Spring Snow to Summer Puddles: Change on the Arctic Sea Ice Surface
Melinda Webster - University of Washington
The oldest records of the Arctic sea ice pack illustrate a frozen, yet dynamic icescape composed of hummocks and weathered ridges draped in thick snow. In recent decades, the effects of climate change have morphed this image: the Arctic sea ice pack is younger, thinner, and more seasonal. As a result, the geophysical properties of its surface are changing and impacting its ice mass balance. This work investigates the changes on the Arctic sea ice surface, giving special emphasis to snow, melt ponds, and surface roughness. Recent in situ and airborne observations were used to extend the snow climatology to the contemporary period. Through this, we identified that the snow cover has thinned by 37 ± 29% in the western Arctic and 56 ± 33% in the Beaufort and Chukchi seas. The decrease was attributed to delayed sea ice freeze-up; in autumn, snow falls into the ocean and melts, rather than accumulating on sea ice. To explore the role of snow in sea ice melt processes, spring snow distribution and summer melt pond evolution were evaluated at a Lagrangian site on the edge of the perennial ice zone. A combination of in situ, airborne, and satellite data were used to study the relationships between snow, melt ponds, and surface roughness on different sea ice types from pre-melt conditions in April to advanced melt in September. Surprisingly, snow was thinnest on multiyear sea ice, with more than 47% of its snow cover being optically-thin. The thin snowpack likely contributed to the observed early melt pond formation; melt ponds formed ~3 weeks earlier on multiyear ice than first-year ice. The uniformity in melt pond behavior and distribution, as well as snow distribution, was inversely proportional to the level of surface roughness; uniformity increased with decreasing surface roughness. These results reveal that surface roughness, snow distribution, and melt pond evolution are intimately linked, and may provide insight on the future state of the Arctic sea ice cover.
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