The Southern Ocean is the no. 4th contiguous open water surface on earth. It has a huge, 7,848,300 square mile (20,327,000 square km) area and 13,100-16,400 square feet (4,000-5,000 square meters) average depth. The Southern Ocean’s greatest known depth is 23,736 feet (7,235 meters), which can be found at South Sandwich Trench. Note: A decision by the International Hydrographic Organization in spring 2000 delimited a fifth world ocean.
A large body of recent oceanographic research has shown that the Antarctic Circumpolar Current (ACC), an ocean current that flows from west to east around Antarctica, plays a crucial role in global ocean circulation. The region where the cold waters of the ACC meet and mingle with the north’s warmer waters defines a distinct border – the Antarctic Convergence – which fluctuates with the seasons but encompasses a discrete body of water and a unique ecologic region.
The Convergence concentrates nutrients, which promotes marine plant life, and which, in turn, allows for a greater abundance of animal life.
In 2000, the International Hydrographic Organization delimited the Convergence waters as a fifth world ocean – the Southern Ocean – by combining the southern portions of the Atlantic Ocean, Indian Ocean, and the Pacific Ocean.
The Southern Ocean extends from Antarctica north to 60 degrees south latitude, which coincides with the Antarctic Treaty region and approximates the Antarctic Convergence. The Southern Ocean is now the fourth largest of the world’s five oceans (after the Pacific Ocean, the Atlantic Ocean, and the Indian Ocean, but larger than the Arctic Ocean).
Note that the Southern Ocean’s inclusion does not recognize this feature as one of the world’s primary oceans by the US Government.
Oceans and shallow seas cover more than two-thirds of the planet, to an average depth of 2½ miles / 3.8 km. The Pacific Ocean alone covers nearly half the globe. The oceans contain about 320 million cubic miles / 1,330 million cubic km of salty seawater, accounting for 97 percent of the water on Earth. Most of this water forms a dark, cold realm deep below the surface, where life is scarce, but the shallow, sunlit waters of coastal seas are some of the world’s richest wildlife habitats.