Sea ice is frozen ocean water. It occurs in both the Arctic and Antarctic and can cover large extents of water. It grows during the winter months and melts during the summer months, but some sea ice remains all year in certain regions. About 15 percent of the world's oceans are covered by sea ice during part of the year. The freezing temperature of salt water is lower than fresh water; ocean temperatures must reach -1.8° C Celsius (28.8°F) to freeze.
