Dynamics of ice mass deformation: Linking processes to rheology, texture, and microstructure

Prediction of glacier and polar ice sheet dynamics is a major challenge, especially in view of changing climate. The flow behavior of an ice mass is fundamentally linked to processes at the grain and subgrain scale. However, our understanding of ice rheology and microstructure evolution based on conventional deformation experiments, where samples are analyzed before and after deformation, remains incomplete. To close this gap, we combine deformation experiments with in situ neutron diffraction textural and grain analysis that allows continuous monitoring of the evolution of rheology, texture, and microstructure. We prepared ice samples from deuterium water, as hydrogen in water ice has a high incoherent neutron scattering rendering it unsuitable for neutron diffraction analysis. We report experimental results from deformation of initially randomly oriented polycrystalline ice at three different constant strain rates. Results show a dynamic system where steady-state rheology is not necessarily coupled to microstructural and textural stability. Textures change from a weak single central c axis maxima to a strong girdle distribution at 35° to the compression axis attributed to dominance of basal slip followed by basal combined with pyramidal slip. Dislocation-related hardening accompanies this switch and is followed by weakening due to new grain nucleation and grain boundary migration. With decreasing strain rate, grain boundary migration becomes increasingly dominant and texture more pronounced. Our observations highlight the link between the dynamics of processes competition and rheological and textural behavior. This link needs to be taken into account to improve ice mass deformation modeling critical for climate change predictions. Key Points Technique combination allows monitoring of texture, rheology and structure Ice deforms as a highly dynamic system Deformation process competition governs ice deformation behaviour