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Melt ponds on summer Arctic sea ice control surface albedo, governing energy and mass balance of the ice. The date ponds first form has been connected to interannual variations in ice retreat. Here we evaluate the surface energy balance that governs this critical pond formation date. A three-dimensional sea ice model with resolved melt ponds is used to diagnose pond onset date at a coastal site across years with observed surface fluxes but incomplete pond observations. Results show that the combined sensible and latent heat flux is the best predictor of pond formation date. This finding supports the hypothesis that synoptic weather events transporting warm, moist air into the Arctic are key to initiating pond formation, triggering albedo feedbacks, and, by extension, ice retreat. Changes in timing and frequency of spring warm air incursions may have significant implications on the ice cover and provide predictive power over seasonal ice retreat.

Plain Language Summary The Arctic is warming faster than many areas around the globe. One reason for this is because earlier melt of sea ice results in heating from greater sunlight absorption. Melt ponds, pools of meltwater on the ice surface, are important in darkening the ice. We seek to understand what causes ponds to start forming and find that warm, moist air blowing in from the south may play a large role. Our study examines data from the past 18 years and uses a model of sea ice to estimate the energy source that melts snow and leads to ponds forming. Our model shows that sunlight is the source of most of the energy but that pond formation is prevented by cooling from cold air passing over the surface and from infrared radiation loss to space. We find that when warming exceeds the loss of surface heat, ponds form. We determined that reduction in and/or reversal of cooling by the air is more important in controlling melting at our coastal study site than infrared radiation loss to space.