The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica.
The National Geographic Society recently recognized the Southern Ocean as the new, 5th ocean. The National Geographic is a non-profit scientific and educational organization whose mapping standards are referenced by many atlases and cartographers, but that organization the only one with input? Who decides how many oceans there are?
It's based on recognition by the U.S. Board on Geographic Names, National Oceanic and Atmospheric Administration (NOAA), the International Hydrographic Organization (IHO), general international consensus, and input from organizations like the National Geographic Society.
The Southern Ocean is recognized by the U.S. Board on Geographic Names as the body of water extending from the coast of Antarctica to the line of latitude at 60 degrees South. The National Geographic Society recently concurred. NOAA is onboard as well. While there has been descent from some of the IHO’s 94 members, the rest of the world has adopted the notion that the Southern Ocean is the new, 5th ocean.
The NOAA website addresses the topic in a straightforward way, stating that "there is one global ocean, the vast body of water that covers 71 percent of the Earth," and that, "historically, there are four named oceans: the Atlantic, Pacific, Indian, and Arctic." NOAA also acknowledges that "most countries—including the United States—now recognize the Southern (Antarctic) as the fifth ocean."
National Geographic Society geographer Alex Tait stresses that the waters surrounding Antarctica form a “distinct ecological region defined, by ocean currents and temperatures” and that it's important “from an educational standpoint, as well as from a map-labeling standpoint, to bring attention to the Southern Ocean as a fifth ocean.”