A decision by the International Hydrographic Organization (IHO) in the spring of 2000 delimited a fifth world ocean - the Southern Ocean - from the southern portions of the Atlantic Ocean, Indian Ocean, and Pacific Ocean. The Southern Ocean extends from the coast of Antarctica north to 60 degrees south latitude which coincides with the Antarctic Treaty Limit. The Southern Ocean is now the fourth largest of the world's five oceans (after the Pacific Ocean, Atlantic Ocean, and Indian Ocean, but larger than the Arctic Ocean).
The IHO ihas updated their official publication, Limits of Oceans and Seas (S-23). The second and most recent edition of this document, which is the global authority on the names and locations of seas and oceans, was produced in 1953. The next (and third) edition of S-23 was released in 2001, and advocated a change with the official addition of the Southern Ocean as the fifth world ocean.
Why the need for a Southern Ocean? According to Commodore John Leech of the IHO, "A great deal of oceanographic research in recent years has been concerned with ocean circulations, first because of El Nino, and then because of a wider interest in global warming...[this research has] identified that one of the main drivers of ocean systems is the 'Southern Circulation,' which sets the Southern Ocean apart as a separate eco-system. As a result the term Southern Ocean has been used to define that huge body of water which lies south of the northern limit. Thinking of this body of water as various parts of the Atlantic, Indian and Pacific Oceans makes no scientific sense. New national boundaries arise for geographical, cultural or ethnic reasons. Why not a new ocean, if there is sufficient cause?"
The Southern Ocean is a body of water that lies between 60 degrees south latitude and the Antarctica coastline. It's coordinates nominally are 65 00 S, 0 00 E, but the Southern Ocean has the unique distinction of being a large circumpolar body of water totally encircling the continent of Antarctica. This ring of water lies between 60 degrees south latitude and the coast of Antarctica, and encompasses 360 degrees of longitude
The total area is about 20.327 million sq km and includes the Amundsen Sea, Bellingshausen Sea, part of the Drake Passage, Ross Sea, a small part of the Scotia Sea, Weddell Sea, and other tributary water bodies. It has a coastline: 17,968 km, and its sea temperatures vary from about 10 degrees Celsius to -2 degrees Celsius.
Despite the demarcation of this "new" ocean, it's likely that the debate over the number of oceans will continue nonetheless. After all, there is but one "world ocean" as all five (or four) oceans on our planet are connected.
Sources: Abstracted from IHO, About.com, CIA FActbook, and other sources.