Antarctic Circumpolar Current - Earth's largest ocean current 

The Antarctic Circumpolar Current (ACC) is the largest ocean current on Earth. It flows around Antarctica, connecting all three major basins of the global ocean (Atlantic, Pacific and Indian).  Thus, the Antarctic Circumpolar Current regulates the transport of heat, moisture, carbon and nutrients between the Southern Ocean and the low-latitude regions, playing a vital role in global climate through its strong influence on the global overturning circulation, ocean heat and CO₂ uptake.

Despite its pivotal role in global ocean circulation, climate dynamics, and Antarctic ice sheet stability, the when and how the Antarctic Circumpolar Current reached its modern characteristics have fueled debate for over four decades. Unraveling this knowledge is crucial for comprehending the Antarctic Circumpolar Current response to ongoing global climate warming and its influence on the Antarctic ice sheet.

Until now, it has been considered that the onset of the Antarctic Circumpolar Current was linked to the opening and deepening of Southern Ocean Gateways (Drake Passage, Tasmanian Gateway), triggering thermal isolation of Antarctica, which culminated with continental-scale Antarctic ice sheet expansion during the Eocene-Oligocene Transition (~34 million years ago).

Unraveling the history of the ACC in the past

In our article “Late Miocene onset of the modern Antarctic Circumpolar Current” we investigated legacy sediments from the Deep Sea Drilling Project and Ocean Drilling Program in the Southern Ocean. The locations from where the sediments were retrieved have been under the influence of the Antarctic Circumpolar Current for the past 31 million years.

Through an innovative approach that combines neodymium isotopes analysis on fossilized fish teeth and fish bones to assess the influence of various water masses on the deep ocean, along with grain size sorting in response to hydrodynamic processes, we successfully pinpointed the era when the Antarctic Circumpolar Current became a strong, continuous deep current, resembling today's conditions.

Our new findings

Our study reveals that the opening and deepening of the Southern Ocean Gateways preconditioned the development of a circumpolar current system, but the true catalyst for the onset of the modern Antarctic Circumpolar Current was the enhanced density contrast and the intensified Southern Westerly Winds across the Southern Ocean. These changes were driven by the expansion of Antarctic Ice Sheet and sea ice following the Middle Miocene Climate Transition (~14 million years ago).

“Our findings fundamentally change how we view the interplay between the Antarctic Circumpolar Current and Antarctica's ice sheets throughout Earth’s history. As we face today's climate challenges, understanding this interaction becomes more crucial than ever.”

For more details see our article: https://www.nature.com/articles/s41561-023-01356-3