Jungquartäre Vergletscherung und Paläoklimatologie der hochkontinentalen Gebirge des mongolischen Altai und Khangai
Final Report Abstract
Over the last decade, an increasing number of studies from mountain regions in High Asia have shown that late Pleistocene glacial timings differed significantly across this vast region, with important implications for paleoglaciological reconstructions and the understanding of Central Asia's climatic evolution. Using a combination of geomorphological mapping, 10Be surface-exposure-dating of glacial landforms (109 CRN ages), and glacial mass balance / ice flow modeling, this research project generated important new information on the Pleistocene paleoglaciation of the Altai and Khangai Mountains of Mongolia. The investigated areas (seven formerly glaciated valley systems) were located along an 800 km E-W transect from the central Mongolian Khangai to the Turgen-Harhiraa and Tsengel-Harhiraa Mountains in the Mongolian Altai. The resulting geochronological records show that the largest late Pleistocene ice advances in this region occurred during MIS-5 (i.e. late MIS-5 to early MIS-4 transition), despite earlier suggestions by previous studies that the maximum advance occurred during the coldest periods of the last glacial cycle (i.e. MIS 4 or MIS 2). Furthermore, data from the Khangai Mountains demonstrate that this region also experienced a major glaciation between 40 - 30 ka during MIS-3, which exceeded the ice limits set during the subsequent MIS-2 advances. In contrast, we find no evidence for a major MIS-3 glaciation (reaching or exceeding the MIS-2 limits) in the investigated areas of the Mongolian Altai. After MIS-2, glacial retreat across Mongolia commenced at about 19 ka, but large glaciers, as indicated by ice positions located only 2-3 km upvalley from the max. MIS-2 limits, survived in most valleys until about 16 ka. After about 15 ka, glaciers retreated rapidly into the valley headwaters with multiple sites showing that glaciation in most parts of the Khangai and Altai was reduced to the mountain cirques (or had disappeared altogether) by ca. 13 ka. To study the responsiveness of the investigated glacier systems to climatic change, a coupled 2D surface energy balance and ice flow model was used to determine steady-state conditions for glaciers under various climatic scenarios. Using this model, different temperature and precipitation settings were tested, which would produce glacier configurations (downvalley extent and ice thickness) that matched the previously field-mapped and 10Be-dated ice limits. The modeling results suggest that temperatures during the MIS-3 ice advances in the Khangai Mountains were -4.4 to -5.3°C lower than today, with a modeled precipitation range from 125-75 % of the current annual total. This setting, characterized by a cool-wet climate with a greater-than-today contribution from winter precipitation, and an additional input of recycled moisture from the expanded paleo-lakes in the Valley of the Great Lakes, generated a highly favorable setting for major glaciation in central Mongolia. Yet, glacial accumulation also responded positively to the far colder and drier conditions of MIS-2. For the MIS 2 ice advances the modeling results suggest a temperature depression of -4.6 to -5.7°C (P between 50 to 25% of the modern total) in the East-Turgen study area, and between -6.6 to 7.5°C (P = 50 - 25%) in the Khangai Mountains. These results document a 1.8 - 2.0 °C difference of the modeled temperatures required to expand the studied paleo-glaciers in the Turgen and Khangai mountains to their field-mapped MIS 2 ice limits, highlighting a spatially differentiated pattern of paleo-temperature lowering across the studied 800 km NW-SE transect. The lack of a severe cooling during the MIS 3 ice advances, and probably also during the late MIS 5 ice expansion, suggests that variations in atmospheric circulation patterns, which are significant for controlling the regional precipitation/moisture supply, were a key driver for the reconstructed late Pleistocene ice advances. This notwithstanding, there is also clear evidence for an extensive glaciation during MIS-2, coinciding with a period of severe cooling and hyperarid conditions in Mongolia. This highlights that glacier systems in Mongolia responded sensitively, both, to variations in moisture supply and its seasonal distribution, and to the insolation minima of the last glacial cycle. Viewed in context of other Pleistocene glacial and paleoclimatic records from High Asia, these results reveal a transitional pattern of glaciation, with glacial records from central Mongolia (Khangai) sharing features with those from southern Central Asia and NE-Tibet (i.e. large ice advances during interstadial wet phases) while the records from the Altai Mountains in NW-Mongolia (i.e. major ice expansion during the MIS-4/MIS-2 insolation minima) are more in tune with glacier responses known from Siberia and western Central Asia.
Publications
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(2012). Late Quaternary glacial history of the Otgon Tenger area (Khangai Mountains, central Mongolia) based on cosmogenic 10Be exposure dating. International Symposium on Biodiversity Research in Mongolia, March 2012, Halle
Rother, H., Lehmkuhl, L., Fink, D., Nottebaum, V.
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(2014). Alter und Ausdehnung der eiszeitlichen Vergletscherung in der Mongolei. Festschrift zum 20. Jubiläum mongolisch-deutscher geowissenschaftlicher Zusammenarbeit. Botschaft der Bundesrepublik Deutschland in der Mongolai, Ulaanbaatar, S. 114-121
Rother, H.
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(2014). Surface exposure dating reveals MIS-3 glacial maximum in the Khangai Mountains of Mongolia. Quaternary Research 82: 297-308
Rother, H., Lehmkuhl, F., Fink, D., Nottebaum, V.
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(2015). Holocene and late Pleistocene glacier fluctuations in Mongolia. International Symposium on Glaciology in High-Mountain Asia, International Glaciological Society, March 2015, Kathmandu, Nepal
Lehmkuhl, F., Klinge, M., Pötsch, S. ,Rother, H., Hülle, D.
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(2015). MIS-3 interstadial ice expansion in the Khangai and Altai Mountains of Mongolia: insights into chronology and climatic forcing. XIX INQUA Conference. August, 2015, Nagoya, Japan
Rother, H., Pötsch, S., Lehmkuhl, F.
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(2015). Timing and modeling of late Pleistocene glaciations of selected valleys in central and western Mongolia. Volkswagen Symposium on Landscape Evolution Modeling, Hannover
Pötsch, S., Rother, H.
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(2015). Timing of late Pleistocene glaciation in Mongolia: Surface exposure dating reveals a differentiated pattern of glacial forcing, European Geoscience Union EGU Meeting, April 2015, Vienna Austria
Pötsch, S., Rother, H., Lorenz, S., Walther, M., Lehmkuhl, F.
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(2016). Distribution and timing of Holocene and Pleistocene glacier fluctuations in western Mongolia. Annals of Glaciology 57 (71): 1-10
Lehmkuhl, F., Klinge, M., Rother, H., Hülle, D.
