Dynamic recrystallization during deformation of polycrystalline ice: Insights from numerical simulations

The flow of glaciers and polar ice sheets is controlled by the highly anisotropic rheology of ice lh that is close to its melting point. To improve our knowledge of ice sheet dynamics, it is necessary to understand how dynamic recrystallisation controls ice microstructures and rheology at different boundary conditions that range from pure shear flattening at the top to simple shear near the base of the sheets. We present a series of two-dimensional numerical simulations that couple ice deformation with dynamic recrystallisation of various intensities, paying special attention to the effect of boundary conditions. The simulations show how similar orientations of c-axis maxima with respect to the finite deformation direction develop regardless the amount of dynamic recrystallisation and applied boundary conditions. In pure shear this direction is parallel to the maximum compressional stress, while it rotates towards the shear direction in simple shear. This leads to strain hardening and increased activity of non-basal slip systems in pure shear and to strain softening in simple shear. Therefore, it is expected that ice is effectively weaker in the lower parts of the ice sheets than in the upper parts. Strain-rate localisation occurs in all simulations, especially in simple shear cases. Recrystallisation suppresses localisation, which necessitates the activation of hard, non-basal slip systems.