In situ 10Be exposure ages from southeastern Norway: implications for the geometry of the Weichselian Scandinavian ice sheet

Abstract

As an initial attempt to constrain the geometry and history of the southern part of the Scandinavian ice sheet, in situ 10Be concentrations in bedrock samples have been measured from four sites in southeastern Norway. Among our results are a number of pre-Last Glacial Maximum (LGM) exposure ages. Bedrock outcrops in high elevation blockfields typically give surface exposure ages older than 20 10Be ka, whereas glacially moulded bedrock surfaces at lower elevations yield surface exposure ages younger than 15 10Be ka. These results clearly indicate the preservation of surfaces and landforms predating the LGM. Most ice-sheet models predict a thick ice mass in southeastern Norway at the LGM. Pre-LGM 10Be ages either contradict the models, supporting geomorphological reconstructions of a thin LGM ice sheet, or indicate preservation of previously exposed surfaces beneath cold-based ice. In the latter case, models of 10Be production incorporating regional glacial chronology and periodic burial suggest that the surfaces with the highest 10Be concentrations may have existed for more than one million years.