Glacial Geomorphology and Ice Ages in Tibet and surrounding mountains

Evidence for an ice sheet covering Tibet during the Last Glacial Maximum (LGM: stage 3-2) means a radical rethinking about glaciation in the Northern Hemisphere. The ice sheet’s subtropical latitude, vast size (2.4 million km2) and high elevation (∼6000 m asl) (Figure 2) caused a substantial, albedo-induced cooling of the Earth’s atmosphere and the disruption of summer monsoon circulation. The uplift of Tibet and the reaching of specific threshold values of plateau elevation being synchronous with the onset of the ice ages at ∼2.8 Ma B.P. and their intensification from ∼1 Ma B.P. onwards, a causal link between these factors seems likely. During 35 campaigns of field investigations (Figure 1), the ice-age inland glaciation of Tibet has been reconstructed on the basis of classical glacigenic forms of erosion and accumulation as well as on its accompanying sediments and the arrangement of the positions. Absolute datings obtained by different methods classify this glaciation as being from the LGM. With the help of 13 climate measuring stations, radiation and radiation balance measurements have been carried out between 3300 and 6650 m asl in Tibet. They indicate that the subtropical global radiation reaches its highest energies on the High Plateau, thus making Tibet today’s most important heating surface of the atmosphere. At glacial times 70% of those energies were reflected into space by the snow and firn of the 2.4 million km2 extended glacier area covering the upland. As a result, 32% of the entire global cooling during the ice ages, determined by the albedo, was brought about by this area– now the most significant cooling surface. The uplift of Tibet to a high altitude about 2.8 Ma ago, coincides with the commencement of the Quaternary Ice Ages. When the Plateau was lifted above the snowline (=ELA) and glaciated, this cooling effect gave rise to the global depression of the snowline and to the first Ice Age. The interglacial periods are explained by the glacial-isostatic lowering of Tibet by 650 m, having the effect that the initial Tibet ice, which had evoked the build-up of the much more extended lowland ices, could completely melt away in a period of positive radiation anomalies. The next ice age begins, when – because of the glacial-isostatic reveres uplift – the surface of the Plateau has again reached the snowline. This explains, why