Melting Antarctic ice sheets are slowing Earth’s strongest ocean current: ‘There could be severe consequences’

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Melting ice sheets are slowing the world’s strongest ocean current, researchers said Monday.

An influx of fresh water from the melting sheets is changing the properties of the ocean and its circulation patterns, altering the water’s salinity which determines the density of the water. Freshwater is less dense than saltwater, interrupting the natural sinking of the denser water that helps to power ocean currents.

Also driven by temperature and wind, ocean currents help to regulate the planet’s climate, transporting warm and cold water around the planet. They’re also critical for marine life, redistributing oxygen and nutrients. But, slowing currents will come with consequences on land and in the ocean, like sea level rise and ocean warming.

“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,” University of Melbourne Associate Professor Bishakhdatta Gayen said in a statement.

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Gayen was one of the researchers who reported the impact to the Antarctic Circumpolar Current. Findings from the university and NORCE Norway Research Centre were published on Monday in the journal Environmental Research Letters.

They say that the largest wind-driven current on Earth — which is the only current that moves around the planet and connects the Atlantic, Pacific, and Indian Oceans — could slow by around 20 percent by 2050 in a high carbon emissions scenario.

Should it slow and weaken, its role as a barrier to invasive species will be tested, with a potentially severe impact on the food web that could change the available diet for Antarctic penguins

To reach these conclusions, they analyzed a simulation of ocean currents, ocean heat transport, and other factors to “diagnose the impact of changing temperature, saltiness and wind conditions.” using Australia’s fastest supercomputer and climate simulator, a team at the University of New South Wales found that the transport of ocean water from the surface to the deep – the colder and saltier water sinks – may also slow.

“The 2015 Paris Agreement aimed to limit global warming to 1.5 degrees Celsius above pre-industrial levels. Many scientists agree that we have already reached this 1.5 degree target, and it is likely to get hotter, with flow-on impacts on Antarctic ice melting,” climate scientist Dr. Taimoor Sohail said.

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The research comes as other scientists have warned about the possible collapse of other critical ocean circulation, and as the world’s ice sheets continue to dwindle. Earlier this month, scientists said that the Greenland Ice Sheet – the world’s second largest body of ice – is cracking open quicker than ever before.

Ultimately, the authors said that the impact of ice melting and ocean warming on the current is more complex than previously believed. And, they said that their research contrasts with other previous studies that suggest it may be accelerating because of steeper temperature differences in different latitudes of the ocean caused by climate change.

“Ocean models have historically been unable to adequately resolve the small-scale processes that control current strength. This model resolves such processes, and shows a mechanism through which the ACC is projected to actually slow down in the future,” Gayen said. “However, further observational and modelling studies of this poorly-observed region are necessary to definitively discern the current’s response to climate change.”