Southern Ocean Southern Ocean The Southern Ocean, also known as the Antarctic Ocean or the Austral Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. As such, it is regarded as the fourth-largest of the five principal oceanic divisions: smaller than the Pacific, Atlantic, and Indian Oceans but larger than the Arctic Ocean. This ocean zone is where cold, northward flowing waters from the Antarctic mix with warmer subantarctic waters. By way of his voyages in the 1770s, Captain James Cook proved that waters encompassed the southern latitudes of the
Indian Ocean point of Tasmania. The northernmost extent of the Indian Ocean is approximately 30° north in the Persian Gulf. The Indian Ocean covers , including the Red Sea and the Persian Gulf but excluding the Southern Ocean, or 19.5% of the world's oceans; its volume is or 19.8% of the world's oceans' volume; it has an average depth of and a maximum depth of . The ocean's continental shelves are narrow, averaging in width. An exception is found off Australia's western coast, where the shelf width exceeds . The average depth of the ocean is . Its deepest point is Sunda