ANTARCTIC CLIMATE & ECOSYSTEMS COOPERATIVE RESEARCH CENTRE
Media Release
embargoed until 10:00 am 17 April 2008
Polar Year expedition returns with evidence of ocean change
The Aurora Australis returns to Hobart this morning, after completing a major oceanographic expedition across the Southern Ocean.
The Climate of Antarctica and the Southern Ocean (CASO) voyage obtained the most accurate and complete measurements of the ocean currents between Australia and Antarctica yet taken, providing important information that will improve models used to predict climate change.
“We have collected a remarkable data set of observations from the Southern Ocean, covering a wide range of physical, chemical and biological variables says voyage chief scientist Dr Steve Rintoul, a Program Leader at the Antarctic Climate & Ecosystems Cooperative Research Centre (ACE CRC).
The voyage was part of an International Polar Year (IPY) experiment involving 20 ships and scientists from 18 nations, supported by the ACE CRC, CSIRO]s Wealth from Oceans National Research Flagship, the Australian Antarctic Division, and the National Science Foundation of the USA.
The basic question motivating our collective effort is whether the Southern Ocean is changing, and if so, what are the consequences for climate and biological productivity? According to Dr Rintoul.
The IPY has given us an opportunity to harness resources of oceanographic institutions around the world to obtain a snapshot of the Southern Ocean with unprecedented detail.
By combining all of the observations from the many nations involved in CASO, we will be able determine how the Southern Ocean may influence climate, now and in the future, he says.
Dr Rintoul says that the Southern Ocean is the only place on Earth where water is exchanged among all the major oceans. The largest current in the world ocean circles Antarctica and has been referred to as the flywheel of global ocean circulation. By connecting the ocean basins, this current influences climate and ocean circulation patterns over much of the globe.
The Southern Ocean also is one of the few places in the world where conditions are right to make surface water sink into the deep ocean, a key link in the global system of ocean currents that control climate.
Our preliminary results from the voyage suggest the dense water sinking near Antarctica is continuing to become less salty and less dense.
The changes are quite large for the deep ocean, where conditions are usually very stable, says Dr Rintoul.
The Southern Ocean also acts to slow the rate of climate change by absorbing large amounts of carbon dioxide from the atmosphere.
Recent studies suggest the Southern Ocean may be becoming less efficient at soaking up carbon dioxide. Our measurements of how much carbon dioxide is accumulating in the ocean will provide a critical test of this idea.
According to Dr Rintoul, The next challenge is to sort out exactly what the changes in the ocean tell us about how the climate near Antarctica is changing.
One hypothesis is that warmer ocean temperatures are causing faster melt of glacial ice at the edges of the Antarctic continent. In the coming months, measurements of oxygen isotopes will be used to test this hypothesis, while measurements of chlorofluorocarbons (CFCs) will be used to map the flow of the dense water away from Antarctica and to assess whether the rate at which this dense water sinks is changing with time.
Another major achievement of the voyage has been the first measurements of the concentration of iron and other metals throughout the full water depth between Australia and Antarctica.
Growth of phytoplankton, the base of the entire Southern Ocean food chain, depends on the amount of iron dissolved in sea water, says Andy Bowie of the ACE CRC, but the sources and distribution of iron in the ocean are poorly understood because it is very difficult to measure iron from a steel ship without contaminating the samples.
To overcome the problem, new, ultra-clean techniques were used to provide high quality measurements of iron and other metals present at very low concentrations.
Also on the voyage, novel moorings that use sound to measure ocean currents were deployed to make the first accurate observations of how much dense water sinks near Antarctica during winter, when ship visits are rare. The moorings will be recovered next summer.
Antarctic CRC Program Leader and CSIRO Fellow Dr Rintoul was the Voyage Leader and Chief Scientist on the Aurora Australis, and he co-chairs the international CASO program.
Dr Rintoul will be available for interview.
Interviews dockside at:
Date: 17 April 2008
Time: 10:00 am
Location: Macquarie 4 (M4) wharf
Clearance: Security clearance is required for port safety reasons. A media pass, port security or driver's licence/photo id required. A short port safety induction will be required for all media not previously inducted. Please contact Jess Tyler on 0419 315 381 if you are on the wharf and experiencing difficulty with access.
For more information:
Jess Tyler, Communications Manager
Antarctic Climate & Ecosystems Cooperative Research Centre
Tel: +61 3 6226 2265 • M: 0419 315 381 E:
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