Southern Ocean

A giant current of water flows all the way around Antarctica. Strong winds push it.

It makes some of the roughest seas in the world.

The Antarctic Circumpolar Current is the only current that goes all the way around our planet. Strong westerly winds drive it, and it connects the Atlantic, Pacific and Indian Oceans. It creates some of the roughest seas in the world.

The current reaches from the surface down to 4,000 meters and can be more than 120 miles (about 190 kilometers) wide. Its water is very cold, from about -1 to 5 °C.

Woods Hole Oceanographic Institution calls the Antarctic Circumpolar Current (ACC) the largest wind-driven current on Earth. The American Meteorological Society's glossary gives its volume transport as about 130 Sv (130 million m³ per second), the largest of all ocean currents, achieved through great depth rather than speed: typical speeds are modest, about 0.1 m/s, but larger in fronts.

The ACC acts as a barrier separating the Southern Ocean from the oceans to the north. Around Antarctica, dense water forms on the continental shelf, especially in the Weddell and Ross Seas, and sinks to spread through the deep ocean as Antarctic Bottom Water, the coldest, deepest water in the ocean.

The Southern Ocean has a very deep crack in the sea floor called a trench.

A deep-diving submarine went down to the bottom, more than 7 kilometers down.

The deepest known point of the Southern Ocean is in the South Sandwich Trench, 7,432 meters down. The Five Deeps Expedition mapped it with sonar and then sent a deep-diving submersible to the spot.

The deepest part of the whole trench, the Meteor Deep, is even deeper. But the trench crosses the 60 degrees south line, and the Meteor Deep lies on the Atlantic side, so the scientists counted it as part of the Atlantic Ocean.

Bongiovanni, Stewart and Jamieson (2021) report the Southern Ocean's deepest point, an unnamed deep south of 60°S in the South Sandwich Trench, as 7,432 ± 13 m by multibeam sonar, at 60.479°S, 25.542°W; a submersible dive verified it as 7,434 ± 3 m.

The trench's overall deepest point, the Meteor Deep at 8,265 ± 13 m, lies within the Atlantic Ocean under the 60°S boundary the authors followed (the Antarctic Treaty and International Hydrographic Organization guidelines), not in the Southern Ocean.

In winter, ice covers much of the sea. Tiny algae live inside the ice, and baby krill eat them.

In spring the ice melts. Then krill eat and eat, and penguins, seals and whales eat the krill.

Much of the Southern Ocean is covered by ice for half the year. Tiny algae get trapped in the ice and grow on its underside, and young krill gather under the ice all winter to feed on them.

When the ice melts in spring, the algae bloom in the sunny, nutrient-rich water. Krill multiply, and some scientists estimate that all the krill around Antarctica weigh more than all the people on Earth. Penguins, seals and whales feed on them.

Woods Hole Oceanographic Institution describes the ocean around Antarctica as one of the most abundant on Earth, with production tied to the seasons. Winter sea ice traps single-celled algae, which also grow on its underside and feed juvenile krill; in spring, melting ice releases them, and with wind-stirred nutrients and intense sunlight they bloom.

Krill, rich in protein and fat, feed penguins, seals and whales; some scientists estimate their total weight exceeds that of the world's human population. WHOI notes that high productivity is confined to the sea-ice edge and a few other areas, and may be changing as the climate warms and sea ice declines.

People visit the Southern Ocean on ships, with guides.

Visitors stay away from the edge of the sea ice and never feed the animals. The weather can change fast.

Most visitors travel by ship to the Antarctic Peninsula between October and April. Guidelines agreed by the Antarctic Treaty countries ask them to be ready for severe, changeable weather and to keep a safe distance from the edge of the sea ice.

Breaking pieces of glacier ice can make dangerous waves. Small boats must adjust their course and speed to avoid disturbing or hitting wildlife, fur seals need extra room (15 to 25 meters where possible), and no one should ever feed the animals.

The Antarctic Treaty Secretariat reports over 100,000 tourists a year, mostly by ship to the Antarctic Peninsula in the October-April season, and says Resolution 4 (2025) updated the General Guidelines for Visitors. The 2021 version it links asks visitors to prepare for severe and changeable weather, keep a safety distance from the sea-ice edge, be vigilant near calving glaciers (falling ice can generate dangerous waves) and not expect a rescue service.

Small boats must regulate course and speed to minimize disturbance and avoid collisions with wildlife; visitors should keep 15-25 m from fur seals where practicable and must not feed wildlife.