Softening of Temperate Ice by Interstitial Water

Ice at depth in ice-stream shear margins is thought to commonly be temperate, with interstitial meltwater that softens ice. Models include this softening extrapolate results of a single experimental study which ice effective viscosity decreased by factor ?3 over water contents ?0.01–0.8%. Modeling indicates localizes strain and through heating increases the bed, enhancing basal slip. To extend data higher contents, we lab-made confined compression large ring-shear device. rings initial mean grain sizes 2–4 mm are kept pressure-melting temperature sheared controlled rates peak stresses ?0.06–0.20 MPa, spanning most estimated shear-stress range West Antarctic margins. Final 8–13 mm. Water content measured inducing freezing front ice-ring edges, tracking its movement inward thermistors, fitting solutions relevant Stefan problem. Results indicate two creep regimes, below above ?0.6%. Comparison values secondary those tertiary from earlier for 0.2–0.6%, about twice as sensitive than creep. Above 0.6%, within 25% creep, suggesting stress-limiting mechanism greater 0.6% insensitive fabric development At ?0.6–1.7%, independent content, nearly linear-viscous. Minimization intercrystalline stress heterogeneity grain-scale melting refreezing approach an upper bound grain-boundary films thicken might account regimes.