From Ponds to Predictions: What Do We Need to Know About Small-Scale Sea Ice Processes in a Rapidly Changing Arctic?

Abstract:

Areal coverage and spatial distribution of sea-ice melt ponds are key factors in determining the response of the Arctic Ocean’s ice cover to changes in atmospheric forcing, its importance in enhancing high-latitude warming and its function in polar marine ecosystems. A review of remote-sensing and field observations, in conjunction with process studies in coastal Alaska, highlights the importance of sub-floe scale ice properties and processes in controlling ponding, thereby constraining seasonal evolution and decay of the ice cover. Field observations and model simulations have shown how pond areal extent and hence ice albedo depend on the combination of snow or ice ablation rates, ice permeability and surface topography. Seasonal and short-term variations of these three factors explain much of the observed spatial and temporal variability in the large-scale pond areal fraction. Recent work on Alaska shorefast ice suggests that the snow-cover depth distribution may predetermine ponding patterns months ahead of spring melt. Specifically, through the formation of wind crusts, snow depth variations are locked in place. After onset of melt, formation and deepening of ponds is enhanced in thin-snow areas, with pond spatial patterns replicating snow dune topography. Both deepening of ponds and preferential pond drainage through small-scale flaws and cracks then constrain the eventual break-up of the ice cover. Field observations and aerial photography indicate that with increasing wave action in an ice-diminished Arctic Ocean, ponds and drainage features precondition ice for break-up and fragmentation. Model simulations by Schröder et al. (doi:10.1038/nclimate2203) hint at other, as of yet poorly understood mechanisms that link pond coverage to the degree of seasonal ice retreat. Key measurements and potential datasets that can help improve understanding and prediction of a changing ice cover on seasonal scales will be discussed.