Earth’s most powerful ocean current played a decisive role in reshaping the planet’s climate millions of years ago, according to new scientific research that challenges long-held assumptions about how global cooling began. The Antarctic Circumpolar Current (ACC), which flows uninterrupted around Antarctica, is the strongest ocean current on Earth.
Carrying more than 100 times the combined flow of all rivers worldwide, it acts as a major force in regulating global temperatures. Unlike other currents, it is not blocked by continents, allowing it to circulate freely and influence climate systems across the planet.
A study published in the Proceedings of the National Academy of Sciences examined how this vast current first formed. Researchers found that the opening of ocean passages alone was not enough to immediately generate a powerful ACC, contradicting earlier theories that linked these geological changes directly to rapid global cooling.
Gradual climate shift, not sudden change
The research centers on a major climate transition about 34 million years ago during the Oligocene Epoch. Before this period, Earth experienced relatively warm conditions with little ice coverage. As temperatures declined, large ice sheets began forming across Antarctica, marking a significant shift in the planet’s climate system.
New research shows how the Antarctic Circumpolar Current formed over millions of years, driving global cooling and influencing today’s climate system. pic.twitter.com/22Gpx5tSv7
— Tom Marvolo Riddle (@tom_riddle2025) April 7, 2026
At the same time, tectonic activity created ocean gateways between Antarctica, South America and Australia. Scientists had previously believed these openings triggered the formation of the ACC and accelerated cooling. However, the new findings indicate the process unfolded more slowly and involved multiple factors.
Strong westerly winds emerged as a key driver in shaping the current. The Tasman Gateway, located between Antarctica and Australia, proved particularly important. Researchers reported that the ACC only became a continuous and powerful flow after Australia drifted farther north, allowing winds to pass unobstructed through the gateway.
Winds, ocean flow, and carbon changes
In its early stages, the ACC behaved differently from its modern form. It did not fully encircle Antarctica and produced uneven ocean circulation. Strong currents developed in parts of the Atlantic and Indian Oceans, while the Pacific region remained comparatively stable.
As the current strengthened, it began isolating Antarctica from warmer northern waters. This separation contributed to further cooling, enabling ice sheets to expand and stabilize over time. The process ultimately helped shift Earth into a cooler climate system with permanent polar ice.
Researchers also found that the development of the ACC altered how carbon moved through the oceans. Increased circulation improved the ocean’s ability to absorb carbon dioxide, reducing greenhouse gas levels in the atmosphere and supporting long-term cooling trends associated with the Cenozoic Ice Age.
Using advanced climate and ice-sheet models, scientists reconstructed these ancient changes to better understand interactions between oceans, atmosphere, and ice. The findings offer valuable insights into modern climate systems, particularly in the Southern Ocean, and may improve future climate predictions.