Sperm Whales and Ocean Fertilization

From Not Exactly Rocket Science:

While the world wrangles over ways of reducing carbon emissions, some scientists are considering more radical approaches to mitigating the effects of climate change. Dumping iron dust into the world’s oceans is one such strategy. Theoretically, the iron should act as fertiliser, providing a key nutrient that will spur the growth of photosynthetic plankton. These creatures act as carbon dioxide pumps, removing the problematic gas from the air and storing the carbon within their own tissues. When the plankton die, they sink, trapping their carbon in the abyss for thousands of years.

It may seem like a fanciful idea, but as with much of our technology, nature beat us to it long ago. Trish Lavery from Flinders University has found that sperm whales fertilise the Southern Ocean in exactly this way, using their own faeces. Their dung is loaded with iron and it stimulates the growth of plankton just as well as iron dust does.

Sperm whales are prodigious divers, descending to great depths in search of prey like squid. When they’re deeply submerged, they shut down all their non-essential bodily functions. Excretion is one of these and the whales only ever defecate when they reach the surface. By happy coincidence, that’s where photosynthetic plankton (phytoplankton) make their home – in the shallow column of water where sunlight still penetrates. So by eating iron-rich prey at great depths and expelling the remains in the shallows, the whales act as giant farmers, unwittingly seeding the surface waters with fertiliser.