LATE QUATERNARY GLACIER AND LAKE LEVEL VARIATIONS IN MONGOLIA AND BORDERING REGIONS

The current state of research concerning the extent of Late Pleistocene ice and lake level variations for Western Mongolia and bordering regions is summarized. This includes also a review of pervious work in Mongolia and adjacent regions to produce a better understanding and reconstruction of past regional climatic and environmental conditions. To show the variations in the ice extent, the modern and Late Pleistocene equilibrium-line altitudes (ELAs) for this area are presented in two cross-sections. The ELAs are relatively low in the more humid outermost ranges of the arid and semiarid regions of Central Asia and are rising towards the central part of Mongolia. The limited extent of present and Pleistocene glaciers in the eastern part of the Russian Altai and in the Mongolian Altai is the result of reduced precipitation from west to east. This results in a rise of present and Pleistocene ELAs towards the east. A similar situation can be observed for northern margin of the Tibetan Plateau. However, in both areas this was more pronounced during the Pleistocene than today. There is an essential lack of absolute dating in this particular region. However, from present knowledge, most Late Pleistocene glacier advances take place in the MIS 2 and 4. Recent data from the Russian Altai suggest a main glacier advance between 20 and 28 ka.

Mongolian lake levels experienced major changes during the Late Quaternary. Absolute high stands occurred during the Early to Mid-Pleistocene. Scattered evidence points to a transgressive phase at the end of MIS 5. Relative high stands are well documented for the MIS 3 and the Early to Mid-Holocene times, in some areas the latter period starts already in Late-glacial time. The Last Glacial maximum (MIS 2) appears to be a dry period including low lake levels and the development of dune fields. These lake level variations in Mongolia and the surrounding areas coincide with high lake levels in other parts of Central Asia, e.g. in western Tibet or western China. Contrary to the overall pattern of lake level trends, some lakes exhibit a different or even opposite behaviour, which is dependent on local factors controlling the hydrological regime.