National Geographic Recognizes New 5th Ocean

On World Oceans Day, Nat Geo cartographers say the swift current circling Antarctica keeps the waters there distinct and worthy of their own name: the Southern Ocean. National Geographic reports: Since National Geographic began making maps in 1915, it has recognized four oceans: the Atlantic, Pacific, Indian, and Arctic Oceans. Starting on June 8, World Oceans Day, it will recognize the Southern Ocean as the world's fifth ocean. 'The Southern Ocean has long been recognized by scientists, but because there was never agreement internationally, we never officially recognized it,' says National Geographic Society Geographer Alex Tait. Geographers debated whether the waters around Antarctica had enough unique characteristics to deserve their own name, or whether they were simply cold, southern extensions of the Pacific, Atlantic, and Indian Oceans.

While the other oceans are defined by the continents that fence them in, the Southern Ocean is defined by a current. Scientists estimate that the Antarctic Circumpolar Current (ACC) was established roughly 34 million years ago, when Antarctica separated from South America. That allowed for the unimpeded flow of water around the bottom of the Earth. The ACC flows from west to east around Antarctica, in a broad fluctuating band roughly centered around a latitude of 60 degrees south -- the line that is now defined as the northern boundary of the Southern Ocean. Inside the ACC, the waters are colder and slightly less salty than ocean waters to the north.

Extending from the surface to the ocean floor, the ACC transports more water than any other ocean current. It pulls in waters from the Atlantic, Pacific, and Indian Oceans, helping drive a global circulation system known as the conveyor belt, which transports heat around the planet. Cold, dense water that sinks to the ocean floor off Antarctica also helps store carbon in the deep ocean. In both those ways, the Southern Ocean has a crucial impact on Earth's climate. For now, by fencing in the frigid southern waters, the ACC helps keep Antarctica cold and the Southern Ocean ecologically distinct. Thousands of species live there and nowhere else. By drawing attention to the Southern Ocean, the National Geographic Society hopes to promote its conservation.

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