Surrounding Antarctica are the southern parts of the Pacific, the Atlantic, and the Indian Oceans. The Antarctic Convergence, which encircles Antarctica roughly 1,500 kilometers off the coast, divides the cold southern water masses and warmer northern waters. An ocean current, the world's largest, moves eastward around the continent at an average speed of about half a knot. Sea ice up to 3 meters thick forms outward from the continent every winter, making a belt 500 to 1,500 kilometers wide. Even in summer the sea ice belt is 150 to 800 kilometers in most places. The area of sea ice varies from 3 million square kilometers in summer to 20 million square kilometers in late winter.