The Antarctic Circumpolar Current carries more than 100 times as much water as all the world's rivers combined. It reaches from the ocean's surface to its bottom and 2,000 kilometers across, connecting the three oceans. It also plays a key role in regulating global climate.
It's the Antarctic Circumpolar Current—the world's most powerful, consequential mover of water, and has been speeding up. But could it amplify Earth's warming's effects?
Gaining speed in warm years
In a new study, published (open-access) in the journal Nature, an international research team found evidence that the current could speed up the loss of Antarctica's ice, increase sea levels, and possibly affect the ocean's ability to absorb carbon from the atmosphere.
The team charted the ACC's relationship to climate over the last 5.3 million years. Their key discovery: its current has been gaining speed in warm years, suggesting that today's speedup will continue as human-induced warming proceeds.
"This is the mightiest and fastest current on the planet. It is arguably the most important current of the Earth climate system," said study coauthor Gisela Winckler, a geochemist at Columbia University's Lamont-Doherty Earth Observatory who co-led the sediment sampling expedition.
Raising global sea levels by about 190 feet
The study "implies that the retreat or collapse of Antarctic ice is mechanistically linked to enhanced ACC flow, a scenario we are observing today under global warming," she said.
Currently much of the West Antarctic Ice Sheet is frozen to land that is below sea level, so it is highly susceptible to invasion by warm ocean waters. Were it to melt entirely, it would raise global sea levels by about 190 feet.
Holding back the vast interior glaciers
Scientists have observed that winds over the Southern Ocean have increased in strength about 40% in past 40 years. Among other things, this has speeded the ACC and energized large-scale eddies within it that move relatively warm waters from the higher latitudes toward Antarctica's huge floating ice shelves, which hold back the even vaster interior glaciers.
Their findings provide geological evidence in support of further increasing ACC flow with continued global warming, the researchers write in their paper. "If true, a future increase in ACC flow with warming climate would mark a continuation of the pattern observed in instrumental records, with likely negative consequences."
Citation: Lamy, F., Winckler, G., Arz, H.W. et al. Five million years of Antarctic Circumpolar Current strength variability. Nature 627, 789–796 (2024). https://doi.org/10.1038/s41586-024-07143-3 (open access)