"The Southern Ocean is considered by oceanographers as the 'lungs' of the world's oceans," the CSIRO said in a statement from Hobart, Tasmania, where about 200 scientists are preparing for a meeting of the Geneva-based World Climate Research Programme's joint scientific committee this week.

The oxygen findings were consistent with climate simulations and with change caused by the build up of greenhouse gases, CSIRO oceanographer Richard Matear told Reuters.

Limited work in the north Pacific also showed declining oxygen content, consistent with model simulations, he said.

CSIRO scientists were now collecting further samples south of Tasmania to widen the sample base. Samples so far had been taken from the sea on a line between Tasmania and Antarctica, with most readings from between 50 and 65 degrees latitude south.

The readings were important for fine-tuning predictions of severe weather events, including floods and rising sea levels, Matear said.

In the much longer term they had importance for the entire life of the seas.

"If you run these models forward for another 3,000-4,000 years you will see significant expansions of regions where there's low oxygen concentration, which will have impacts on marine life," he said.

Next to temperature and salinity, oxygen was the most measured element in the ocean and had now been shown to be sensitive to climate change, he said.

Latest samples were taken in late 2001 from the Antarctic supply ship Aurora Australis, between southern Australia and the Antarctic, to confirm trends showing up in climate simulations.

Results were compared with first samples taken in the 1960s.