I.

Introduction

Southern Ocean, fourth largest of the world’s five oceans. The Pacific Ocean, Atlantic Ocean, and Indian Ocean are larger, and the Arctic Ocean is smaller.

II.

Boundaries and Size

The Southern Ocean is generally described as extending from the coast of Antarctica north to latitude 60° south (just south of the southern tip of South America). This latitude approximates the location of the Antarctic Convergence, an ocean zone where cold, northbound Antarctic surface waters sink below warmer sub-Antarctic waters. This zone spans the globe and creates the unique waters and ecosystem of the Southern Ocean.

The Southern Ocean encompasses roughly 20.3 million sq km (7.8 million sq mi) in area, slightly more than twice the size of the United States. Its greatest depth measures 7,235 m (23,737 ft) below sea level in the South Sandwich Trench. The Southern Ocean includes Amundsen Sea, Bellingshausen Sea, Ross Sea, Weddell Sea, and part of Drake Passage.

III.

Geologic Formation and Structural Features

Geologically the Southern Ocean is the youngest of the world’s oceans. It formed around 30 million years ago as Antarctica and South America moved apart. This process is known as continental drift or the theory of plate tectonics. The separation of South America and Antarctica created Drake Passage, the narrowest point in the Southern Ocean located between South America at Cape Horn and the Antarctic Peninsula.

The Southern Ocean is unique in not having a basin defined by land masses at its northern boundary. Its southern boundary is formed by the submerged border of Antarctica, a border narrow and deep due to the massive weight of the Antarctic Ice Sheet depressing the crust. The Kerguelen Plateau—an underwater volcanic ridge that erupted roughly 97 million years ago—is a significant structural feature situated between the Indian and Southern oceans. This area of thick ocean crust is one of the largest undersea plateaus, extending more than 2,200 km (more than 1,350 mi).

The Southern Ocean contains many ice shelves, floating platforms of ice that attach to the coast. The two largest are the Filchner-Ronne Ice Shelf and the Ross Ice Shelf. The Ross Ice Shelf is the world’s largest, extending up to 450 km (280 mi) from the Antarctic shore.

IV.

Islands

The area closely surrounding the Antarctic Peninsula is particularly rich in islands including the South Orkney Islands and the South Shetland Islands. In Bransfield Strait lies Deception Island, the horseshoe-shaped summit of a mostly submerged volcano where two eruptions in the 19th century destroyed scientific stations. The Balleny Islands are located outside the Ross Sea. Roosevelt Island lies in the Ross Sea Ice Shelf and Berkner Island is located in the Filchner-Ronne Ice Shelf.

V.

Temperatures, Currents, and Wind Systems

The water temperature of the Southern Ocean varies from -2°C to 10°C (28°F to 50°F). The ocean’s main current is the Antarctic Circumpolar Current (ACC), also known as the West Wind Drift. The ACC is the strongest current system in the world, and the only one that travels the entire distance around the earth. It flows from west to east and moves roughly 130,000,000 cubic m (4,590,000,000 cubic ft) of water per second through Drake Passage, about 100 times the flow of all the world’s rivers combined. Prevailing westerly winds drive the ACC. These winds blow unhindered by any landmass, causing some of the roughest waters known. Sailors refer to the notorious “roaring forties,” “furious fifties,” and “screaming sixties” as they travel through these latitudes.

VI.

Marine Resources

Oil and gas fields likely exist on the continental margin of Antarctica. Mineral resources include manganese, sand, and gravel. Marine life is plentiful in the Southern Ocean. Phytoplankton proliferates during the extended daylight hours of the summer months. These free-floating plants provide food for enormous populations of krill, tiny shrimplike crustaceans. Fish, squid, seals, whales, and penguins feed on the krill.