These new discoveries reveal the origins of the most powerful current on Earth

The Antarctic Circumpolar Current is the largest oceanic current on Earth, connecting the Atlantic, Pacific, and Indian Oceans. This current plays a major role in regulating the exchanges of heat, moisture, carbon, and nutrients between the Southern Ocean and the other ocean basins, significantly impacting the concentration of carbon dioxide in the atmosphere and the global climate. Despite its pivotal role in global ocean circulation, climate dynamics, and Antarctic ice stability, when and how this current developed remain questions that have been widely debated for nearly forty years.


The initiation of the Antarctic Circumpolar Current was long thought to be exclusively linked to the opening of the Drake Passage, between South America and the Antarctic Peninsula, and the Tasman Passage, south of Australia. It would have progressively isolated the Antarctic continent from any heat contributions, leading to its glaciation during the Eocene-Oligocene transition, about 34 million years ago.

An international team of scientists, including members from the CNRS Earth & Universe, challenges this theory. The team utilized innovative techniques, such as neodymium isotopes analyzed on fossil fish teeth, and measured the size of grains in marine sediments collected from the Southern Ocean covering the last 31 million years. These new records have identified the period during which the Antarctic Circumpolar Current exhibited circulation and intensity similar to today's, meaning a powerful current that extends from the surface to, almost, the abyssal depths and over a vast area.

This study confirmed that the opening of the Drake and Tasman Passages indeed facilitated the deployment of this current around the continent. However, the true catalysts that enabled it to acquire its current characteristics are the increase in the density contrast between the different water masses present in the Southern Ocean and the intensification of the Westerlies circulating around the white continent.

Scientists have found that these large-scale hydrological and atmospheric changes resulted from the global cooling of Earth's climate and the resulting glaciation of Antarctica during the middle Miocene climatic transition 14 million years ago, that is, 20 million years later than suggested by previous studies. We have thus concluded that it is these climate changes that are responsible for the birth of this current as we know it today.

This study, therefore, raises many fundamental questions concerning the future of this current in the context of climate change, global warming, and the gradual melting of ice in Antarctica.

Reference:
Evangelinos, D., Etourneau, J., van de Flierdt, T. et al.
Late Miocene onset of the modern Antarctic Circumpolar Current. Nat. Geosci. 17, 165-170 (2024).