Cosmogenic Nuclide-Based Boundary Conditions for Numerical Ice Sheet Models: A Simulation of the Fennoscandian Ice Sheet through A Glacial Cycle

Purdue University, West Lafayette IN

Investigators

Abstract

0138486 Harbor Major limitations in the successful use of ice sheet models for climate research arise from limited field data for model calibration. This may result in unrealistic simulations of ice sheet inception, growth, and decay, and uncertainties in reconstructing ice sheet basal boundary conditions and surface profiles. For example, trimlines and weathering differences have been interpreted as indicators of former ice sheet height in some locations, while mapping and cosmogenic nuclide-based assessment of glacial erosion patterns in Scandinavia suggest that such features in some cases represent internal thermal boundaries between wet-(warm) based erosive ice and dry-(cold) based non-erosive ice. Such radical differences in interpretation have profound impacts on reconstructed ice sheet thickness, dynamics, and extent, and paleoclimates interpretations derived from ice sheet reconstructions. The fact that uneroded areas have been identified in Scandinavia within the known limits of multiple ice sheet overriding events indicates that these uneroded areas must have survived as non-eroding (presumably frozen-bed) patches throughout ice sheet inception, growth, and decay. This observation represents a significant new constraint on basal thermal conditions for ice sheet models and is indicative of the types of constraints that field-based geomorphology and glacial geology can provide to enhance ice sheet modeling efforts. Over the past three years the Principal Investigator Arjen Stroeven, Stockholm University, and Derek Fabel, Australian National University, have worked collaboratively with support from National Science Foundation (NSF) and Swedish NSF to examine deglaciation chronology and patterns of erosion and landscape preservation in the northern Swedish mountains, the core area of the Fennoscandian Ice Sheet (FIS). The results provide the groundwork for proposing the next phase of this work, in which they will reconstruct FIS thickness, extent, and dynamics (including total ice volume-induced sea level change) over critical periods of the last glacial cycle (Marine Isotope Stage [MIS] 5d or 5b, inception phase; MIS 2, Last Glacial Maximum (LGM) phase, and; MIS 1, deglaciation phase). The paleotopography (height) of the FIS through a glacial cycle will be simulated using a state-of-the-art thermomechanical numerical ice sheet model, with key boundary conditions constrained both by cosmogenic nuclide-based reconstructions of subglacial conditions, and by an isostatic model. The team for this work has been expanded to include Alun Hubbard, University of Edinburgh, Kurt Lambeck, Australian National University, and Jens-Ove Naslund, Stockholm University, in the areas of glaciological and isostatic modeling. New reconstructions will likely have wide significance, both to European ice sheet and paleoclimate reconstructions and evaluations of evidence of sea level low-stands (proxy for total land-based ice on earth) and also in encouraging re-evaluation of the dynamics of inception, growth, and decay of other major ice sheets worldwide.