青藏高原末次盛冰期和全新世大暖期多年冻土边界变化的探讨

DISCUSSION ABOUT THE VARIATION OF PERMAFROST BOUNDARY IN LAST GLACIAL MAXIMUM AND HOLOCENE MEGATHERMAL, TIBETAN PLATEAU

位于中低纬的青藏高原多年冻土是第四纪高原隆升和冰期气候叠加的产物,与高纬多年冻土相比,具有厚度薄和不稳定的特点,对全球变化反应敏感.因此,评价冰期-间冰期多年冻土扩张-收缩过程和其范围重建,是研究高原环境变化的重要工作.本文依据青藏高原及周边地区温度数据和《中国冰川冻土沙漠图》,对青藏高原现代大片多年冻土、岛状多年冻土和高山多年冻土分布进行恢复.依据来自冰川、冰缘和湖泊等证据,采用末次盛冰期气温较现代低7℃,全新世大暖期气温较现代高4℃,进行末次盛冰期和全新世大暖期多年冻土分布重建.重建结果表明：末次盛冰期多年冻土扩张明显,面积约为现代冻土面积的195％;末次盛冰期大片多年冻土几乎覆盖整个高原,岛状多年冻土向东扩张明显,向西范围逐渐收缩变窄,高山多年冻土在喜马拉雅山、祁连山和横断山脉等地区扩张明显.全新世大暖期多年冻土明显收缩,面积是现代多年冻土的73％;大片多年冻土收缩幅度较小,岛状多年冻土在高原东南部收缩明显,高山多年冻土在喜马拉雅山脉、祁连山脉、横断山脉等高海拔山地发育.

This article uses meteorological data of 147 weather stations of Xinjiang, Tibet （Xizang）, Gansu, Qinghai Yunnan and Sichuan provinces from 1980 to 2010, for the analysis of the relationship between permafrost an d annual mean air temperature. Modern permafrost distribution is based on the ＂Map of The Glaciers Frozen Ground and Deserts in China＂. DEM data is from ASTER GDEM-NASA, the Coordinate System of the maps is WGS 1984. In order to establish the relationship among temperature, altitude and latitude, SPSS and EXCEL tools are applied to data regression analysis, supplementary temperature sites are added for isotherm drawing by using ArcGis tool. According to ground temperature, thickness and landforms, modern permafrost was classified into continuous permafrost, sporadic permafrost and mountainous permafrost in the plateau. The reconstruction of permafrost boundaries in the Last Glacial Maximum （LGM） and I-Iolocene Megathermal were based on the relationship between modern permafrost boundaries and modern isotherm, as well as geomorphic, sedimentary evidences, and chronological data. Summing up all the glacial, periglacial, lacustrine evidences, it is suggested that a temperature change of minus 7℃ and plus 4℃ than present are adopted to reconstructing the permafrost boundaries in the LGM and Holocene Megathermal. The result shows that the permafrost had an obvious expand in LGM, which was 195% larger than today. The continuous permafrost covered almost all the plateau. The sporadic permafrost was distinctly expanded in the eastern plateau, meanwhile, it became narrower westward. The mountainous permafrost was expanded greatly in Himalaya, Qilian Mountains and Hengduan Mountains. During the Holocene Megathermal, the permafrost had an obvious shrinkage, which was 73% smaller than today. The continuous permafrost had a slight shrinkage, while sporadic permafrost had an obvious decrease in the southeast plateau, and mountainous permafrost also had an obvious decrease, and appears in extremely high places in Himalaya, Qilian Mountains and Hengduan Mountains.