How Whale Feces Slows Down Ocean Warming

LONDON — There is plenty yet to learn about the causes and effects of climate change, and here is one fact you may perhaps not have known until now: defecating sperm whales are helping to slow the warming of the Southern Ocean.

A team of Australian scientists and colleagues based at Flinders University in Adelaide reported in Proceedings of the Royal Society B (in 2010) that the whales help to increase levels of iron in Antarctic waters (which are iron-deficient).

Iron is important for marine life, and the polar oceans are important for helping to regulate atmospheric CO2 levels. So the whales' personal hygiene is helping vastly smaller lifeforms to thrive, which in turn keeps the ocean ecosystem in balance and able to recycle carbon safely to the seabed.

Scientists had believed that the whales' breathing decreased the efficiency of the Southern Ocean's biological pump by returning carbon from the depths to the surface and thence to the atmosphere, where it would add to the greenhouse gases already there.

But the Flinders team says that by consuming prey in deep water (the whales search for squid  at 1,200 meters or even further down) and then releasing iron-rich liquid feces into the sunlit zone near the surface, the whales instead stimulate new primary production and return the carbon to deep water.

Damaged by whaling

"Primary production" is the scientific term used to describe the minute forms of life produced by the effect of light in the presence of nutrients and - crucially - iron.

The researchers say Southern Ocean sperm whales stimulate the return of 40,000 tons of carbon annually to the deep ocean but breathe out only half that amount. So by stimulating new primary production, the 12,000 Antarctic whales act as a carbon sink, removing twice as much carbon from the atmosphere as they add by their breathing.

The team adds that the ability of the Southern Ocean to act as a carbon sink has been diminished by the large-scale killing of sperm whales during the era of industrial whaling, which reduced the global populations of many whale species to a fraction of their historic levels.

The researchers say the killing of the whales, by decreasing iron inputs to the surface zone, has had a serious impact. "This nutrient loss has undoubtedly altered the dynamics and food-web structure of these environments and this has decreased carbon export to the deep ocean", they conclude.

Not unique

News of the researchers' conclusions, which have so far gone largely unreported, was given to journalists covering a recent meeting in Hong Kong of the Global Ocean Commission by Professor Alex Rogers, of the Department of Zoology at the University of Oxford, UK.

Asked by the Climate News Network whether the findings might apply to other whale species in other oceans, he said: "Not for iron, as the Southern Ocean is a high-nutrient low-chlorophyll area and thus primary production in this region is specifically limited by iron. In most other parts of the ocean it is limited by nitrates."

But a similar paper had shown that before industrial whaling began whales had been the primary source of nitrates through the same process in Chesapeake Bay, on the US Atlantic coast. So fertilization through defecation was likely to be a common mechanism, although different constituents of the feces were important, and in the Antarctic krill might also be important in iron release.

Professor Rogers said whales made other useful contributions to human welfare. Taken together, the toothed whales — a group including sperm whales, belugas and narwhals — were thought to contribute 0.5-1.0% of all the energy needed  for ocean mixing.