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. Torsion experiments were performed in polycrystalline ice at high temperature( 0.97 Tm ) to reproduce the simple shear kinematics that are believed todominate in ice streams and at the base of fast-flowing glaciers. As clearlydocumented more than 30 years ago, under simple shear ice develops atwo-maxima c  axis crystallographic preferred orientation (CPO), whichevolves rapidly into a single cluster CPO with a c  axis perpendicular to theshear plane. Dynamic recrystallization mechanisms that occur in bothlaboratory conditions and naturally deformed ice are likely candidates toexplain the observed CPO evolution. In this study, we use electronbackscatter diffraction (EBSD) and automatic ice texture analyzer (AITA) tocharacterize the mechanisms accommodating deformation, the stress and strainheterogeneities that form under torsion of an initially isotropicpolycrystalline ice sample at high temperature, and the role of dynamicrecrystallization in accommodating these heterogeneities. These analyseshighlight an interlocking microstructure, which results fromheterogeneity-driven serrated grain boundary migration, and sub-grainboundaries composed of dislocations with a [c] -component Burgers vector,indicating that strong local stress heterogeneity develops, in particular,close to grain boundaries, even at high temperature and high finite shearstrain. Based on these observations, we propose that nucleation by bulging,assisted by sub-grain boundary formation and followed by grain growth, is avery likely candidate to explain the progressive disappearance of the c  axis CPO cluster at low angle to the shear plane and the stability of theone normal to it. We therefore strongly support the development of newpolycrystal plasticity models limiting dislocation slip on non-basal slipsystems and allowing for efficient accommodation of strain incompatibilitiesby an association of bulging and formation of sub-grain boundaries with asignificant [c]  component.

the cryosphere

Recrystallization processes, microstructure and crystallographic preferred orientation evolution in polycrystalline ice during high-temperature simple shear