The highly nonlinear viscosity of fast-flowing glacier ice

Meghana Ranganathan , Brent Minchew

Glacier flow modulates sea level and is governed by the viscous deformation of ice. Multiple molecular-scale mechanisms facilitate viscous deformation, but it remains unclear how each contributes to glacier-scale deformation and how to represent them in ice-flow models. Here, we present a model of ice deformation that unifies existing estimates of the viscous parameters and provides a framework for estimating their values. We infer from observations the dominant deformation mechanisms in the Antarctic Ice Sheet, showing that, contrary to long-standing assumptions, dislocation creep, with viscous stress exponent n=4, likely dominates in all fast-flowing areas. This increase from the canonical n=3 changes the stability portrait of marine ice sheets by reducing the likelihood of unstable steady-state configurations on reverse bed slopes under given climate conditions.