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Evolution of the Cryosphere in the Tibetan Plateau, China, and its Relationship with the Global Change in the Mid Quaternary

SHI Ya-Feng (Lanzhou Institute of Glaciology and Geocryology, Chinese Academy of Sciences, Lanzhou 730000)  
This paper defines the implication and composition of the cryosphere and presents the process of the cryospheric evolution in a very long period from the appearance of ice cover in Antarctic about 42 Ma ago to the mid Pleistocene During the early Pleistocene, there were only a few peaks of glaciation occurred in the Himalayas Until the orogenic movement of Kun-huang from 1 1 to 0 6 Ma BP, the plateau ground lifted up to about 3 500 m, resulting in the plateau's cooling; and at the same time, the control of the earth orbit taking in solar insolation changed from the orbital incline rate of 41 ka in a cycle to the eccentricity of 100 ka in a cycle, concomitantly resulting in the Plateau's cooling as well Because the events mentioned above were coupled, the third glaciation from the last or the maximum glaciation occurred in 0 6 to 0 8 Ma BP The period when the maximum glaciation occurred was comparable with MIS16 Period, with the total glacier area more than 5×10 5 km 2 Air temperature in summer at the equilibrium line of glaciers was 1~2℃ higher than that at present Precipitation in four mountainous areas of the mid and east plateau was 1 8~3 2 times as much as that at present, while precipitation in the arid West Kunlun Mountains was only 30% more than the present one Permafrost grew at a large scale in the west plateau and stable snow cover existed with different depths in the plateau, except for summer Consequently, the albedo was greatly increased on one hand and the snow melting consumed a large amount of heat energy on the other hand, resulting in the plateau's effect changing from a heat source of a year-round to a cold source of most months in a year and furthermore resulting in a decrease in air temperature The winter monsoon to the outside was enhanced and as a result, summer precipitation from the southwest monsoon decreased However, precipitation was still rich and climate was relatively cool and humid in the mid and east plateau where climate constantly affected by the south branch of the west jet stream and by the hot low in summer, which in turn had an important impact on climate of the plateau itself and its nearby areas The interglacial between the last but one and the last but two glaciations was symbolized by MIS13 period During the interglacial, climate was much warmer than that in glaciation Forestry was distributed near what is now called Qinghai-Xizang Highway and the laterite crust of weathering grew in the south plateau The plateau's role as a heat source was strengthened, resulting in an enhancement of summer monsoon Except for existence of a small number of high-elevation glaciers, such as the Guliya Glacier, a large part of glaciers and permafrost areas might be fully depleted and disappeared
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