March 29 () –
The deep ocean circulation that forms around Antarctica may be about to collapsewarns a new study published in Nature.
Such a decrease in this ocean circulation it will stagnate the bottom of the oceans and generate more impacts that will affect the climate and marine ecosystems for centuries to come.
Cold water sinking near Antarctica drives the deeper flow of the overturning circulation, a network of currents that spans the world’s oceans. Tipping carries heat, carbon, oxygen and nutrients around the globe. This influences the climate, sea level and the productivity of marine ecosystems.
“Our model shows that if global carbon emissions continue at the current rate, then Antarctic tipping will be reduced by more than 40 percent over the next 30 years, and on a trajectory that seems headed for collapsesays Professor Matthew England, Deputy Director of the ARC Center for Excellence in Antarctic Science (ACEAS) at UNSW Sydney.
About 250 trillion tons of cold, salty, oxygen-rich water sinks near Antarctica every year. This water then spreads north and carries oxygen to the depths of the Indian, Pacific, and Atlantic oceans.
“If the oceans had lungs, this would be one of them.says Professor England. The international team of scientists modeled the amount of Antarctic deep water produced under the IPCC ‘high emissions scenario’ up to 2050.
The model captures details of ocean processes that previous models have not been able to, including how predictions of ice meltwater might influence circulation.
This deep ocean current has remained in a relatively stable state for thousands of years, but with increasing greenhouse gas emissions, Antarctic tipping is projected to slow significantly in the coming decades.
With a collapse of this deep ocean current, the oceans below 4,000 meters would stagnate. “This would trap nutrients deep in the ocean, reducing the nutrients available to support marine life near the ocean surface,” says Professor England.
Co-author Dr Steve Rintoul of CSIRO and the Australian Antarctic Program Association says model simulations show a slowdown in capsizing, which then leads to rapid warming of the deep ocean.
“Direct measurements confirm that deep-ocean warming is already underway,” says Dr. Rintoul. The study found that melting ice around Antarctica makes nearby ocean waters less dense, which slows the Antarctic overturning circulation. Melting of the Antarctic and Greenland ice sheets is expected to continue to accelerate as the planet warms.
“Our study shows that melting ice sheets have a dramatic impact on the circulation that regulates Earth’s climate.says Dr Adele Morrison, also from ACEAS and the ANU Research School of Earth Sciences.
“We’re talking about the possible long-term extinction of an iconic body of water.says Professor England. “Such profound changes in ocean heat, fresh water, oxygen, carbon and nutrients will have significant adverse impacts on the oceans for centuries to come.”
