Dating the onset of LGM ice surface lowering in the High Alps

The general chronological outline of the Last Glacial Maximum (LGM) in the Alps is well known after more than two centuries of ice age research in Europe. Current studies focus on resolving the details of the deglaciation process after the LGM. Particularly few data in this context are available from the High Alps. Here we report chronological constraints on the onset of deglaciation in two different study areas from the Western and Eastern Alps: the Mont Blanc (Italy) and Zillertal Alps (Austria). We sampled 32 bedrock and boulder surfaces from high elevation ridges beneath the glacial trimline. The oldest Be-10 exposure ages of similar to 18.5 ka correspond to the initiation of lowering of the LGM ice surface. Identical ages from both study areas suggest synchronous decay of the LGM glaciers in the accumulation zones of the Western and Eastern Alps. Thus, the High Alpine ice surface lowered roughly synchronously to the downwasting of the glacier tongues in the forelands that was completed 19-18 ka. In both study areas, ages of numerous samples that are consistently 2-3 ka younger than 18.5 ka suggest the persistance of remnant ice patches at high elevations in the Lateglacial accumulation zones approximately until the Bolling-Allerod interstadial. (C) 2016 Elsevier Ltd. All rights reserved.