Timing of deglaciation on the northern Alpine foreland (Switzerland)

Abstract

In order to understand the forcing and the feedback mechanisms working within the climate system knowledge of the timing of cold events across the globe is necessary. This information is especially crucial for the last glacial maximum (LGM) and the subsequent deglaciation. Our approach is to directly date the classical terminal moraines of the Rhône Glacier on the northern Alpine foreland. The Rhône Glacier was the dominant piedmont glacier of the Swiss Alps during the LGM. We have analyzed four erratic blocks from the Wangen a.d. Aare region (near Solothurn) for in-situ cosmogenic 10Be, 26Al, 36Cl and 21Ne. Weighted mean ages based on all radionuclide measurements for each boulder indicate that break down of the Rhône piedmont glacier system occurred between 21.1 and 19.1 ka. The oldest age obtained, 21.1 ka from block ER 1, pinpoints the onset of deglaciation. Pull-back from the Wangen maximum position was complete by no later than 19.1 ka. Reaching of the maximum extent of the Rhône Glacier, during the last glaciation, was contemporaneous with the worldwide ice maximum between 24 and 19 ka.