| Summary: | The dynamic behaviour of the Antarctic ice sheet is controlled by both creep deformation and theoccurrence of sliding at the base of the ice sheet. The activity of these processes is highly temperaturedependent and as such they are influenced by the geothermal heat flux at the ice-solid Earth interface. The constitutive relation describing the rate of ice deformation in numerical ice sheet models is typicallya power-law relationship between the stresses driving the flow and the corresponding strain rates, witha separate term describing the temperature dependence. Many models use a simplified prescription ofthe temperature dependence which does not adequately describe the sensitivity of deformation rates totemperature within ~5C of the melting point. This leads to an underestimation of strain rates in thewarmest ice. While the increased sensitivity of deformation rates to temperature near the melting point is clearlydemonstrated by laboratory experiments, it is constrained by a relatively small number of observationsdue to the inherent difficulties in conducting experiments at high temperatures. Here we presentpreliminary results from an experimental program designed to improve the constraint on deformationrates at temperatures close to the melting point. Simple shear deformation experiments wereconducted at temperatures between -2C and -0.3C at 0.1 MPa (octahedral shear stress). Unlikeprevious studies investigating temperatures close to the melting point, these experiments werecontinued through to high shear strains (>10%) to ensure that samples had developed the mechanicalanisotropy and corresponding enhanced flow rates that are associated with the microstructuralevolution that is typical of polar ice sheets. These data contribute to the continued development of a constitutive relation for polycrystalline icethat will improve the accuracy of ice sheet models, and are relevant to model studies utilizing inversemethods to infer the spatial extent of basal sliding.
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