9726185 Lehman The goal of the proposed work is to constrain models of the Fennoscandian ice sheet (FIS) during the last glacial maximum (LGM) and subsequent deglaciation by applying techniques of surface exposure chronology using cosmogenic nuclides. A large body of field work in the high mountains of Norway documents high altitude glacial trimlines and areas of deeply weathered bedrock that have a regionally consistent configuration, suggesting that they may demark the vertical limit of the FIS. However, profiles based on the spatial distribution of these features differ significantly from profiles of ice sheet elevation derived from various numerical and conceptual ice sheet reconstructions (for example, ICE-4G and CLIMAP). Although it is clear that one of the two general approaches to reconstructing the FIS is flawed, it is difficult to say which one, primarily because the geomorphic features under debate have not been dated. Our prior work in the mountains of western Norway demonstrate that such dating is, indeed, feasible. The proposed work will produce the first numerical chronology for these features, thereby permitting us to assess the validity of various ice sheet reconstructions for the region, and, by inference, in North America (e.g. for the Laurentide ice sheet). As the CLIMAP and ICE-4G reconstructions have been widely adopted as boundary conditions in simulations of LGM climate using atmospheric general circulation models, our studies will also bear on the efficacy of those modeling results and related assessments of climate sensitivity. In addition, the proposed work will address a fundamental problem in glacial geology that of interpretation of weathering zones in formerly glaciated regions of the Northern Hemisphere.
