How Tectonic Shifts and Winds Created Earth’s Most Powerful Ocean Current

The Antarctic Circumpolar Current, the planet’s most powerful ocean current, may have formed only once Earth’s continents shifted and winds aligned with newly opened ocean pathways, according to a study published in the Proceedings of the National Academy of Sciences of the United States of America.

Today, this current transports over 100 times the volume of water carried by all of Earth’s rivers combined. Crucially, it shields the Antarctic Ice Sheet from heat originating in lower latitudes, helping regulate the continent’s climate.

“It’s very interesting to learn more about this current, how it developed, and what role it played in the climate change that was happening at that time,” said Hanna Knahl, a paleoclimatologist and doctoral student at the Alfred-Wegener-Institut in Germany, and lead author of the study.

The Birth of the Antarctic Circumpolar Current

Around 34 million years ago, Earth experienced a major climatic transition known as the Eocene-Oligocene transition. During this period, atmospheric carbon dioxide levels dropped, and global temperatures cooled.

At the same time, tectonic plates in the Southern Ocean shifted apart, opening and deepening critical ocean gateways such as the Tasmanian Gateway and the Drake Passage. These gateways separate Antarctica from Australia and South America, respectively.

For years, scientists theorized that the realignment of these waterways, combined with the influence of westerly winds, could have directed ocean water flow and triggered the formation of the Antarctic Circumpolar Current.

“The exact position of the westerly winds and their relative position to the [ocean] gateways have to click together.”

To test this hypothesis, Knahl and her team simulated the conditions of the early Oligocene Southern Ocean using a coupled model. The model incorporated ocean dynamics, atmospheric and wind patterns, temperatures, ice sheet growth, and precipitation. The researchers then compared these simulations with data from Antarctic sediment cores and ocean floor scans.

The results confirmed that westerly winds were essential for the Antarctic Circumpolar Current to form.

“The exact position of the westerly winds and their relative position to the [ocean] gateways have to click together,”

Joanne Whittaker, a marine geophysicist at the University of Tasmania who was not involved in the study, coauthored a 2015 study proposing that westerly wind alignment influenced the current’s formation. She noted that Knahl’s research presents a more advanced model of the early Oligocene Southern Ocean and represents a significant step forward in understanding the current’s origins.

“They did a really nice job of taking a range of different people’s work and linking it all together.”

Implications for Past and Future Climate Models

“If you can have a model that works in the past, it’s going to give you confidence that it’s going to work for the future, as well,” Whittaker said.

Scientists frequently use Earth’s past behavior to predict how current systems may respond to future climate changes. By refining models of ancient ocean currents, researchers can improve their understanding of how similar mechanisms might operate today and in the coming decades.