| Summary: | Scientific Committee on Antarctic Research (SCAR) Online Conference, August 5, 2020 Researchers are recognising rapid changes occurring at the ice-ocean interface: changes that potentially increase the driving force for sea-ward motion of ice sheets. Estimation of the time-scale of the ice sheet response and resultant sea-level rise depends critically on realistic ice flow laws. Ice deformation is a significant component of ice flow: data from laboratory experiments can be extrapolated to natural strain-rates. The strain rate at a given stress results from the addition of the rates related to grain-size sensitive and grain-size insensitive mechanisms. All ice experiments, where grain-size has been varied, show grain-size dependency at low strain (< 3%). As strain increases to intermediate (~20%) values, viscosity reduces corresponding to changes in fabric and grain-size. At strains higher than 20% to 50% an approximately steady-state viscosity is achieved, corresponding to microstructural steady-state. At low strains, the strain rate dependency on stress (stress exponent: n) depends on ice grain-size and conditions (particularly stress) and varies between ~ 2 and ~ 4. Intermediate n values (3 to 3.5) are common and have little relevance to ice deformation at high strain. Grain-size at steady-state is inversely proportional to the flow stress, through a piezometer relationship. At steady-state, grain-size sensitive mechanisms contribute significantly to deformation, but because the stress controls the grain-size, which in turn controls the viscosity these effects are hidden. Experimental steady-state flow laws have n values of ~ 4 or higher: these are applicable to ice at high strain and match recent estimates from natural systems.
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