Need another reason not to kill off the world’s whale populations? Their poop helps the oceans absorb the greenhouse gas carbon dioxide out of the atmosphere.

Researchers with the Australian Antarctic Division and the Antarctic Climate and Ecosystems Cooperative Research Centre (ACE CRC) have found that whale feces is packed with iron. When that iron-rich excrement enters the ocean, it provides food for algae, which absorb carbon dioxide and — after they die and sink to the ocean floor — help safely sequester that carbon away.

In fact, before commercial whaling began wiping out the giant marine mammals last century, whales annually produced some 7,600 tonnes of algae-fueling feces.

“This monumental fertilising effort means the whales may have been responsible for recycling about 12 per cent of the current iron content in the surface layer of the Southern Ocean,” said Steve Nicol, a scientist with the Australian Antarctic Division.

The iron cycle actually begins with tiny krill, which hold significant quantities of iron in their bodies.

“We found that krill concentrated the iron they consumed in their bodies and because they swim near the surface, they keep the iron in the top layer of the ocean,” Nicol said. “Approximately 24 per cent of the total iron in the Southern Ocean surface water is currently stored within krill body tissue.”

With an estimated 379 million tonnes of krill in the Southern Ocean alone, that amounts to an iron supply of about 15,000 tonnes.

Those krill provide a food source for larger creatures like seals, penguins and whales. After whales scoop up large quantities of iron-rich krill, they excrete the undigested bits in even more iron-rich form.

“The baleen whales’ fecal iron concentration is calculated to be about 10 million times that of Antarctic seawater,” Nicol said.

The research suggests that allowing populations of both krill and whales to increase could not only benefit productivity of the Southern Ocean’s ecosystem but could boost the ocean’s ability to absorb carbon dioxide.

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