Adam Treverrow1, Bridie Le’Gallais2
1Antarctic Climate And Ecosystems Cooperative Research Centre, Hobart, Australia, 2University of Tasmania, Hobart, Australia
The dynamic behaviour of the Antarctic ice sheet is controlled by both creep deformation and the occurrence of sliding at the base of the ice sheet. The activity of these processes is highly temperature dependent 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 typically a power-law relationship between the stresses driving the flow and the corresponding strain rates, with a separate term describing the temperature dependence. Many models use a simplified prescription of the temperature dependence which does not adequately describe the sensitivity of deformation rates to temperature within ~5°C of the melting point. This leads to an underestimation of strain rates in the warmest ice.
While the increased sensitivity of deformation rates to temperature near the melting point is clearly demonstrated by laboratory experiments, it is constrained by a relatively small number of observations due to the inherent difficulties in conducting experiments at high temperatures. Here we present preliminary results from an experimental program designed to improve the constraint on deformation rates at temperatures close to the melting point. Simple shear deformation experiments were conducted at temperatures between -2°C and -0.3°C at 0.1 MPa (octahedral shear stress). Unlike previous studies investigating temperatures close to the melting point, these experiments were continued through to high shear strains (>10%) to ensure that samples had developed the mechanical anisotropy and corresponding enhanced flow rates that are associated with the microstructural evolution that is typical of polar ice sheets.
These data contribute to the continued development of a constitutive relation for polycrystalline ice that will improve the accuracy of ice sheet models, and are relevant to model studies utilizing inverse methods to infer the spatial extent of basal sliding.