CC-licensed: Marc Veraart

New research from a pair of scientists at the excellently-named Flinders University in Australia reveals that sperm whales are actually able to offset their own carbon emissions. Like all mammals, sperm whales take in oxygen and turn it into carbon dioxide, but it turns out that the creatures also defecate iron-rich nutrients which stimulate phytoplankton growth.

That extra phytoplankton, which wouldn't otherwise exist due to the natural lack of iron in the Southern Ocean, takes carbon dioxide out of the atmosphere and replaces it with oxygen during photosynthesis. The carbon sinks to the bottom of the ocean when the phytoplankton dies, removing it from the atmosphere for millennia and eventually -- under the right conditions -- becoming oil.

Trish Lavery and Jim Mitchell reckon that the whale population in the Southern Ocean, which numbers around 12,000, defecates around 50 tonnes of iron per year into the photic zone - the zone in the upper regions of the ocean where there's enough light for photosynthesis to occur. That stimulates enough growth of phytoplankton for around 1.3 million tonnes of carbon to be taken out of the atmosphere, of which 20-40% sinks into the deep ocean -- about 400,000 tonnes. The rest cycles back through the food chain.

Conversely, the whales only breathe out around 200,000 tonnes of carbon into the atmosphere each year, resulting in a net reduction of 200,000 tonnes overall. There's also a positive feedback loop in that whales concentrate together in groups, defecating greater amounts of nutrient into a smaller area, and increasing the growth of phytoplankton further. 

Of course, commercial whaling will decrease the numbers of these whales, and as a direct result, the ability of these whales to offset humanity's carbon emissions will be reduced. At the time of writing, the International Whaling Commission has imposed a ban on commercial whaling, but it's due to be reconsidered in a meeting in Agadir, Morocco on 21 June, 2010. For more information on that, visit the Whale and Dolphin Conservation Society's website.


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