Sea Ice Formation

Sea ice formation begins when the surface layer of the ocean cools below its freezing point, roughly minus 1.8 degrees Celsius for typical seawater, and tiny ice crystals called frazil ice begin to form, which then coalesce into a soupy grease ice layer, consolidate into thin elastic sheets called nilas, and eventually thicken into solid pack ice as further heat is lost to the atmosphere. As the ice forms it rejects most of the salt it started with back into the water below, a process called brine rejection that increases the density and salinity of the underlying seawater and helps drive polar ocean circulation.