France and Australia resume Southern Ocean carbon dioxide research

French and Australian scientists resume measurements of Antarctic waters south of Australia this week to assess their capacity as a massive oceanic sponge to absorb greenhouse gases and store them away for hundreds or perhaps thousands of years.

France and Australia have a joint research program taking measurements from the Antarctic supply ship L’Astrolabe during its voyages between Hobart and the French base at Dumont D’Urville. L’Astrolabe, equipped with a full sampling laboratory, sails from Hobart on Tuesday 19 October in the first voyage of the season. Professor Alain Poisson from the University of Paris and Dr Bronte Tilbrook from CSIRO oversee the research.

Later in the year the ice breaker Aurora Australis will head south from Fremantle to make a similar set of measurements and to extend the work to the west of the Astrolabe track. “The Southern Ocean is so important for controlling the concentration of carbon dioxide in the atmosphere,” Dr Tilbrook says. “The Astrolabe work is helping us obtain a much clearer picture of the interaction between ecosystems and mixing that drives the carbon dioxide exchange between the ocean and atmosphere.”

Dr Tilbrook was a co-author on new research published earlier this year in the journal Science examining the role of the world’s oceans in the global carbon cycle. “The results show the oceans contain about 48 per cent of fossil fuel emissions and more than half of the storage occurs in the Southern Hemisphere,” Dr Tilbrook says. “Before now we had to rely on models to understand ocean carbon storage. Now we have values based on carbon measurements. “This is a big step forward in understanding how the earth system has responded to increases in atmospheric carbon dioxide and is helping to work out what might happen in future.”

Prof Alain Poisson, from the University of Paris, has been working in the Southern Ocean alongside CSIRO scientists for the past 10 years. “We have to know the evolution of the oceans and atmosphere,” he says. “This area is crucial because if something happens here it will react on the global climate.” The 65-metre L’Astrolabe, has become a key platform in this international project. Safely stowed below deck on the former oil-rig tender, Australian and French scientists work in a converted container measure gases above and below the ocean surface.

With only limited shipping entering the Southern Ocean results from the joint monitoring program are being watched closely by climate scientists. Just two years old, the joint French and Australian research project involves constant sampling of the Southern Ocean along the 1000km route south. Dr Tilbrook said the results show that the region around Australia has a fairly significant impact on the ocean capacity for uptake and storage.

“Most of the Southern Hemisphere storage occurs in the sub-Antarctic region, which includes the waters along Australia’s southern shores,” he says. “Deep water with low anthropogenic carbon concentrations upwells off Antarctica and the ocean circulation carries the water north. The surface waters absorb anthropogenic carbon dioxide as they move north. In the sub-Antarctic region the waters become dense enough to sink below the surface and carry the anthropogenic carbon dioxide away from contact with the atmosphere. “The circulation pattern is like a giant conveyor belt and helps drive the ocean capacity to take up carbon dioxide.”

A new series of internationally coordinated research expeditions which includes the Astrolabe and Aurora Australis work are planned through the major oceans to identify how the storage is changing with time.

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