interplay between of them. The present climate of the northwestern TP is mainly controlled by the Westerlies; however, the ISM probably greatly affected the climate of the region during the warm periods of the past. Therefore, the northwestern TP is an ideal site to research on the changes in the Westerlies and ISM. This project proposed to drill a long core which should extend to the Last Glacial Maximum (LGM) from Lake Aksayqin, a typical lake on the northwestern TP. Based on the precise chronology frame of the sediment core, the high resolution paleohydrology and paleotemperature variations of the lake basin since the LGM will be reconstructed using compound-specific hydrogen isotope ratios (δD) of sedimentary n-alkane and glycerol dialkyl glycerol tetraethers (GDGTs), respectively, as well as commonly used proxies such as grain-size, total organic carbon (TOC), total nitrogen (TN) and C/N ratios. For further understanding the interplay between Westerlies and ISM and the mechanisms on the northwestern TP since LGM, the reconstructed results of the lake will be compared with those high quality records in the typical regions of ISM dominated, Westerlies dominated and the transitional zones between of them. This project will deepen the knowledge of the interplay between of the Westerlies and ISM on the TP since the LGM.

青藏高原受中纬西风和印度夏季风两大环流系统影响，区域气候变化因此具有显著时空差异。开展历史时期西风和季风大气环流变化及相互作用的研究，是深入认识青藏高原不同地区当前气候变化过程及其未来变化趋势的必然途径。青藏高原西北部现今受西风环流显著影响，然而在历史温暖时期也可能受到季风的显著影响，因此是开展历史时期西风与季风环流变化的理想地点。本项目拟选取高原西北部典型湖泊阿克赛钦湖超越末次冰盛期的沉积长岩芯为研究对象，在剔除碳库效应和建立精确的年代序列基础上，利用正构烷烃和GDGTs为主要指标，以常规指标作为辅助，重建青藏高原西北部末次冰盛期以来的高分辨区域古水文和古温度变化历史，并与青藏高原内部以及周边典型季风区和典型西风区古气候记录进行对比，揭示青藏高原西北部末次冰盛期以来不同时段西风和季风环流变化及其驱动机制。本项目研究成果将为揭示青藏高原西风和季风环流相互作用过程提供重要参考资料和理论依据。

开展青藏高原西部古水热气候变化重建研究，是理解青藏高原西风与季风大气环流变化及相互作用过程的有效手段，也是深入认识青藏高原当前气候变化过程及其未来变化趋势的必然途径。本项目利用青藏高原西部典型湖泊阿克赛钦湖和玛旁雍错两个湖泊的沉积岩芯，开展了青藏高原西部过去不同时间尺度的气候变化重建以及驱动机制分析工作。本项目利用多指标重建了阿克赛钦湖过去不同沉积深度条件下的湖泊水动力及其环境变化过程；利用生物标志化合物指标重建了玛旁雍错晚冰期以来的干湿变化历史；研究发现玛旁雍错晚冰期区域气候湿润，可能反映晚冰期高原气候逐渐暖湿化的普遍特点，推测是晚冰期北半球太阳辐射量增高、同时印度夏季风开始持续加强的结果；玛旁雍错流域早全新世区域气候湿润、中全新世以来干旱化显著，反映玛旁雍错流域及青藏高原西部地区全新世以来区域干湿变化主要受印度夏季风气候系统控制。在本项目支持下，项目负责人还开展了长江中下游典型湖泊升金湖过去千年以来的高分辨率气候变化重建与驱动机制分析工作；研究发现该地区过去千年以来的气候变化不仅受东亚夏季风气候系统控制，同时还受到ENSO状态及太阳辐照度变化等因素显著影响，具体表现在：在中世纪暖期和小冰期后期，以拉尼娜态为主，太阳辐照度较强，升金湖地区气候较为干旱；小冰期前期和现代暖期以厄尔尼诺态为主，升金湖地区气候较为湿润；而在现代暖期后，升金湖地区气候变化与太阳辐照度关系不明显，推测可能受人类活动影响更为强烈。