Snowpack thermal regime controls ice layer permeability

Abstract Increased occurrence of high melt summers across Arctic ice caps and the Greenland Ice Sheet creates thicker, more numerous ice layers within the near surface snow and firn of their accumulation zones. Ice layers may reduce vertical percolation of surface meltwater, promote lateral runoff, reduce refreezing at depth in underlying snow and firn promoting a positive feedback towards more negative surface mass balance. Despite their significance for ice sheet mass balance, controls on ice layer permeability are poorly understood. Here, we explore ice layer permeability using cold-laboratory snowpack experiments with predefined thermal regimes and ice layer thicknesses. We found that in a cold thermal regime (−3°C), ice layers (5–20 mm thick) within the snowpack are impermeable. Meltwater runs off laterally or ponds and subsequently refreezes within 3 h. With temperate conditions (0°C), meltwater ponds over ice layers (10–60 mm thick) without freezing. Temperate ice layers are permeable over timescales of ∼4 to 18 h. We propose that permeability of refrozen ice layers is primarily a function of thermal regime and that ice layer thickness is a secondary control. Our findings pave the way for improved snow and firn model parameterizations of ice layer permeability and ice sheet mass loss projections.