A microstructural rheological model for transient creep in polycrystalline ice

TL;DR

This paper introduces a physics-based rheological model for polycrystalline ice that captures transient creep behavior, including a universal strain rate minimum, improving understanding of ice deformation relevant to sea-level rise.

Contribution

The model combines Kelvin-Voigt elements and a viscous component to accurately represent all three regimes of transient creep in polycrystalline ice, extending previous rheological descriptions.

Findings

The model reproduces the experimentally observed strain rate minimum at ~1% strain.

It captures all three regimes of transient creep in polycrystalline ice.

The framework can be integrated into ice-sheet models for better predictions.

Abstract

The slow creep of glacial ice plays a key role in sea-level rise, yet its transient deformation remains poorly understood. Glen's flow law, where strain rate is simply a function of stress, cannot predict the time-dependent creep behavior observed in experiments. Here we present a physics-based rheological model that captures all three regimes of transient creep in polycrystalline ice. The key components of the model are a series of Kelvin-Voigt mechanical elements that produce a power-law (Andrade) creep, and a single viscous element with microstructure and stress dependence that represents reorientation in the polycrystalline grains. The interplay between these components produces a minimum in the strain rate at approximately 1% strain, which is a universal but unexplained feature reported in experiments. Due to its transient nature, the model exhibits fractional power-law exponents in the stress dependence of the strain rate minimum, which has been conventionally interpreted as independent physical processes. Taken together, we provide a compact, mechanistic framework for transient ice rheology that generalizes to other polycrystalline materials and can be integrated into constitutive laws for ice-sheet models.