青藏高原及周边地区MIS 3中期冰进探讨

GLACIAL ADVANCE IN THE QINGHAI-TIBET PLATEAU AND PERIPHERAL MOUNTAINS DURING THE MID-MIS 3

随着ESR,OSL以及CRN等新技术被应用到第四纪冰川测年,青藏高原及周边山地的许多地区建立起了第四纪冰川演化的年代序列,研究人员在青藏高原南缘和东缘发现末次冰期最大规模古冰川作用出现于末次冰期的间冰阶(MIS 3),而不是末次冰期晚阶段(MIS 2)。对该区域内已获得的测年资料进行总结,发现在兴都库什山、喜马拉雅山、昆仑山、念青唐古拉山、唐古拉山、喀喇昆仑山、横断山、祁连山、天山、帕米尔高原以及台湾山地等(共30个点)都存在MIS 3山地冰川前进的年代数据,其中,虽有部分点的数据精度和可靠性不高,但不可否认青藏高原及周边山地曾发生MIS 3山地冰川前进的事实,且多数年代数据都集中于MIS 3中期。通过年代学资料与古环境记录的综合分析,笔者初步得出:在季风环流控制区,MIS 3(中期)冰进可能是由于该阶段中期的冷期(也可能是古里雅冰芯记录中47～43kaB.P.两次冷事件的直接作用)结合较丰富的亚洲季风降水造成;在西风环流主要控制区,如天山、帕米尔地区与西昆仑山,虽然在MIS 3时由于冰盖退缩,高纬度的冷高压减弱,使得西风急流北支北撤,西风强度有所减弱,但相对LGM时大洋的温度还是较高,蒸发旺盛,因而西风环流可为上述地区带来较多的降水,配合MIS 3中期的低温致使冰川前进。用多种技术方法交叉对冰川遗迹进行系统定年,是现阶段第四纪冰川研究面临的重要内容,还应注意季风与西风气候系统下冰川演化模式可能存在的异同。

In recent years, dating techniques, including CRN （ cosmogenic radionuclide） , OSL （ optically stimulated luminescence） and ESR （electron spin resonance） , which can potentially determine the ages of glacial landforms and sediments,have been refined and applied widely. This paper reviewed dating results in the Tibet Plateau and peripheral mountains. It was found that the local last glacial maximum（LGML） in Himalaya and south Eastern Tibet Plateau occurred in MIS 3 （58 - 32kaB. P. ） （ especial in mid-MIS 3 or 54 - 44kaB. P. ） rather than in the global Last Glacial Maximum（LGMG or 25 -15kaB. P. ） of MIS 2. Moreover,MIS 3 glacial advances happened in about 30 areas in Central Asia, including Hindu Kush Mountains, Himalaya Mountians, Kunlun Mountians, Nyainqentanglha Mountains, Tanggula Mountains, Karakorum Mountians, Hengduan Mountians, Qilian Mountains, Tianshan range, Pamir Plateau, and in high mountains of Taiwan. In combination with the available records of palaeoclimate,it can be preliminarily concluded that in Asia monsoon circulation areas,the cold period in mid-MIS 3 and abundant precipitation carried by the strong Asia monsoon caused glacial advances. And in westerly circulation areas, although the retreating of ice sheet caused the cold anticyclone weakening in high latitude areas so that the north branch of the westerly retreated northward and weakened, the sea surface temperature was higher than that of LGM, and the evaporation was large. Therefore, the precipitation was still abundant in westerly circulation areas. With the low temperature in mid-MIS 3, glaciers advances occurred in Tianshan Mountains, Pamir Plateau and Western Kunlun Mountains.