Sunlight, Sea Ice, Ponds, and Oceans; What Is Driving the Ice-Albedo Feedback?

There has been a general decline in the extent and thickness of the Arctic sea ice cover in the past few decades, and a shift from a multiyear ice cover to one that is predominantly seasonal. The ice-albedo feedback is one of several factors contributing to this decline. It has the potential to accelerate ongoing changes. A synthesis of field observations, satellite results, and radiative transfer modeling indicates that decreases in ice concentration have increased the solar energy deposited in the upper ocean over the past few decades. The largest increases in total annual solar heat input, as much as 4% per year, occurred in the Chukchi Sea region. Results show two key drivers of albedo: the areal fraction of melt ponds and the timing of melt onset. There are major differences in pond evolution between seasonal and multiyear ice. Melt ponds on undeformed seasonal ice reach areal fractions as large as 80% in only a few days. Just as quickly, coverages can drop to 10% as the ponds drain. In multiyear ice, the pond fraction increases rapidly early in the melt season, declines sharply after about a week, and then increased gradually until fall freezeup. Determining the evolution of melt ponds remains a major challenge in ice – albedo studies. Changes in the timing of the summer melt season have resulted in alterations in the evolution of albedo of the Arctic sea ice cover, and consequently in the partitioning of solar energy. The evolution of albedo, and hence the total solar heating of the ocean, is sensitive to the date of melt onset. Autonomous measurements of the ice mass balance are being used to investigate the impact of changes in solar heating. Ice surface melt has shown only a modest correlation to net solar heat input to the ice. However, there is a strong correlation between solar heat input to the ocean and bottom melting.