Earth’s strongest ocean current played a key role in transforming the planet’s climate millions of years ago, according to new research.
The Antarctic Circumpolar Current (ACC) circles Antarctica and carries more than 100 times the combined flow of all the world’s rivers. It moves freely around the continent without being blocked by land, making it one of the most powerful drivers of global climate.
The study, published in Proceedings of the National Academy of Sciences, explores how this massive current first developed. Researchers found that the opening of ocean passages alone did not immediately create a strong ACC, challenging earlier theories.
A climate turning point
The research focuses on a major shift about 34 million years ago during the Oligocene Epoch. Before this time, Earth had a warmer climate with limited ice. As temperatures dropped, large ice sheets began forming across Antarctica.
At the same time, tectonic movements opened ocean gateways between Antarctica, South America, and Australia. Scientists had long believed these openings triggered the ACC and drove global cooling. The new findings suggest the process was more gradual.
Winds and seaways shaped the current
Researchers found that strong westerly winds were essential to the current’s development. The Tasman Gateway played a critical role.
Lead author Hanna Knahl of the Alfred Wegener Institute said the ACC only became a continuous, powerful flow after Australia moved farther away from Antarctica. This shift allowed winds to pass directly through the gateway.
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
Before that, ocean circulation remained uneven. Strong currents developed in parts of the Atlantic and Indian Oceans, while the Pacific sector stayed relatively calm.
The early system behaved differently
In its early stages, the ACC did not form a full loop around Antarctica. Its influence on the climate was weaker and less stable than today. As the current strengthened, it began to isolate Antarctica from warmer northern waters. This led to further cooling and allowed ice sheets to expand and stabilize.
Researchers say this process helped shift Earth from a warm climate into a cooler system with permanent polar ice.
Carbon and long-term cooling
The formation of the ACC also changed how carbon moved through the oceans. According to Johann Klages, the current increase in the ocean’s ability to absorb carbon dioxide.
This likely reduced greenhouse gas levels in the atmosphere and contributed to the start of the Cenozoic Ice Age, which continues today.
Lessons for today’s climate
The study used advanced climate and ice sheet models to simulate ancient conditions. Co-author Gerrit Lohmann said these models help scientists better understand how oceans, atmosphere, and ice interact.
Researchers say these insights are important for interpreting modern changes in the Southern Ocean and improving future climate predictions.
The findings show that even Earth’s strongest ocean current developed through a combination of winds, shifting continents, and long-term climate feedback.
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