Coastal oceanographers have discovered a new source of CO₂ (carbon dioxide) that is likely to alter climate change models used to predict rates of global warming.

An international consortium of scientists, led by Australian Institute of Marine Science (AIMS) researcher Dr Gregg Brunskill, has disproved the long-held belief that continental shelves in wet tropical areas around the world act as significant carbon sponges, removing carbon dioxide out of the atmosphere by burying organic matter in sediment.

Contrary to most current climate change models, the latest evidence shows continental shelves to be a source of carbon to the atmosphere. It is an important finding because of the implications for the global carbon budget, and will inform future strategies dealing with global warming.

Dr Brunskill, a biogeochemist, said it may force those predicting the fate of fossil fuel carbon dioxide and climate change to rework their models.

"After years of speculation by modelling, we are now a step closer to getting a better grip on how much carbon the earth’s oceans suck out of the atmosphere, acting as carbon sinks or sources of carbon."

The latest research is the result of an international project called TROPICS – Tropical River-Ocean Processes in Coastal Settings – that set out to identify the role continental shelves play in the carbon cycle.

Dr Brunskill and his AIMS colleagues, Irena Zagorskis and John Pfitzner, studied the burial rate of organic carbon in the rapidly accumulating sediment of the Gulf of Papua. Other study sites included the Great Barrier Reef, the North West Shelf off WA, and the coastal zone of the Amazon River in South America. "The Gulf of Papua is considered to be representative of the wet tropics because everything happens very quickly and on a large scale in this region," Dr Brunskill said.

"Our measurements suggest that most of the organic carbon being delivered to the continental shelf of the Gulf of Papua by rivers and by estuarine productivity is being oxidised and returned to the atmosphere as the greenhouse gas, carbon dioxide," he said.

More than 20 international research institutions in Australia, Indonesia, PNG, and the United States are involved in the project, which has reached its final phase.