Climate crisis: Melting Antarctic ice could weaken ocean’s ‘conveyor belt’, scientists sound alarm

The Antarctic Circumpolar Current (ACC) — the planet’s most powerful ocean current — is weakening as melting ice sheets release vast amounts of freshwater into the Southern Ocean, researchers have found. The slowdown, linked to climate change, could have major implications for sea level rise, ocean warming, and marine ecosystems.

A study by the University of Melbourne and NORCE Norway Research Center, published in Environmental Research Letters, predicts that in a high carbon emissions scenario, the ACC could slow by 20% by 2050.

The influx of freshwater alters ocean properties like density and circulation patterns, with significant consequences. "The ocean is extremely complex and finely balanced. If this current 'engine' breaks down, there could be severe consequences, including more climate variability, with greater extremes in certain regions, and accelerated global warming due to a reduction in the ocean's capacity to act as a carbon sink," said Associate Professor Bishakhdatta Gayen from the University of Melbourne.

More than four times stronger than the Gulf Stream, the ACC connects the Atlantic, Pacific, and Indian Oceans, playing a key role in regulating global heat and carbon exchange. A slowdown could disrupt this "ocean conveyor belt," which moves water, heat, and nutrients around the planet.

Another major concern is the ACC’s role as a natural barrier preventing invasive species from reaching Antarctica. A weaker current increases the risk of species like shrimp, mollusks, and southern bull kelp establishing themselves on the fragile continent, which could disrupt Antarctic food webs and threaten species like penguins.

Dr Taimoor Sohail, a climate scientist at the University of Melbourne, said that even under lower emissions scenarios, the slowdown may still occur if ice melt accelerates as predicted in other studies. "The 2015 Paris Agreement aimed to limit global warming to 1.5°C above pre-industrial levels. Many scientists agree that we have already reached this target, and it is likely to get hotter, with flow-on impacts on Antarctic ice melting," he said.

The study challenges previous research suggesting the ACC might speed up due to increasing temperature differences across latitudes. "Ocean models have historically been unable to adequately resolve the small-scale processes that control current strength," said Associate Professor Gayen. "This model resolves such processes and shows a mechanism through which the ACC is projected to actually slow down in the future."

Further observational and modeling studies are needed to fully understand how the ACC will respond to climate change. However, researchers agree that efforts to curb carbon emissions will be key to slowing ice melt and maintaining the stability of this crucial ocean current.