Southern Ocean

Southern Ocean or Antarctic Ocean, southernmost parts of the Atlantic, Indian, and Pacific oceans, classified in 2000 as a fifth world ocean by the International Hydrographic Organization. Its northern boundary has been set at latitude 60° south, the Antarctic Convergence Zone, giving it a total area of 20.3 million sq km (7.8 million sq mi); it is the fourth-largest of the Earth's five oceans. Drake Passage, south of Cape Horn, is the narrowest part of the ocean. A large part of the Southern Ocean is covered by the ice shelf that surrounds Antarctica. Most of the continental shelf is under this ice. The rest of the ocean is deep, with four especially deep basins in it, separated by submarine ridges. The ocean is a breeding ground for billions upon billions of small crustaceans known as krill that form the main diet of baleen whales. For many years the Southern Ocean was a destination of whaling ships, until an international treaty halted commercial whaling in 1988.