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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/tc-2018-213
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2018-213
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 07 Nov 2018

Research article | 07 Nov 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal The Cryosphere (TC).

Microstructure and texture evolution in polycrystalline ice during hot torsion. Impact of intragranular strain and recrystallization processes

Baptiste Journaux1,2, Thomas Chauve2,3, Maurine Montagnat2, Andrea Tommasi4, Fabrice Barou4, David Mainprice4, and Léa Gest2 Baptiste Journaux et al.
  • 1NASA Astrobiology Institute, Department of Earth and Space Sciences, University of Washington, Seattle, USA
  • 2Université Grenoble Alpes, CNRS, IRD, G-INP, IGE, 38000 Grenoble, France
  • 3PGP, Department of Geoscience, University of Oslo, Norway
  • 4Géosciences Montpellier, Université de Montpellier/CNRS, 34095 Montpellier, France

Abstract. Torsion experiments were performed in polycrystalline ice at high temperature (0.97Tm) to reproduce simple shear conditions close to those encountered in ice streams and at the base of fast flowing glaciers. As well documented more than 30 years ago (Hudleston, 1977; Bouchez and Duval, 1982), under simple shear ice develops a two-maxima c-axis texture, which evolves rapidly into a single cluster texture with c-axis perpendicular to the shear plane. This evolution still lacks a physical explanation. Current viscoplastic modeling approaches on ice involving dislocation slip on multiple slip systems (basal pyramidal, and prismatic) fail to reproduce it. Dynamic recrystallization mechanisms that occur in both laboratory conditions and in natural setups are likely candidates to explain the texture evolution observed. In this study, we use Electron BackScattering Diffraction (EBSD) and Automatic Ice Texture Analyzer (AITA) to characterize the mechanisms accommodating deformation, the stress and strain heterogeneities that form under torsion of an initially isotropic polycrystalline ice sample at high temperature, and the role of dynamic recrystallization in accommodating these heterogeneities. These analyses highlight an interlocking microstructure, which results from heterogeneity-driven serrated grain boundary migration, and sub-grain boundaries composed by dislocations with [c]-component Burgers vector, indicating that strong local stress heterogeneity develops, even at high temperature and high finite shear strain. Based on these observations, we propose that that nucleation by bulging, assisted by sub-grain boundary formation, is a very likely candidate to explain the progressive disappearance of the texture cluster at low angle to the shear plane and the stability of the one normal to it. We therefore strongly support the development of new models limiting dislocation slip on non-basal slip system and allowing for efficient polygonization by an association of bulging and formation of sub-grain boundaries with a significant [c]-component.

Baptiste Journaux et al.
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Latest update: 16 Nov 2018
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Short summary
Ice mechanics is an important tool to better predict the response of glaciers or polar ice sheets to climate variations. Nevertheless our current predictive abilities are limited as the microscale mechanisms responsible for ice creep are poorly identified. We show in this study, using state of the art experimental techniques, which recrystallization processes are controling ice deformation. This will allow realistic simulations, necessary to predict the long term effects on ice land masses.
Ice mechanics is an important tool to better predict the response of glaciers or polar ice...
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