Melting Antarctic ice predicted to cause rapid slowdown of deep ocean current by 2050

New research by Australian scientists suggests 40% slowdown in just three decades could alter world’s climate for centuries

Melting ice around Antarctica will cause a rapid slowdown of a major global deep ocean current by 2050 that could alter the world’s climate for centuries and accelerate sea level rise, according to scientists behind new research.

The research suggests if greenhouse gas emissions continue at today’s levels, the current in the deepest parts of the ocean could slow down by 40% in only three decades.

This, the scientists said, could generate a cascade of impacts that could push up sea levels, alter weather patterns and starve marine life of a vital source of nutrients.

A team of Australian scientists looked at the deep ocean current below 4,000 metres that originates in the cold, fresh and dense waters that plunge down off Antarctica’s continental shelf and spread to ocean basins around the globe.

Prof Matt England, of the Climate Change Research Centre at the University of New South Wales and a co-author of the research published in Nature, said the whole deep ocean current was heading for collapse on its current trajectory.

“In the past, these circulations have taken more than 1,000 years or so to change, but this is happening over just a few decades. It’s way faster than we thought these circulations could slow down.

“We are talking about the possible long-term extinction of an iconic water mass.”

The research looked at what would happen in the deep ocean around Antarctica if the fresher water melting from ice sheets was added to climate modelling.

The modelling for the study assumed that global greenhouse gas emissions remained on their current path, but England said lower emissions could lessen the amount of ice melting which – in turn – could slow the decline.

The slowdown in the deep ocean current relates to the amount of water that sinks to the bottom and then flows north.

The study did not attempt to explain or quantify the knock-on effects, but the authors wrote the slowdown would “profoundly alter the ocean overturning of heat, fresh water, oxygen, carbon and nutrients, with impacts felt throughout the global ocean for centuries to come”.

In a briefing, the authors said the deep ocean current influenced the climate around the world, with the potential to radically shift rainfall.

England said the slowdown of the deep ocean current caused those deep waters to heat up.

But as that deep water becomes isolated, it could then cause the upper ocean around the continent to get hotter, kicking off a feedback loop where more melting causes accelerated slowing of the current, which then causes more heating and more ice sheet melt.

The deep water that warms the fastest in the study, England said, was in the same areas – particularly in west Antarctica – where ice sheets were already vulnerable and melting.

“We don’t want to set off a self-reinforcing mechanism in those places,” he said, adding that the slowdown effectively stagnates the deep ocean, starving it of oxygen.

Dr Qian Li, formerly of the University of New South Wales and now at the Massachusetts Institute of Technology, was the lead author of the research, coordinated by England.