The totality of ice found on and in the ocean.
The totality of ice found on and in the ocean. It is generally formed when seawater freezes; however, some may stem from river ice or inland ice. Because sea ice has a lower density than seawater, it floats atop the ocean. When it forms on the ocean, it sheds the majority of its salt into the seawater, which accounts for its low density. Since sea ice is predominantly formed from existing seawater, the sea level does not rise when it melts. The area and thickness of sea ice are subject to seasonal and multiyear variability. Sea ice is one of the most changeable parts of the cryosphere.