The Southern Ocean surrounds the continent of Antarctica. Th e Southern Ocean wasn't an “official” ocean until 2000. Until then, it was usually called the Antarctic Ocean, and was considered a polar region of the other three major oceans. But scientists realized that the winds that blow around the continent of Antarctica are so strong that the surface currents of the Southern Ocean qualify it as its own ocean. Th e Southern Ocean's official boundaries are all the waters that lie south of 60 degrees south latitude.
Th e Southern Ocean is about twice the size of the United States, but it is much smaller than the other three major oceans. It is the coldest ocean on the planet, with average temperatures ranging from 28 to 50 degrees Fahrenheit (-2 to 10 degrees Celsius). In winter, more than half of the ocean is covered with ice and icebergs. Th e Southern Ocean is known for its extreme weather. Because there is no land to block the wind and waves that circle the globe at the southern tip, the winds can reach above 190 miles (306 kilometers) per hour.
Even though the Southern Ocean is cold, it is still full of life. In the spring, blooms of plankton form in the water. Plankton attract krill, which are tiny shrimp-like sea creatures about 1¼ inches (4 centimeters) long. Krill are the favorite food of many ocean creatures, from fish to giant whales. Giant swarms of krill look like huge red patches on the surface of the ocean. They are the first link in a huge food chain that includes fish, seabirds, seals, penguins, and whales.
While the other oceans are defined by the continents that fence them in, the Southern Ocean is defined by a current. Scientists estimate that the Antarctic Circumpolar Current (ACC) was established roughly 34 million years ago, when Antarctica separated from South America.
Bartolomeo Diaz was the first known explorer to have reached the Southern Ocean, when he circumnavigated the Cape of Good Hope in 1487. In 1770, Captain James Cook searched for land in the Southern Ocean but found none, but discovered the prize of Botany Bay, Australia instead.