TIMING AND STYLE OF GLACIATION THROUGHOUT THE HIMALAYA AND TIBET DURING THE LAST GLACIAL-INTERGLACIAL TRANSITION

Tibet and the bordering mountains are the most extensively glaciated tract outside the polar regions, exerting an important influence on regional and global environmental change. Glaciation in this region is controlled by two major climatic systems: the mid-latitude westerlies and the South Asian monsoon. In addition, significant interannual climatic variability in the region is associated with El Nino-Southern Oscillation. Furthermore, glaciation is strongly influenced by topographic constraints. The glacial system provides water for hundreds of millions of people in central Asia, and variations in the glacial and associated hydrological systems have profound socio-economic and political consequences. Yet despite the regional and global importance of glaciation in High Asia, the dynamics, extent and timing of Late Quaternary glaciation in this region are poorly understood and defined. This is particularly so for the last glacial-interglacial transition. To examine the nature of glacier oscillations, key areas throughout the Himalaya and Tibet were studied using glacial geomorphic mapping, sedimentology, and cosmogenic radionuclide (CRN) surface exposure and optically stimulated luminescence (OSL) dating techniques to define the timing and extent of Late Quaternary glaciation. These studies show a strong monsoonal influence on glaciation, synchroneity of glaciation throughout the region and strong topographic constraints on extent of glaciation. Furthermore, it is evident that glaciation was restricted in extent during the global Last Glacial Maximum (LGM), contrasting with extensive advances during insolation maximum in early part of the last glacial cycle. Nevertheless, notable glacial advances occurred during latter part of the LGM (~15-16 ka), the Lateglacial Interstadial, and the early Holocene. These glacial advances were most extensive in the monsoon-influenced regions and may have even been more extensive than the LGM advance. The results suggest that glaciation throughout Tibet and the Himalaya is controlled by precipitation changes related to oscillations in the southwest Asian monsoonal system combined with cooling that is broadly coincident with the global cooling cycles.