Antarctic ocean currents heading for collapse- report

Rapidly melting Antarctic ice is causing a dramatic slowdown in deep ocean currents and could have a disastrous effect on the climate, a new report warns.

The deep-water flows which drive ocean currents could decline by 40% by 2050, a team of Australian scientists says.

The currents carry vital heat, oxygen, carbon and nutrients around the globe.

Previous research suggests a slowdown in the North Atlantic current could cause Europe to become colder.

The study, published in the journal Nature, also warns the slowdown could reduce ocean's ability to absorb carbon dioxide from the atmosphere.

The report outlines how the Earth's network of deep ocean currents are driven by the downwards movement of cold, dense saltwater towards the sea bed near Antarctica.

But as fresh water from the ice cap melts, sea water becomes less salty and dense, and the downwards movement slows.

This deep ocean current, or "overturning", has been relatively stable for thousands of years, scientists say, but it is now being disrupted by the warming climate.

"Our modelling shows that if global carbon emissions continue at the current rate, then the Antarctic overturning will slow by more than 40 per cent in the next 30 years - and on a trajectory that looks headed towards collapse," study lead Professor Matthew England said.

"If the oceans had lungs, this would be one of them," Prof England, an oceanographer at Sydney's University of New South Wales, told a news briefing.

Scientists spent 35 million computing hours over two years to produce their models, which suggest deepwater circulation in the Antarctic could slow at twice the rate of decline in the North Atlantic.

It suggested changes to the conveyor-belt-like Atlantic Meridional Overturning Circulation (Amoc) could cool the ocean and north-west Europe, and affect deep-sea ecosystems.

The latest study's findings also suggest a slowdown in circulation would also mean the ocean could not be able to absorb as much carbon dioxide from the atmosphere as its upper layers became "stratified".

Waters below 4,000 metres (13,123 ft) would stagnate, Prof England warned, and prevent vital ocean nutrients reaching marine life.

"[It's] stunning to see that happen so quickly," said climatologist Alan Mix from Oregon State University, a co-author of the latest Intergovernmental Panel on Climate Change (IPCC) assessment.

"It appears to be kicking into gear right now. That's headline news," he told Reuters.

The effect of Antarctic meltwater on ocean currents has not yet been factored in to IPCC models on climate change, but it is going to be "considerable", Prof England said.

The study also highlighted how warming oceans could trigger greater melting of the western Antarctica ice shelf, but it did not examine how this could create a feedback effect, and even more melting.