A vast network of under-sea volcanoes pumping out nutrient-rich water in the Southern Ocean plays a key role in soaking up large amounts of carbon dioxide, acting as a brake on climate change, scientists say.

A group of Australian and French scientists have shown for the first time that the volcanoes are a major source of iron that single-celled plants called phytoplankton need to bloom and in the process soak up CO2, the main greenhouse gas.