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Tiny ocean plankton can reduce global warming by soaking up unexpectedly large amounts of carbon dioxide but their carbon-bloated cells might damage marine food chains, scientists said on Sunday.

Experiments in a Norwegian fjord showed that plankton - small drifting plants or creatures - could absorb up to 39 percent of the main greenhouse gas, carbon dioxide, in seawater pens that simulate projected climate conditions to 2150.

"This is a massive and surprising change in the carbon content of these organisms," said Ulf Riebesell, a marine biologist at the Leibnitz Institute of Marine Sciences in Kiel, Germany, who led the German and Norwegian experiments.

The results of the study were published in the journal Nature.

Other studies show the oceans have soaked up almost half of the carbon dioxide produced by burning fossil fuels since the late 18th-century start of the Industrial Revolution, but few have examined how greenhouse gases may affect life in the oceans in future.

The positive spin on the study is that plankton's ability to absorb ever more carbon could help the climate by putting a brake on rising temperatures that the UN climate panel says will bring more heatwaves, storms, droughts and floods.

But Riebesell said the study indicated bad news for marine life.

"What appears to be a blessing for the atmospheric greenhouse effect may prove to be a curse for deep ocean ecosystems," the Leibnitz Institute said in a statement.

When plankton die and sink, their decomposition consumes oxygen vital to marine animals living in the depths. "This will enlarge the parts of the oceans that have very little oxygen".