Rapidly melting Antarctic ice could affect the oceans for ‘centuries’

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Scientists warn that deep ocean water currents from Antarctica could decline by 40 percent by 2050, threatening the collapse of circulation critical to planetary systems.

Rapidly melting Antarctic ice is dramatically slowing water flow through the world’s oceans and could have a disastrous effect on the world’s climate, marine food chain and even the stability of ice shelves, new research says.

The oceans’ “overturning circulation” — driven by the movement of denser water to the seafloor — helps deliver heat, carbon, oxygen and essential nutrients around the world.

However, deep ocean water currents from Antarctica could decline by 40 percent by 2050, according to a study published Wednesday in the journal Nature that warned of effects that would last “for centuries.”

“It’s amazing to see that happening so quickly,” said Alan Mix, a paleoclimatologist at Oregon State University and co-author of the latest Intergovernmental Panel on Climate Change (IPCC) assessments, who was not involved in the study. research.

“It seems to be getting underway now. That is front page news.”

If the model is true, deep-sea currents “will be on a trajectory that appears to be headed for collapse,” said Matthew England, a climate professor at the University of New South Wales (UNSW), who coordinated the study.

View of a glacier at Chiriguano Bay in the South Shetland Islands, Antarctica on Nov. 07, 2019. (Photo by Johan ORDONEZ/AFP)
View of a glacier at Chiriguano Bay in the South Shetland Islands, Antarctica [File: Johan Ordonez/AFP]

‘Profound Effects’

As temperatures rise, fresh water from Antarctica’s melting ice enters the ocean, decreasing the salinity and density of surface water and decreasing downdrafts to the sea floor.

While past research has looked at what might happen to a similar overturning circulation in the North Atlantic – the mechanism behind a doomsday scenario where Europe would suffer an Arctic explosion while heat transport falters – less has been done on the Antarctic soil water circulation.

Scientists relied on about 35 million hours of computation over two years to run through a variety of models and simulations until the middle of this century, finding deep-water circulation in Antarctica could be declining twice as fast as in the North Atlantic.

UNSW emeritus professor John Church, who was not involved in the study, said there were many uncertainties about the impact of declining deep ocean circulation.

“But it seems almost certain that continuing on a path of high greenhouse gas emissions will lead to even greater impacts on the ocean and the climate system,” Church said.

“The world urgently needs to drastically reduce our emissions to get off the high-emissions path we are currently on.”

The research team included lead author Qian Li of the Massachusetts Institute of Technology and co-authors from the Australian National University and Australia’s Commonwealth Scientific and Industrial Research Organization (CSIRO).

‘Disaster Scenarios’

The effect of meltwater on global ocean circulation has not yet been accounted for in the complex models the IPCC uses to describe future climate change scenarios, but it will be significant, England said.

Tilting the ocean allows nutrients to move up from the bottom, with the Southern Ocean supporting about three-quarters of global phytoplankton production, the base of the food chain, said a second study co-author Steve Rintoul.

“If we slow down the sinking near Antarctica, we’re slowing down the entire circulation and also reducing the amount of nutrients that are returned to the surface from the deep ocean,” said Rintoul, a fellow at CSIRO.

The study’s findings also suggest that the ocean would not be able to absorb as much carbon dioxide if the upper layers became more stratified, leaving more CO2 in the atmosphere.

The study showed that warm water intrusion into the western Antarctic ice shelf would increase, but it didn’t look at how this could create a feedback effect and cause even more melting.

“It doesn’t include the disaster scenarios,” Mix said. “It’s actually kind of conservative in that sense.”



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