Background: 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 warmer waters of the north 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, which in turn allows for a greater abundance of animal life. In 2000, the International Hydrographic Organization delimited the waters within the Convergence as a fifth world ocean basin -- the Southern Ocean -- by combining 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 region and which approximates the extent of the Antarctic Convergence. As such, the Southern Ocean is now the fourth largest of the world's five ocean basins (after the Pacific Ocean, Atlantic Ocean, and Indian Ocean). It should be noted that inclusion of the Southern Ocean does not imply US Government recognition of this feature as one of the world's primary ocean basins.

Area
Total: 21.96 million km²
Note: includes 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
Comparative: slightly more than twice the size of the US

Coastline: 17,968 km

Climate: sea temperatures vary from about 10 degrees Celsius to -2 degrees Celsius; cyclonic storms travel eastward around the continent and frequently are intense because of the temperature contrast between ice and open ocean; the ocean area from about latitude 40 south to the Antarctic Circle has the strongest average winds found anywhere on Earth; in winter the ocean freezes outward to 65 degrees south latitude in the Pacific sector and 55 degrees south latitude in the Atlantic sector, lowering surface temperatures well below 0 degrees Celsius; at some coastal points intense persistent drainage winds from the interior keep the shoreline ice-free throughout the winter

Elevation
Highest point: sea level
Lowest point: southern end of the South Sandwich Trench -7,434 m unnamed deep
Mean depth: -3,270 m
Ocean zones: the ocean is divided into three zones based on depth and light level; sunlight entering the water may travel about 1,000 m into the oceans under the right conditions, but there is rarely any significant light below 200 m
Euphotic zone: the upper 200 m (656 ft) is also called 'sunlight' zone; only a small amount of light penetrates beyond this depth
Dysphotic zone: between 200 m (656 ft) and 1,000 m (3,280 ft), and also called the twilight zone; the intensity of light rapidly dissipates as depth increases, and photosynthesis is no longer possible
Aphotic zone: below 1,000 m (3,280 ft) and also called the midnight zone; sunlight does not penetrate to these depths

Natural hazards: huge icebergs with drafts up to several hundred meters; smaller bergs and iceberg fragments; sea ice (generally 0.5 to 1 m thick) with sometimes dynamic short-term variations and with large annual and interannual variations; deep continental shelf floored by glacial deposits varying widely over short distances; high winds and large waves much of the year; ship icing, especially May-October; most of region is remote from sources of search and rescue

Geography
Note: the major chokepoint is the Drake Passage between South America and Antarctica; the Polar Front (Antarctic Convergence) is the best natural definition of the northern extent of the Southern Ocean; it is a distinct region at the middle of the Antarctic Circumpolar Current that separates the cold polar surface waters to the south from the warmer waters to the north; the Front and the Current extend entirely around Antarctica, reaching south of 60 degrees south near New Zealand and near 48 degrees south in the far South Atlantic, coinciding with the path of the maximum westerly winds