Southern Ocean

The Southern Ocean is the most recently recognized of the world's five oceans, the band of cold water that rings Antarctica below roughly 60 degrees south. Covering about 20.3 million square kilometers (7.8 million square miles), it was long treated as merely the southern fringes of the Pacific, Atlantic, and Indian oceans. National Geographic formally recognized it as a distinct ocean in 2021, acknowledging what oceanographers had long argued: the waters here are ecologically and physically their own.

What sets it apart is the Antarctic Circumpolar Current, the most powerful current on Earth, which flows clockwise around the continent unobstructed by any land. This vast conveyor isolates Antarctica, keeps it frozen, and links the other oceans into a single global circulation. The Southern Ocean reaches its deepest, about 7,235 meters (23,737 feet), in the South Sandwich Trench. Its frigid, nutrient-rich waters teem with krill that feed whales, seals, penguins, and seabirds.

Because its current draws cold water and carbon down into the deep sea, the Southern Ocean plays an outsized role in regulating global climate, absorbing a large share of the heat and carbon dioxide humans have added to the atmosphere. Changes here — warming water, shifting ice, and stressed krill stocks — ripple through the entire planet's ocean system.

• Antarctica
  The frozen continent at the bottom of the world encircles
• Atlantic Ocean
  The world's second-largest ocean and great highway of history merges with
• Indian Ocean
  The world's third-largest and warmest ocean merges with
• Pacific Ocean
  Earth's largest and deepest ocean merges with