Speaker
Description
The Tibetan Plateau and its surrounding mountains (TPSM) has experienced glacier expansion during the Global Last Glacial Maximum and punctuated retreat during the following deglaciation. Preserved moraines provide a reliable record for glacier extent and their terrestrial cosmogenic exposure dating marks the transition of glacial advance or stasis to one of recession. As a wide geographic domain, when and how the glaciers retreated on the TPSM during the last termination remains unclear. In order to investigate this issue, we recalculated 1077 boulder 10Be exposure ages from 239 moraines spanning the period of 26.5-10 ka ago using the LSDn scaling model and the Probabilistic Cosmogenic Age Analysis Tool. We divided the TPSM into seven regions and utilized the kernel density estimate method to calculate the summed probability distribution of moraine ages and compared the peaks to identify phases of glacier activities for these regions. The results show that the initiation of glacier retreat on TPSM began synchronously at ca 22 ka, aligning with worldwide glacier retreat in response to the onset of summer insolation rise on the mid-latitude Northern Hemisphere. Phases of moraine abandonment concentrated at five peak stages, i.e., 22-20 ka, 19-18 ka, 17-16 ka, 14.5-12.9 ka and 11.6-10 ka, broadly corresponding to the periods of thousand-year enrichment of δ18O from the Greenland ice core. Synchronous retreat over the entire TPSM occurred at 22-20 ka, 19-18 ka, 14.5-12.9 ka. Asynchronous retreat at 17-16 ka was not observed in Pamir and NE Tibet, which is likely a result of the sustained influence of the Westerlies over these regions. An exposure age peak at 11.6-10 ka data was absent on Central Tibet, NE Tibet and Tianshan, which is likely a bias due to the lack of chronology for the remote and perched moraines in these regions. We suggest that 17-16 ka was a major adjustment in atmospheric circulation from glacial to interglacial state over the TPSM.
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