Glacial advances in southeastern Tibet during late Quaternary and their implications for climatic changes

摘要

Southeastern Tibet is the type area for monsoonal maritime glaciers in the Qinghai-Tibet Plateau with more than 4000 mountain glaciers covering an area of approximately 8000 km~2. Based on moraines in the Boduizangbo River Valley, glacial advances have been recognized for the Guxiang, Baiyu, and Yuren Glaciations. Cosmogenic radionuclide surface exposure, ESR, and radiocarbon dating methods are used to estimate moraine ages. The dates suggest that glacial advances occurred during MIS-6, MIS-2 and MIS-1. Moraines of possible MIS-4 or MIS-3 age are also present, but have not yet been dated. During the Guxiang Glaciation, glaciers converged in the Boduizangbo Valley and formed a glacier approximately 100 km long, reaching the Parlongzangbo River Valley. During the Baiyu Glaciation the glacier was about 80 km long, yet did not reach the main valley of the Parlongzangbo River. During the Yuren Glaciation, glaciers advanced only within tributary valleys feeding the Boduizangbo River. Based on glacier extent, reconstructed equilibrium line altitudes during the Guxiang and Baiyu Glaciations were approximately 800 m and 600 m lower, respectively than at present. Mean annual air temperatures were depressed by approximately 6.6-7.8 ℃ compared to present values, estimating a 40% decrease in precipitation during glaciations.