Rapid melting of Antarctic ice is dramatically slowing deep ocean currents and could have catastrophic effects on climate, a new report warns. – writes the BBC science department.
A team of Australian scientists says the deep-water currents that drive ocean currents could drop by 40% by 2050.
Currents transport vital heat, oxygen, carbon and nutrients around the world.
Previous research suggests that a slowdown in the North Atlantic Current could cause Europe to cool off.
The study, published in the journal Nature, also warns that the slowdown could reduce the ocean’s ability to absorb carbon dioxide from the atmosphere.
The report shows that Earth’s network of ocean currents is driven in part by the movement of cold, dense salt water toward the seafloor near the South Pole.
But as fresh water from the ice sheet melts, sea water becomes less salty and less dense, and downward motion slows.
These deep ocean currents in the northern and southern hemispheres have been relatively stable for hundreds of years, but are now being disrupted by a warming climate.
Our models show that if global carbon emissions continue at current rates, the Antarctic flow will slow by more than 40% over the next 30 years. – as a result of a path that seems to be heading towards collapse. “If the oceans had lungs, it would have one,” said lead author of the study Professor Matthew England, an oceanographer at the University of New South Wales in Sydney.
Dr. Adele Morrison, who contributed to the report, explained that as ocean circulation slows, surface water quickly reaches its capacity to absorb carbon and is then not replaced by carbon-depleted water from greater depths.
A 2018 Atlas study found that the Atlantic circulation system is weaker than it has been in more than 1,000 years and has changed dramatically in the past 150 years.
This is indicated by the fact that the conveyor belt-like Amoc (Atlantic Meridian Inversion Circulation) may cool the ocean and northwestern Europe and affect deep-sea ecosystems.
An exaggerated portrayal of Amoc’s closure was shown in 2004, in the 2004 disaster film Holnapután.
But Dr Morrison said shutting down the southern flow would have more than just an impact on marine ecosystems and Antarctica itself. The flow will bring up the nutrients that sank to the bottom when the organism died…to replenish nutrients for the global ecosystem and fishermen. Another big consequence could be feedback on how much Antarctica will melt in the future.
When the flow slows, it gives way to warmer water that can increase melt, which can be another feedback, causing more meltwater in the ocean and slowing circulation even further.
Scientists’ models show that the circulation of deep waters in the Antarctic could be twice the rate of decline in the Arctic.
Professor England said the impact of Antarctic meltwater on ocean currents had not yet been factored into IPCC climate change models, but was being factored into it.
(Source: BBC: https://www.bbc.com/)
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