Sydney, March 3 The Antarctic Circumpolar Current (ACC), the world's strongest ocean current, is currently being slowed by melting Antarctic ice sheets, which could lead to sea level rise and ocean warming, and change life for fish and animals such as Antarctic penguins, a study said on Monday.
The ACC, more than four times stronger than the Gulf Stream, is a crucial part of the world's "ocean conveyor belt," which moves water around the globe -- linking the Atlantic, Pacific and Indian Oceans -- and is the main mechanism for the exchange of heat, carbon dioxide, chemicals and biology across these ocean basins.
However, the current has been slowing by around 20 per cent by 2050 in a high carbon emissions scenario, according to researchers from the University of Melbourne and NORCE Norway Research Centre.
This influx of fresh water into the Southern Ocean, caused by melting Antarctic ice sheets, is expected to change the properties, such as density or salinity, of the ocean and its circulation patterns, said the study published in Environmental Research Letters, which shows the impact of ice melting and ocean warming on the ACC is more complex than previously thought.
Researchers analysed a high-resolution ocean and sea ice simulation of ocean currents, heat transport and other factors to diagnose the impact of changing temperature, saltiness and wind conditions.
"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 University of Melbourne fluid mechanist Bishakhdatta Gayen.
The ACC works as a barrier to invasive species, like rafts of southern bull kelp that ride the currents, or marine-borne animals like shrimp or molluscs, from other continents reaching Antarctica, the study said, adding that as the ACC slows and weakens, there is a higher likelihood such species will make their way onto the fragile Antarctic continent, with a potentially severe impact on the food web, which may, for example, change the available diet of Antarctic penguins.
Australia's fastest supercomputer and climate simulator, GADI, has been used in the research, with a research team based at the University of New South Wales finding that the transport of ocean water from the surface to the deep may also slow in the future, Xinhua news agency reported.
University of Melbourne's climate scientist Taimoor Sohail said many scientists agree the 1.5-degree target, a limit set in the 2015 Paris Agreement for the rise of temperatures against pre-industrial levels, has already been reached, and "it is likely to get hotter, with flow-on impacts on Antarctic ice melting."
Sohail called for concerted efforts to limit global warming by reducing carbon emissions to limit Antarctic ice melting, averting the projected ACC slowdown.
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