The five oceans

The Pacific Ocean covers about 168.7 million square kilometres, more than all the land on Earth put together.

One ocean with five names

NOAA puts it plainly: there is only one global ocean. The salt water that covers about 71 percent of the Earth is connected all the way round, and a drop of water off the coast of Korea can, in time, reach the coast of Brazil. Still, the continents split that water into basins, and people have named them for practical, historical and scientific reasons. For a long time there were four named oceans: the Pacific, Atlantic, Indian and Arctic. Most countries, including the United States, now recognise a fifth, the Southern Ocean around Antarctica.

The Southern Ocean is the newest name. The U.S. Board on Geographic Names defines it as the water from the coast of Antarctica north to 60 degrees south latitude. Its limits were proposed to the International Hydrographic Organization in 2000, but not every member agreed, and the proposal has not been ratified. National Geographic began marking it on its maps on World Oceans Day, 8 June 2021. What makes it a separate body of water is a current: the Antarctic Circumpolar Current flows from west to east all the way round the continent, and scientists estimate it formed roughly 34 million years ago, when Antarctica separated from South America.

Sizes and depths

By area the order is Pacific, Atlantic, Indian, Southern and Arctic. The Factbook gives the Pacific as about 168.7 million square kilometres, almost twice the Atlantic at 85.1 million. The Indian Ocean is 70.6 million, the Southern 22.0 million and the Arctic, the smallest, 15.6 million. Together that is about 361.9 million square kilometres, and the Pacific alone is 46.6 percent of it. The Pacific is also the deepest on average, about 4,080 metres, while the Arctic averages only about 1,205 metres because much of it lies over wide continental shelves.

Where the names come from

The Pacific was named by Ferdinand Magellan, who crossed it in 1520 and 1521 while sailing round the world and called it Mar Pacifico, the peaceful sea, after the calm water he met. The Atlantic takes its name from an ancient Greek phrase for the waters beyond the Strait of Gibraltar, the sea of Atlas. The Indian Ocean is named after India, which makes up much of its northern shore. Arctic comes from the Greek arktikos, meaning near the bear or northern, a reference to the Great Bear in the northern sky or, by another reading, to the Little Bear, which holds the North Star.

Almost all of Earth’s water is in these oceans. The Factbook puts saltwater at about 97.5 percent of all water. Of the 2.5 percent that is fresh, about two thirds is frozen, mostly in mountain glaciers and the Antarctic ice sheets. If all the surface ice on Earth melted, sea level would rise by about 70 metres, enough to drown most of the world’s coastal cities.