Abstract

Creep due to ice flow is generally thought to be the main cause for the formation of crystallographic preferred orientations (CPOs) in polycrystalline anisotropic ice. However, linking the development of CPOs to the ice flow history requires a proper understanding of the ice aggregate's microstructural response to flow transitions. In this contribution the influence of ice deformation history on the CPO development is investigated by means of full-field numerical simulations at the microscale. We simulate the CPO evolution of polycrystalline ice under combinations of two consecutive deformation events up to high strain, using the code VPFFT/ELLE. A volume of ice is first deformed under co-axial boundary conditions, which results in a CPO. The sample is then subjected to different boundary conditions (co-axial or non-coaxial) in order to observe how the deformation regime switch impacts on the CPO. The model results indicate that the second flow event tends to destroy the first, inherited fabric, with a range of transitional fabrics. However, the transition is slow when crystallographic axes are critically oriented with respect to the second imposed regime. Therefore, interpretations of past deformation events from observed CPOs must be carried out with caution, particularly, in areas with complex deformation histories.

Highlights

  • Deformation of a grain aggregate by dislocation creep leads to a crystallographic preferred orientation (CPO), called fabric

  • Because ice can be affected by differences in temperature and stress configurations during ice-sheet flow, unravelling the ice deformation history from c-axis fabrics observed in natural ice samples can be challenging

  • This study presents a series of full-field numerical simulations of 475 polycrystalline ice deformed under two consecutive flow regimes

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Summary

Introduction

During the last two decades sea level rise has accelerated in association with global climate 45 change (Nerem et al, 2018), but the limited knowledge available on how fast ice flows in ice sheets along with uncertain boundary conditions (Edwards et al, 2021), give a wide range in long-term sea level rise predictions. As in the case of laboratory experiments, most numerical studies to date have focused on systems starting with an initially random CPO to which a single deformation event is applied. Very useful, these experimental and numerical studies can only represent a limited range of real natural scenarios, where ice aggregates with no strain history are subjected to stress. Considering that polar ice typically experiences multiple changes in deformation regime 100 during ice-sheet flow, systematic studies of CPO development during multi-stage deformation histories are essential This contribution intends to fill this knowledge gap by providing a study of the multi-stage deformation of ice samples and the resulting CPOs for different settings. We analyse the CPO developed during these deformation events in order to determine the kinematic conditions for the preservation, modification or destruction of CPO's in ice

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