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In a high emissions future, the world’s strongest ocean current could slow down by 20% by 2050, further accelerating Antarctic ice sheet melting and sea level rise, an Australian-led study has found.
The Antarctic Circumpolar Current – a clockwise current more than four times stronger than the Gulf Stream that links the Atlantic, Pacific and Indian oceans – plays a critical role in the climate system by influencing the uptake of heat and carbon dioxide in the ocean and preventing warmer waters from reaching Antarctica.
Using Australia’s fastest supercomputer and climate simulator, Gadi, located at Access National Research Infrastructure in Canberra, the researchers used climate models to analyse the impact of changing temperature, ice melting and wind conditions on the Antarctic Circumpolar Current.
The results, published in Environmental Research Letters, revealed a clear link between meltwater from Antarctic ice shelves and circumpolar current slowdown, and comes less than a week after another paper anticipated a weakening in vital Atlantic Ocean currents.
What they found suggested a “substantial reconfiguration of Southern Ocean dynamics”, with “far-reaching impacts on global climate patterns, oceanic heat distribution, and marine ecosystems”.
Co-author Assoc Prof Bishakhdatta Gayen, from the University of Melbourne, described the result as “quite alarming”.
He explained that as melting Antarctic ice released cold, fresh water into the ocean, this sank and spread towards the equator. That flow of fresh water changed the density variation in the ocean, a key driver of movement, causing the slowdown.
“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,” Gayen said.
Co-author and climate scientist Dr Taimoor Sohail said the slowdown could lead to a “vicious cycle”, where more warm water reaches the Antarctic shelf accelerating ice melting and further weakening the current.
This could also disrupt ecosystems and food webs, he said, as the oceanic current helps to prevent invasive species – such as rafts of southern bull kelp – from reaching the fragile continent, or redistributed them.
“Concerted efforts to limit global warming – by reducing carbon emissions – will limit Antarctic ice melting, averting the projected slowdown,” Sohail said.
Dr Edward Doddridge, a physical oceanographer at the University of Tasmania who was not involved with the study, said it was significant and surprising, given previous studies had indicated that the northern parts of the Antarctic Circumpolar Current were accelerating due to ocean warming.
Doddridge said it was important to investigate the ways that ocean currents might change, given more than 90% of the extra heat trapped on Earth had been stored in the oceans, which then moved the heat around in ways that affected the climate and weather in different places around the world.
Monash University climate scientist Dr Ariaan Purich, who was not involved with the paper, said dramatic changes were already under way in the oceans around Antarctica.
Fresh water stored in Antarctic ice sheets and shelves was melting at an accelerating rate, she said, and every summer since 2022 – for the first time in recorded history – the extent of sea ice surrounding the continent had dropped below 2m square kilometres.
“We need to know what the ocean is doing and how much heat and carbon the ocean is taking up so that we can better project the climate that we’re experiencing here on land in Australia, and that we can better adapt for that climate,” she said.
