Reconciling Summer Ice Hydraulics with Simulations of Arctic Sea-Ice Retreat

Seasonal melt and retreat of the Arctic sea-ice cover is strongly influenced by the pooling of meltwater at the ice surface. Melt ponds control summer ice albedo, typically reducing it by 30 to 50 % relative to that of bare ice. The formation and seasonal waxing and waning of ponds is driven by the retention of melt water at the surface of a floating slab of ice. Thus, ponding is constrained by the permeability of the underlying ice, surface meltwater production rates and the topography of the ice. The interplay of these variables and the important role of snow in modulating all three are such that under present-day conditions, Arctic sea ice can exhibit pond coverages ranging from close to zero to well over one half of the total surface area. Recent changes in the age structure of the Arctic ice pack likely brought about significant changes in pond coverage and hence ice albedo. Prediction of pond coverage is challenging, not least because of the great sensitivity to even minor variations in surface topography and the dependence on snow depth distribution. The presentation will examine the implications of these findings for climate-model simulations of the Arctic ice pack and discuss the need to account for ponding processes in order to predict and track future changes in the sea ice heat and mass budget.