Quaternary glaciation of Muztag Ata and Kongur Shan:Evidence for glacier response to rapid climate changes throughout the Late Glacial and Holocene in westernmost Tibet

摘要

The glacial geology of two massifs,Muztag Ata and Kongur Shan,in western Tibet was examined to help define the timing and style of glaciation in the semiarid regions of western Tibet Remote sensing,geomorphic mapping,and ~(10)Be terrestrial cosmogenic nuclide(TCN)surface-exposure dating of boulders on the moraines and sediment in depth profiles show that glaciers advanced at least 12 times during at least the last two glacial cycles.Over this time,the style of glaciation changed progressively from one that produced ice caps to one that produced less extensive and more deeply entrenched valley glaciers.The timing of the two earliest glaciations is poorly defined,but they likely occurred prior to the penultimate glacial cycle(the Karasu glacial stage)and the early part of the last glacial cycle or during the penultimate glacial cycle(the Subaxh glacial stage).In contrast,the timing of later glacial advances(the Olimde glacial stage)is relatively well denned showing quasiperiodi-cal oscillations on millennial time scales(17.1 ± 0.3 ka,13.7 ± 0.5 ka,11.2 ± 0.1 ka,10.2 ± 0.3 ka,8.4 ± 0.4 ka,6.7 ± 0.2 ka,4.2 ± 0.3 ka,3.3 ± 0.6 ka,1.4 ± 0.1 ka,and a few hundred years before the present).These data suggest that since the global Last Glacial Maximum(LGM),the glaciers in western Tibet likely responded to Northern Hemisphere climate oscillations(rapid climate changes),with minor influences from the south Asian monsoon.This study provides the first well-defined glacial geologic evidence to suggest that glaciers in western Tibet respond to rapid climate changes on millennial time scales throughout the Late Glacial and Holocene.