ABSTRACT
This chapter describes various aspects of sea ice formation and melt before the Arctic and Antarctic Sea ice systems and summarises the changes to the sea ice that are occurring there. Sea ice forms when the ocean surface reaches its salinity-dependent freezing point. In summer, the snow and sea ice melt, and ridges become smaller and more rounded. Thinner ice types normally entirely melt during the summer, and sea ice persists only in higher latitudes, leaving behind an increasing region of Open Ocean. In the Arctic the melting snow cover forms melt ponds, and these play a critical role in enhancing the melt of sea ice by changing its albedo. Antarctica possesses a largely seasonal ice cover which has a greater winter extent than Arctic sea ice, and because the winter ice extent exceeds that of the Arctic, the maximum global sea ice extent coincides with the Antarctic winter.
