Indian Ocean

The African, Indian, and Antarctic crustal plates converge in the Indian Ocean. Their junctures are marked by branches of the Mid-Oceanic Ridge forming an inverted Y, with the stem running south from the edge of the continental shelf near Mumbai, India. The eastern, western, and southern basins thus formed are subdivided into smaller basins by ridges. The ocean's continental shelves are narrow, averaging 200 kilometers (125 mi) in width. An exception is found off Australia's western coast, where the shelf width exceeds 1,000 kilometres (600 mi). The average depth of the ocean is 3,890 metres (12,760 ft). Its deepest point, is in the Java Trench. North of 50° south latitude, 86% of the main basin is covered by pelagic sediments, of which more than half is globigerina ooze. The remaining 14% is layered with terrigenous sediments. Glacial outwash dominates the extreme southern latitudes.

A spring 2000 decision by the International Hydrographic Organisation delimited a fifth world ocean, stripping the southern portions of the Indian Ocean. The new ocean extends from the coast of Antarctica north to 60° south latitude which coincides with the Antarctic Treaty Limit. The Indian Ocean remains the third-largest of the world's five oceans.

Major choke points include Bab el Mandeb, Strait of Hormuz, Strait of Malacca, southern access to the Suez Canal, and the Lombok Strait. Seas include Andaman Sea, Arabian Sea, Bay of Bengal, Great Australian Bight, Gulf of Aden, Gulf of Oman, Laccadive Sea, Mozambique Channel, Persian Gulf, Red Sea, Strait of Malacca, and other tributary water bodies.