"Our climate simulations predict a decrease in oxygen at depths of 500 to 2500 metres in the Southern Ocean and from two research expeditions we now have observed changes in oxygen that support these predictions," says CSIRO's Dr Richard Matear.

"The interpretation is that less oxygen-rich water is penetrating into the ocean and this in turn gives additional credibility to climate change models. The oxygen analysis provides a new benchmark of understanding for researchers."

The Southern Ocean is considered by oceanographers as the 'lungs' of the world's oceans. Fifty-five per cent of the water that regenerates the deep ocean is formed in this region and hence it is an important region to monitor for changes.

Dr Matear said that while no investigation had yet been made on impacts of these changes on marine life, further Southern Ocean sampling was conducted in late 2001 from the Antarctic supply ship Aurora Australis to confirm trends showing up in the climate simulations.

Scientific observations of ocean conditions are based on sampling temperature, salinity, oxygen and nutrients in the ocean from research vessels.

Funded through the Australian Greenhouse Offices's Climate Change Research Program, Dr Matear, Dr Tony Hirst, also of CSIRO and Dr Ben McNeil from the Antarctic Cooperative Research Centre used chemical data gathered during oceanographic research voyages south of Australia to look for changes in the ocean conditions.

The first was on the ship Eltanin in 1968. The second was a World Ocean Circulation Experiment voyage in 1995. Data from the two cruises were compared in the polar and sub-polar regions.

"Climate models predict that increasing greenhouse gases in the atmosphere will change our climate. However, the range of observations available to assess these model predictions is limited," says Dr Matear.

"Next to temperature and salinity, oxygen is the most measured quantity in the ocean and through these models, we have been able to demonstrate that oxygen is sensitive to climate change projections."

"Having demonstrated that oxygen is a valuable indicator of climate change in our models, we now have a quantity to monitor to detect future changes," he says.

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