Cited research: Proc. R. Soc. B doi:10.1098/rspb.2010.0863 (2010)

Sperm whales in the Southern Ocean are helping to reduce atmospheric carbon dioxide levels, rather than adding to them as marine mammals have been assumed to do.

Trish Lavery at Flinders University in Adelaide, Australia, and her co-workers calculated that the 12,000 or so sperm whales (pictured) inhabiting the Southern Ocean facilitate the removal of 240,000 tonnes more carbon from the atmosphere per year than they add through respiration. The whales' iron-rich faeces fertilize iron-starved waters and stimulate the growth of phytoplankton. As these microscopic marine organisms sink to the ocean floor, it is thought that they take with them 20–40% of the carbon they have fixed through photosynthesis.

Credit: H. MINAKUCHI/MINDEN PICTURES/FLPA

The authors say that other whale species may be having the same effect and warn that the hunting of sperm and other whales has probably decreased the removal of carbon from the atmosphere. N.G.