The Rising Influence of Rising Affluence

[Biowatch]

Slowing ocean current caused by melting Antarctic ice could have drastic climate impact, study says

https://www.theguardian.com/science/2023/may/25/slowing-ocean-current-caused-by-melting-antarctic-ice-could-have-drastic-climate-impact-study-says

[Could bring a new meaning to the phrase “climate change.’]

A major global deep ocean current has slowed down by approximately 30% since the 1990s as a result of melting Antarctic ice, which could have critical consequences for Earth’s climate patterns and sea levels, new research suggests.

Known as the Southern Ocean overturning circulation, the global circulation system plays a key role in influencing the Earth’s climate, including rainfall and warming patterns. It also determines how much heat and carbon dioxide the oceans store.

Scientists warn that its slowdown could have drastic impacts, including increasing sea levels, altering weather patterns and depriving marine ecosystems of vital nutrients.

“Changes in the overturning circulation are a big deal,” said the study’s co-author, Dr Steve Rintoul, an oceanographer and expert on the Southern Ocean at the Australian government’s Commonwealth Scientific and Industrial Research Organisation (CSIRO).

“It’s something that is a concern because it touches on so many aspects of the Earth, including climate, sea level, and marine life.”

The finding comes months after modelling, which Rintoul was involved in, that predicted a 40% slowdown in the circulation by 2050.

“The model projections of rapid change in the deep ocean circulation in response to melting of Antarctic ice might, if anything, have been conservative,” Rintoul said. “We’re seeing changes have already happened in the ocean that were not projected to happen until a few decades from now.”

The overturning circulation originates in the cold and dense waters that plunge down deep off Antarctica’s continental shelf and spread to ocean basins globally. It brings oxygen to the deep ocean and returns nutrients to the surface ocean. “What’s driven the slowing is the fact that that dense shelf water is not as dense as it used to be because it’s not as salty as it used to be,” Rintoul said.

The melting of Antarctic glacial ice, the researchers found, has resulted in additional freshwater, increasing buoyancy.

The study looked specifically at changes in overturning circulation in the Australian Antarctic basin, but the researchers believe a “circumpolar slowdown” is occurring.

“The Australian Antarctic basin is the best ventilated of all the deep basins in the sense that it gets more … oxygen-rich water getting to the the bottom,” Rintoul said. “The signal in that basin might provide a kind of early warning of changes that might happen around Antarctica.”

Etc.