July 30, 2012
Southern Ocean Mechanism Sequesters Carbon Emissions
Brett Smith for redOrbit.com - Your Universe Online
Using a fleet of robotic floats, a team of British and Australian scientists have uncovered the mechanism in the Southern Ocean that sequesters around 40 percent of the world´s carbon emissions.
A report on the team´s research, which was published this week in Nature Geoscience, showed that “mixed-layer depth, ocean currents, wind and eddies” create plunging currents that draw atmospheric carbon deep into the ocean, where it can remain for hundreds or thousands of years.
"The Southern Ocean is a large window by which the atmosphere connects to the interior of the ocean below,” said lead author Jean-Baptiste SallÃ©e from British Antarctic Survey.
“Until now we didn't know exactly the physical processes of how carbon ends up being stored deep in the ocean. It's the combination of winds, currents and eddies that create these carbon-capturing pathways drawing waters down into the deep ocean from the ocean surface.”
"Now that we have an improved understanding of the mechanisms for carbon draw-down we are better placed to understand the effects of changing climate and future carbon absorption by the ocean,” he added.
Recent studies have also shown that naturally occurring currents in the Southern Ocean can draw carbon dioxide up from deep below the surface.
To study these plunging currents, which can measure 600 miles wide, the researchers launched 80 robotic floats back in 2002 and incrementally expanded the fleet to 3,000 by today. The “Argo” floats are about a meter long and collect detailed temperature, pressure and salinity data. They can dive as deep as 2,000 meters into the ocean for 10 days at a time and are made to perform 150 such trips.
Based on data collected by the smart submersibles, the scientists found that the Southern Ocean absorbs carbon at specific spots where the confluence of factors is just right. Previous theories stated that the ocean absorbed carbon uniformly across its surface.
According to study co-author Steve Rintoul of the Commonwealth Scientific and Industrial Research Organisation (CSIRO), these currents in the Southern Ocean are the most vital oceanic mechanism for eliminating greenhouse gases.
“There are other places in the ocean where the water sinks to the deep ocean, in particular–in the north Atlantic,” he said in an accompanying web video. “But the Southern Ocean is the place with most active exchange between the interior of the ocean away from the surface and the surface layer of the ocean that´s in contact with the atmosphere–including with the carbon dioxide that we are pumping into the atmosphere.”
The scientists noted that the Southern Ocean plays an important role in reducing atmospheric carbon and warned that the factors that contribute to these carbon sequestering currents could be susceptible to climate change, increasing the possibility of a global warming feedback loop.
“If it wasn´t for the ocean acting as a sponge, climate would be changing more rapidly than it is today,” Rintoul said.
"Climate change will definitely interact with this process and modulate it," co-author Richard Matear, of CSIRO, told Reuters.