Antarctic Circumpolar Current

The Antarctic Circumpolar Current (ACC) is a powerful ocean current that flows clockwise around Antarctica. Also called the West Wind Drift, it is the largest ocean current in the world, moving a huge amount of water. Because there are no landmasses to block it, the ACC circles the entire continent, helping to keep warm waters away from Antarctica and allowing the continent to maintain its massive ice sheet.

This current is very important for marine life. Where the cold Antarctic waters meet warmer subantarctic waters, a zone called the Antarctic Convergence forms. This area brings up nutrients from deep water, feeding lots of tiny plants called phytoplankton. These support small animals like copepods and krill, which in turn feed fish, whales, seals, penguins, albatrosses, and many other species.

Sailors have known about the ACC for centuries. It speeds up travel from west to east but makes it very hard to sail from east to west. Famous stories like Jack London's "Make Westing" and events around the mutiny on the Bounty show how difficult it was for ships trying to go west around Cape Horn. The fastest sailing route in the world, the eastbound clipper route, follows the ACC around three major capes: Cape Agulhas in Africa, South East Cape in Australia, and Cape Horn in South America. The ACC also helps create large circular patterns of water called the Ross and Weddell Gyres.

Structure

The Antarctic Circumpolar Current connects the Atlantic, Pacific, and Indian Oceans, allowing water to move between them. It flows around Antarctica, passing through places like the Drake Passage between South America and the Antarctic Peninsula. Along its path, the current splits and changes direction due to underwater mountains and islands.

The current has three main fronts, or boundaries, including the Subantarctic front, the Polar front, and the Southern ACC front. These fronts help separate different types of water. The ACC is the strongest ocean current, moving a huge amount of water around the globe.

Dynamics

The Antarctic Circumpolar Current is driven by strong westerly winds in the Southern Ocean. Because there are no continents to block it, the current flows freely around Antarctica. The winds push the water, which then moves in a way influenced by Earth's rotation.

The current flows at a speed of about 4 kilometers per hour. It also changes over time, influenced by patterns like the Antarctic Circumpolar Wave and the Antarctic oscillation, which affect winds and climate in the southern hemisphere.

Main article: Antarctic Circumpolar Wave
Main article: Antarctic oscillation

Formation

The Antarctic Circumpolar Current likely began around the time when Antarctica became isolated from other lands. This happened when water pathways, like the Tasmanian Passage and the Drake Passage, opened up. These changes helped cool the planet and contributed to Antarctica becoming icy. Scientists think the openings of these passages happened millions of years ago, and they played a big role in shaping Earth’s climate.

Phytoplankton

Antarctic sea ice changes with the seasons, shrinking in February–March and growing in August–September. As the ice melts, it brings nutrients from deep water to the surface, helping tiny plants called phytoplankton grow. These phytoplankton blooms feed many sea animals, including whales, seals, and birds.

Phytoplankton growth is influenced by sunlight and nutrients like iron. The Antarctic Circumpolar Current helps support these blooms, especially with diatoms, a type of phytoplankton. These tiny plants play an important role in taking carbon from the air, helping to keep our planet healthy.

Studies

In May 2008, 19 scientists explored the Antarctic Circumpolar Current to understand how it affects the Southern Ocean’s effects of climate change. This current connects the Atlantic, Indian, and Pacific Oceans, moving a huge amount of water—up to 150 times more than all the world’s rivers combined. It plays a big role in shaping both the climate and marine life.

The current also helps protect old wooden ships, like Ernest Shackleton’s Endurance, by stopping creatures called “ship worms” from damaging them. Recent reports suggest the current might be getting weaker, which could change ocean patterns and affect the climate in many places.