Sea ice formation
Sea water with a salinity of about 34 per mille begins to freeze when its temperatures drops to around -1.89° C. Small millimeter sized crystals, called frazil ice, accumulate on the sea surface where they form slicks and give the sea surface a greasy appearance. This "grease ice" eventually aggregates into small ice chunks which turn into pancake-shaped ice floes when they rub against each other in rough seas. Eventually these the pancackes freeze together and form a solid ice cover. As time progresses and temperatures sink even further the ice continues to grow thicker. Strong winds and currents force pancakes or floes over each other, giving the ice a rough surface and a very rugged bottom. Reports by divers and photos taken by Under water vehicles have confirmed the extreme roughness of the underside, while the sea surface often appears flat due to the covering of snow.
The large expanse of sea ice which develops in this manner is not only a habitat on which animals may live, but also one in which organisms thrive. Ice formation processes therefore also play an important role in how these organisms get into the ice. The small frazil crystals referred to above are mixed down into the water during strong wave action. When they rise to the surface the crystals come into contact with the small micro-organisms, the so-called plankton. The organisms become entrapped between the crystals and thus end up in the grease ice and finally in the pancakes and solid pack ice. Another mechanism appears to be the simple pumping of water through the grease ice due to the wave motion. After the organisms have acclimatised to the colder conditions within the sea ice, and if sufficient light is available they will begin to grow and eventually they will colour the ice a greenish-brown.