GLACIAL CHRONOLOGY IN THE EASTERN TIAN SHAN, CHINA, CONSTRAINED USING COSMOGENIC 10BE SURFACE EXPOSURE DATING

Reconstructing the pattern of glacial fluctuations in the past at the confluence of major climate systems is of critical importance in understanding past climate change. Central Asia is an area where climate is affected mainly by the interaction between the westerlies and the Siberian High. However, only a few studies have been conducted in the eastern Tian Shan, China, and considerable controversy exists in the ages of dated glacial landforms/deposits due to differences in different dating techniques. Here, we present our recent work to reconstruct the timing and extent of past glaciations in the eastern Tian Shan using cosmogenic 10Be surface exposure dating. Cosmogenic 10Be minimum apparent exposure ages from six formerly glaciated valleys in the eastern Tian Shan record five major glacial advances during Marine Oxygen Isotope Stages (MIS) 6, 4, 3, 2, and 1 (the Little Ice Age; LIA). This record indicates that most glacial advances in this region correspond broadly to Northern Hemisphere climate cycles and temperature depressions, except for a MIS 3 advance that was more likely affected by precipitation changes. The evidence for glacial extent in these valleys is consistent with a hypothesis of limited ice expansions during the Last Glaciation in the Tian Shan. The LIA advance is apparently the only well-preserved glacial advance in the Holocene. Other Holocene glacial advances either never developed or were so restricted that they were destroyed by later LIA glacial advances.