XU Liu-bing, ZHOU Shang-zhe, CUI Jian-xin, WANG Jie, David Mickelson
Plenty of glacial sediments since the earliest glaciation during the mid-Pleistocene are well preserved in the Daocheng Ice Cap area, southeastern Tibetan Plateau, where South Asian monsoon is active. Based on dating results of glacial deposits in this area using Electron Spin Resonance (ESR) and 14C techniques, combined with glacial landforms and weathering differences of tills, it is believed that there were six major glaciations in the Daocheng Ice Cap area, corresponding to MIS-16, MIS-6, mid-MIS-3, early MIS-2, global LGM and postglacial period, respectively, with gradually decreasing glaciated extents. The earliest glaciation in this area occurred at about 571.2 ka BP, which means that the southeastern part of the Tibetan Plateau was uplifted above the snow line and began to develop glaciers at least 571.2 ka BP ago, and since then this region has been significantly uplifted. Before the Holocene, the glaciers in this region had ablated away completely and they did retreat gradually with several fluctuations. A noticeable result in this study is that during the last glacial cycle, the glaciers around the Daocheng Ice Cap advanced during the mid-Megainterstadial (MIS-3b), with a considerable extent, larger than that during the global LGM. Other researchers also have drawn similar conclusions about the Quaternary glaciers in the Himalayas. From these results, it is concluded that the glacial maximum during the last glacial period may not have occurred at the same time worldwide, contrary to what has usually been assumed. During the middle MIS-3, summer insolation was lower than that in the early and the late MIS-3, but the difference in insolation between land and sea could still induce a stronger summer monsoon. It brought heavy precipitation to the glaciers in the monsoon regions. Combined with the lower temperature, the heavier precipitation was favorable for most glaciers advancing in MIS-3b. During the Last Glacial Maximum, temperature was extremely low, but the summer monsoon was considerably weaker with little precipitation, which resulted in a depression of ELA less than that during MIS-3. The result further demonstrates that no unified ice sheet occurred in the Tibetan Plateau during the Quaternary.
