A report on ocean currents in Antarctica heading towards collapse

  • by Tom Housden
  • BBC News, Sydney

A new report warns that the rapid melting of Antarctic ice is causing a significant slowdown in deep ocean currents and could have a catastrophic impact on climate.

A team of Australian scientists says the deep water flows that drive ocean currents could drop by 40% by 2050.

Currents carry vital heat, oxygen, carbon and nutrients around the world.

Previous research suggests that a slowdown in the North Atlantic Current may be causing Europe to cool.

The study, published in the journal Nature, also warns that the slowdown may reduce the ability of the oceans to absorb carbon dioxide from the atmosphere.

The report shows how Earth’s network of ocean currents is driven in part by the downward movement of cold, dense, salty water toward the seafloor near Antarctica.

But as fresh water from the ice sheet melts, sea water becomes less salty and dense, and downward movement slows.

Scientists say deep ocean currents, or “fluctuations,” in the northern and southern hemispheres have been relatively stable for thousands of years, but are now being disrupted by a warming climate.

“Our models show that if global carbon emissions continue at the current rate, the Antarctic reversal will slow by more than 40 per cent in the next 30 years – and on a trajectory that appears to be heading for collapse,” said Professor Matthew England, lead study author of the study. .

As ocean circulation slowed, water at the surface quickly reached its carbon-absorbing capacity and was then not replaced by carbon-unsaturated water from greater depths, explained Dr. Adele Morrison, who contributed to the report.

A 2018 Atlas study found that the Atlantic circulation system was weaker than it had been in more than 1,000 years, and that it had changed dramatically in the past 150.

It suggested that changes in the conveyor-belt-like Atlantic overturning circulation (Amoc) could cool the ocean and northwestern Europe, and affect deep-sea ecosystems.

A dramatic portrayal of the Amok closure was featured in the 2004 climate disaster film The Day After Tomorrow.

But Dr Morrison said the slowdown in the southern overturning would have a bigger impact on marine ecosystems and Antarctica itself.

“The overturning brings nutrients that sink to the bottom when organisms die…to resupply the global ecosystem and fisheries,” she told the BBC.

“The other, bigger effect it could have is feedback on how much Antarctica will melt in the future. And when that upturn slows, it opens a pathway for warmer waters that could cause increased melting, which would act as an additional feedback, causing more Melting water in the ocean and slowing that circulation even further.”

The scientists spent 35 million computing hours over two years producing their models, which suggests that circulation of deep waters in the Antarctic could slow twice the rate of decline in the North Atlantic.

“It looks like he’s on the move now. This is major news,” he told Reuters.

England said the impact of Antarctic meltwater on ocean currents had not been factored into the IPCC’s models of climate change, but would be “significant”.

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