Meghana Ranganathan , Brent Minchew, Colin R. Meyer, Matej Pec

The initiation of fractures and fast flow in floating regions of Antarctica have the potential to destabilize large regions of the grounded ice sheet, leading to significant sea-level rise. While observations have shown rapid, localized deformation and damage in the margins of fast-flowing glaciers, there remain gaps in our understanding of how rapid deformation affects the viscosity and toughness of ice. Here we derive a model for dynamic recrystallization of ice that includes a novel representation of migration recrystallization. This mechanism is absent from existing models and is likely dominant in warm areas undergoing rapid deformation, such as shear margins in ice sheets. While solid earth studies find fine-grained rock in shear zones, here we find elevated ice grain sizes (>10 mm) due to warmer temperatures and high strain rates activating migration recrystallization. Large grain sizes implies that ice in shear margins deforms primarily by dislocation creep, suggesting a flow-law stress exponent of n=4 rather than the canonical n=3. Further, we find that this increase in grain size results in a decrease in tensile strength of ice by ~75% in the margins of glaciers. Thus, this increase in grain size softens the margins of fast-flowing glaciers and makes ice shelf margins more vulnerable to fracture than previously supposed. These results also suggest the need to consider the effects of dynamic recrystallization in large-scale ice-sheet modeling.