Sea Ice in Antarctica
Beyond the ice shelves is the sea. When the sea freezes it forms a salty type of ice, sea ice. The area covered by sea ice varies with the seasons, around 3 million km² in February, around 20 million km² in October.
Although only a few metres thick sea ice insulates the sea and limits the amount of sunlight reaching it. Lack of light limits growth of phytoplankton in the sea, though algae do multiply in the sea ice itself, sometimes turning it brown. The insulation effect reduces heat transfer between ocean and atmosphere, keeping the air cold and dry. Finally, as sea ice melts it cools both ocean and atmosphere. Because it limits energy transfer, the extent of sea ice is critical to the climate of the Southern Ocean.