Quaternary glaciation in Central Asia

Thesis (Ph.D.)--University of Washington, 2018The mountain ranges in Central Asia were heavily glaciated during the Quaternary Period. The relative magnitudes of paleoglaciers varied spatially and temporally. The chronology of glacial standstills was established from 37 sites spread over nine ranges in Central Asia using cosmic-ray exposure, luminescence, and radiocarbon dating techniques, and the magnitudes of glacial standstills were estimated from equilibrium-line altitudes (ELA) of the paleoglaciers. The study sites were chosen in regions where the ELAs predicted from numerical modeling to exhibit different sensitivities to changes in air temperature and precipitation. The dating and the ELA depression from modern values (ΔELA) reveal that some paleoglaciers in humid regions advanced to their local maxima before the global Last Glacial Maximum (LGM), a period characterized by abrupt sea-level decrease and existence of large ice sheets on the continents. The glacier ELAs in these humid regions were modeled to be more sensitive to air temperatures than to precipitation. Most of the paleoglaciers advanced to their maximum during the global LGM, suggesting a strong response to minima in insolation and air temperature at the time. In cold and arid regions, most of the paleoglaciers advanced to their maximum tens of thousands of years before the global LGM, and their extents during the global LGM were limited to their cirques. In one particular case, a paleoglacier in the Mongolian Gobi advanced to its maximum during early Holocene without evidence of earlier glaciation. This spatially and temporally asynchronous glaciations in cold and arid regions were probably driven more sensitively to changes in precipitation than in air temperatures, a consistent response per the numerical sensitivity models. The results highlight the importance of precipitation in controlling the advances of paleoglaciers in a continental setting