The Southern Ocean is the fourth largest of the five world oceans, yet it is the one that the fewest mariners will ever sail through. Circling the Antarctic continent, its current forms a virtual moat isolating and keeping Antarctica frozen.
Other oceans are bounded by continental landmasses, but the Southern Ocean is defined by the Antarctic Convergence, a subtle band of sea surface temperature changes. This is an irregular boundary varying from 48- to 60-degrees south latitude, where sea surface temperature drops from five to ten degrees Fahrenheit over a distance of 20 to 30 miles. While this may not seem like a big change, it is a very significant gradient within the oceans.
Ship operations are impossible year-round, as sea ice covers roughly 80 percent of the Southern Ocean for the Austral winter and some of the spring and fall. In the summer, roughly 11 percent of the surface remains permanently ice-covered.