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UNIVERSITY OF NEW SOUTH WALES
The deep-sea circulation forming around Antarctica could be headed for collapse, scientists say.
Such a decline in this ocean circulation will stall the bottom of the oceans and have further impacts on climate and marine ecosystems for centuries to come.
The findings are detailed in a new study coordinated by Scientia Professor Matthew England, associate director of the ARC Center for Excellence in Antarctic Science (ACEAS) at UNSW Sydney. The work, published today in Nature, includes lead author Dr. Qian Li – formerly from UNSW and now at Massachusetts Institute of Technology (MIT) – and co-authors from the Australian National University (ANU) and CSIRO.
Cold water that sinks near Antarctica drives the deepest current of the overturning circulation – a network of currents that spans the world’s oceans. The overturn carries heat, carbon, oxygen, and nutrients around the globe. This affects the climate, sea levels and the productivity of marine ecosystems.
“Our modeling shows that if global carbon emissions remain at current levels – and on a course heading towards collapse, Antarctica’s overturning will slow by more than 40 percent over the next 30 years,” says Prof. England .
modeling of the deep sea
About 250 trillion tons of cold, salty, and oxygen-rich water sink near Antarctica every year. This water then spreads north, carrying oxygen to the depths of the Indian, Pacific, and Atlantic oceans.
“If the oceans had lungs, this would be one of them,” says Prof. England.
The international team of scientists modeled the amount of Antarctic deep water that will be produced under the IPCC’s “High Emission Scenario” by 2050.
The model captures details of ocean processes that previous models could not, including how predictions for meltwater from ice might affect circulation.
This deep-sea current has remained in a relatively stable state for thousands of years, but as greenhouse gas emissions increase, Antarctic overturning is expected to slow significantly over the next few decades.
Effects of reduced Antarctic overturning
If this deep-sea current collapsed, the oceans below 4000 meters would stagnate.
“This would lock nutrients in the deep sea and reduce the nutrients available to support marine life near the sea surface,” says Prof England.
co-author dr. Steve Rintoul of CSIRO and the Australian Antarctic Program Partnership says the model simulations show a slowdown in overturning, which then leads to rapid warming of the deep sea.
“Direct measurements confirm that the warming of the deep sea is actually already underway,” says Dr. Rintoul.
The study found that melting ice around Antarctica makes nearby ocean water less dense, which slows Antarctica’s overturning circulation. The melting of the Antarctic and Greenland ice sheets is expected to further accelerate as the planet warms.
“Our study shows that the melting of the ice sheets has dramatic effects on the overturning circulation that regulates the Earth’s climate,” says Dr. Adele Morrison, also from ACEAS and the ANU Research School of Earth Sciences.
“We are talking about the possible long-term extinction of an iconic body of water,” says Prof. England.
“Such profound changes in the way ocean heat, freshwater, oxygen, carbon and nutrients are transformed will significantly affect the oceans for centuries to come.”
METHOD OF RESEARCH
Slowing and warming of the abyssal ocean driven by Antarctic meltwater
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