Unrealistic simulation of ice sheet inception and decay in mountainous regions, uncertainties in reconstructing ice surface profiles, and common failure to consider landscape development under ice sheets all contribute to major limitations for successful use of ice sheet models in climate research. For example, trimlines and weathering differences have been interpreted as indicators of former ice sheet height, but recent mapping in Scandinavia suggests that such features may reflect internal thermal boundaries between wet-(warm)-based erosive ice and dry-(cold) based-non-erosive ice, leading to very different interpretations of ice sheet thickness and height. The Principal Investigators will attempt to resolve conflicting glacial landform interpretations for parts of the Fennoscandian ice sheet. Geomorphologic and stratigraphic evidence indicates the Norwegian-Swedish mountains are an important area for understanding Fennoscandian ice sheet inception and decay. Glacial morphology in this mountain range reflects cirque glacier, valley glacier, and ice sheet erosion at different times and with various intensities over the past six million years. The oldest preserved surface is a potential reference horizon against which glacial erosion can be computed to enhance our understanding of ice sheet dynamics. This is critical groundwork for enhanced model simulations of the glacial cycle, which would test for general circulation models in predicting climate. This work will be accomplished by measuring multiple cosmogenic radionuclides in samples collected from rock surfaces in distinct, recently mapped, geomorphic regions. The results will test existing hypotheses of ice sheet configuration and provide new information for debates over the age of "preglacial" surfaces that appear to have survived repeated ice sheet overriding. The height of the Weichselian ice sheet and the spatial patterns of basal thermal regimes and associated glacial erosion of the Fennoscandian ice sheet will be studied. Insight into landscape development and basal thermal regimes will provide new boundary conditions for Fennoscandian ice sheet modeling being undertaken by Swedish scientists. The Principal Investigators will field test whether a surface has experienced lengthy ice burial with a new application of cosmogenic radionuclides. To be successful, the Principal Investigators will collect samples from sites within landscapes of different types of glacial histories. The Swedish Natural Science Research Council has funded the Principal Investigators' Swedish counterparts for similar work and the two groups will work collaboratively on this project. Recognition of suitable landscape features relies on high quality mapping of mountain geomorphology which is a primary area of expertise of the Paleoglaciology Group at the University of Stockholm. Purdue University facility and facilities will provide expertise and analytical capabilities in glacial geomorphology and applications of cosmogenic radionuclide techniques.
