Sea ice is formed from ocean water that freezes. Because the oceans consist of saltwater, this occurs at about minus 1.8 degrees Celsius (28.8 degrees Fahrenheit). Most Antarctic sea ice occurs annually, meaning it forms in the winter and melts during the summer. Sea ice regulates exchanges of heat, moisture and salinity in the polar oceans. It insulates the relatively warm ocean water from the cold polar atmosphere except where cracks, or leads, in the ice allow exchange of heat and water vapor from ocean to atmosphere in winter. The number of leads determines where and how much heat and water are lost to the atmosphere, which may affect local cloud cover and precipitation.
- Antarctic sea ice extent in the winter: 18 million square kilometers
- Antarctic sea ice extent in the summer: 3 million square kilometers
- Some types of sea ice: fast, pack, drift
- Multi-year ice: ice that has survived at least one melt season; it is typically 2 to 4 meters thick