中文摘要：

西藏中部是西风与季风相互作用的关键区域,对气候变化响应极为敏感。以该区域当惹雍错西北部T1阶地的沉积剖面为研究对象,利用光释光测年确立年代标尺,通过沉积物粒度、TOC、TN等代用指标分析,对当惹雍错地区中晚全新世以来的古气候变化进行研究。结果显示,T1阶地代表了约6 ka BP～1.4 ka BP期间的湖相沉积;记录了该区域中晚全新世的两个主要气候阶段。阶段Ⅰ（约6 ka BP～3.4 ka BP期间）气候温暖湿润,湖泊水位较高且稳定;阶段Ⅱ（约3.4 ka BP～1.4 ka BP）气候朝着干冷方向发展,水位下降明显,并在2.4 ka BP左右达到最低水位。通过该剖面揭示的当惹雍错中晚全新世以来的气候变化与周边区域的湖泊沉积记录进行对比,表明该地区湿度变化受季风影响较为明显;为季风在高原上的作用范围提供了证据。

英文摘要：

Westerly and monsoon are two important systems that have a reciprocal relationship. A large number of studies have shown that the East Asian monsoon gradually has shrunk back from north to south, resulting in the change of regional hydrothermal configuration in the Holocene. Central Tibet, the key region of westerly-monsoon interaction, is extremely sensible to climate changes. In this paper, a 252-cm-long profile （T1 terrace）, covering about 6-1.4 ka BP through OSL dating, was collected from northwest Tangra Yumco on the study area. Through analyzing climate of alternative indicators including grain size, total organic carbon （TOC） and the ratio of carbon and nitrogen （C/N）, the middle-late Holocene paleoclimate changes of Tangra Yumco were reconstructed. The results show that the paleoclimate in this region during middle-late Holocene experienced two major stages. In Stage Ⅰ （about 6-3.4 ka BP）, the climate was warm and wet, with a high and stable lake-level. At 6-5 ka BE the clay indicated that the climate was humid. About 5-3.4 ka BE the average grain size increased, indicating a drought trend, but the overall climate feature was still wet. In Stage Ⅱ （about 3.4-1.4 ka BP）, the climate turned cold and dry, the lake level declined obviously and reached the lowest level at 2.4 ka BE After 2.4 ka BP, the climate turned warmer before getting colder with several fluctuations. This result is almost consistent with global climate sequence and well comparable with the existing researches. The research indicates that moist degree is evidently subject to monsoon in this region, by comparison with climate changes of Tangra Yumco and surrounding records in lake sediments; however, the relationship between temperature and westerly- monsoon interaction is not obvious. Whether the warm wet-cool dry hydrothermal configuration is controlled by the Indian monsoon or the East Asian monsoon still needs further research. This paper provides some reference for further study on the interaction between the we