Modelling of deformtion and recrystallisation microstructures in polar ice

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Knowledge of the deformation mechanisms of polar ice is of crucial importance to predict the flow of polar ice caps and hence their influence on the global climate. Deformation of ice also impacts on one of the best climate record on Earth: the individual ice layers observed in deep ice cores. Microstructures form the main record of in situ deformation, by revealing the deformation processes that operate during the flow of an ice sheet. New microstructural analysis techniques developed at AWI now allow a much more detailed and extensive assessment of these microstructures than ever before. Within this project, a start has been made with the numerical modelling of ice microstructures, using the comprehensive modelling platform Elle . After updating and refining algorithms, Elle is now capable of simulating several of the main processes that occur in polar ice: recrystallisation, grain growth and crystal-plastic deformation. In the course of the project s remaining 26 months1 existing routines for two-phase materials will be adapted to model ice with bubbles or clathrates, and to model intracrystalline recovery. Results of systematic simulations will be compared quantitatively with theoretical analyses and the unique microstructure dataset available at AWI of several firn and ice cores (especially the EPICA–DML deep ice core). In particular we will critically reassess the role of grain boundary formation and migration that continually reworks the microstructure. The results of this project will improve our knowledge of the mechanical behaviour of polar ice and refine the analysis of climatic records, which are essential to ice sheet and climate modelling.