Melting Antarctic ice slows ocean flows – 03/29/2023 – Environment

Accelerating melting of Antarctic ice is severely reducing water movement in the world’s oceans and could have a disastrous impact on global climate, the marine food web and even the stability of ice shelves, new research has revealed.

The “reverse circulation” of the oceans, caused by the movement of denser water towards the bottom of the sea, helps circulate heat, carbon, oxygen and vital nutrients around the planet.

But Antarctica’s deep ocean currents could slow by 40% by 2050, according to a study published Wednesday in the journal Nature.

“It’s shocking to see this happen in such a short time,” said Alan Mix, a paleoclimatologist at Oregon State University and co-author of the most recent assessments by the Intergovernmental Panel on Climate Change (IPCC), who was not involved in the study. “The process seems to be starting now. It’s news that needs to make headlines.”

As temperatures rise, fresh water from melting Antarctic ice enters the ocean, reducing the salinity and density of surface water and reducing downward flow toward the sea floor.

Past research has looked at what might happen with reversed circulation in the North Atlantic — the mechanism behind the end-of-the-world scenario that would see Europe experience Arctic cooling as heat transport weakens. But the circulation of Antarctic water at the bottom of the sea had not been similarly studied.

Scientists used 35 million hours of computing over two years to analyze a series of models and simulations stretching back to the middle of this century, concluding that deep water circulation in Antarctica will weaken twice as fast as it declines in the Atlantic. north.

“These are huge volumes of water. And they are parts of the ocean that have been stable for a long time,” said oceanographer Matthew England, from the University of New South Wales and co-author of the study, in a news briefing.

THE BASIS OF THE FOOD CHAIN

The effect on global ocean water circulation resulting from melting ice has not yet been factored into the complex models used by the IPCC to describe future climate change scenarios, but it will be considerable, England said.

Reverse ocean circulation allows nutrients to rise from the sea floor. The Southern Ocean supports about three-quarters of global production of phytoplankton, the base of the food chain, said a second study co-author, Steve Rintoul.

“If we slow down the sinking process near Antarctica, we slow down the entire circulation and thereby also reduce the amount of nutrients returned from the depths of the sea to the surface,” said Rintoul, a member of the Australian Commonwealth Scientific and Industrial Research Organization. (CSIRO).

The study’s findings also suggest that the ocean will not be able to absorb as much carbon dioxide, as its upper layers become more stratified, which will leave more CO2._two In the atmosphere.

The study showed that warm water intrusions on the West Antarctic Ice Shelf will increase, but did not examine how this might create a feedback effect and drive further melting.

“The study doesn’t cover catastrophic scenarios,” said Mix. “In that sense, it’s actually quite conservative.”

^{Translated by Clara Allain}