| Summary: | During the spring-to-summer transition, the snow cover on Arctic sea ice melts and meltwater pools on the surface to form distinct ponds. In Dease Strait (Nunavut), June 2014, the transition from a cold pre-melt state to >95% flooded sea ice surface was particularly dramatic as the level landfast first year sea ice facilitated extensive lateral spreading of meltwater. In this study, the surface energy budget is presented for the ice cover during this transformation. The key to the extensive flooding was that an initial snow-melt transition was interrupted by a low-pressure system during which ~10 cm new snow was deposited. A subsequent return to sub-zero temperatures triggered refreezing of meltwater, causing widespread formation of superimposed and interposed ice that decreased the near-surface permeability of the ice cover. Our results highlight how the timing of transient weather events greatly influence seasonal transitions, which can display large interannual variability. After a three-week delay, snow-melt initiated again and proceeded rapidly leading to near-complete flooding of the sea ice surface for four days. The albedo of the flooded ice was high (~0.35), reflecting the presence of the bubble-laden superimposed ice layer, but once it eroded the melt pond albedo decreased to a more typical level (~0.20). Our observations indirectly suggest that the formation of impermeable ice layers – superimposed and interposed ice – blocked the drainage of meltwater to the ocean and was key to understand seasonal transitions – flooding and meltwater drainage – during the melt season. Future challenges remain to quantitatively measure the presence of these layers and their effect on sea ice porosity and permeability while sea ice temperatures are near the melting point. February 2018
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