The evolution of ice fabrics: A continuum modelling approach validated against laboratory experiments

Abstract

There remains a significant challenge to model ice crystal fabrics both accurately and efficiently within ice-sheet models. We develop the first fully constrained continuum model, validated against experiments, able to predict the evolution of a crystal fabric for any flow field or temperature. For this, we apply a mesoscopic continuum model describing the evolution of a mass distribution function of c-axis orientations. The model assumes that ice deforms by dislocation creep with slip primarily along the basal plane, and incorporates the effects of rigid-body rotation, migration recrystallization and rotational recrystallization. We solve the model using a new spectral method, which is computationally highly efficient. By constraining the model parameters using data from laboratory experiments in simple shear, we provide the first estimates of the fundamental dimensionless parameters controlling the importance of different deformation and recrystallization processes as functions of temperature, as well as the first constraints on the strain rate dependence of these parameters. With no further fitting, we apply the model to the case of compression, yielding excellent quantitative agreement with observed fabrics from corresponding experiments. The combination of the model, the spectral method and the parameter constraints as functions of temperature provide accurate and efficient predictions of ice crystal fabric evolution for general deformations, temperatures and strain rates. The model-solver (SpecCAF) can, in principle, be extended to other important polycrystalline materials including olivine, the key material in mantle dynamics.