The Declining Arctic Sea Ice Cover: In Situ Insights and Synthetic Finding

The observational record indicates that the arctic sea ice cover is undergoing dramatic changes in its extent and thickness. As part of the Arctic Observing Network, autonomous drifting ice mass balance (IMB) buoys are being used to observe ice growth and melt and to provide important in situ insights to better understand the nature of the sea ice decline. Results from these buoys and manned ice camps show considerable regional and interannual variability in both surface and bottom melting. Summer melting in the high Arctic north of Greenland and at the North Pole Environmental Observatory has typically been modest in the past decade, with annual values less than 0.5 m. In comparison, there has been a significant increase in melting in the Beaufort Sea region in recent years, particularly at the bottom of the ice. A synthesis of model estimates of incident solar irradiance, satellite-derived ice concentrations, and observed albedos was used to investigate the role of solar radiation in the observed changes in ice mass balance. Results indicate a general trend of increasing solar heat input to the arctic ice-ocean system due to albedo changes induced by reductions in ice concentration and longer melt seasons. There is only a modest correlation between the net solar heat input to the ice and the observed amount of surface melt. In contrast there is a strong correlation between solar heat input to the ocean and bottom melting. These results suggest that local solar heating is the predominant source of energy for bottom melting and that additional factors, such as longwave radiation, impact surface melting. The Beaufort Sea region showed large increases in total annual solar heat input, averaging 4% per year. Ice melt in the Beaufort Sea displays an ice-albedo feedback signature, with more open water causing more solar heat to be absorbed, resulting in more melting and more open water.