An early advance of glaciers on Mount Akda?, SW Turkey, before the global Last Glacial Maximum; insights from cosmogenic nuclides and glacier modeling

摘要

For the first time in Turkey, we report an early advance of glaciers before the broadly defined global Last Glacial Maximum (LGM). Forty-one moraine boulders from three glacial valleys on Mount Akda? (36.54°N, 29.57°E, 3016 m), southwest coast of Turkey, were dated with cosmogenic ~(36)Cl. Valleys on the north side of the mountain were filled with few km long glaciers that terminated at elevations of about 2000 m above sea level (a.s.l). The pre-LGM glaciations reached their maximum positions (2150 m a.s.l) by 35.1 ± 2.5 ka ago (1σ; ka = 1000 calendar years). The glaciers readvanced during the global LGM and reached their farthest locations (2050 m a.s.l) by around 21.7 ± 1.2 ka ago. Later, glaciers retreated and shortly stabilized during the Lateglacial at around 15.1 ± 0.9 ka ago. Using the glacier modeling and paleoclimate proxies from the Eastern Mediterranean, we estimated that if temperatures during the LGM were 8-11 ℃ colder than modern, which is suggested by paleotemperature proxies from the region, precipitation was up to two times more than that of today. Previous estimates on southwest coast of Turkey indicate a similar precipitation value while central Turkey requires drier conditions, implying regional heterogeneity on LGM climates in Turkey.