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Save the whale, and it’ll save you too, say Australian scientists, by recycling iron in the ocean through its poo.
Iron is a major growth factor for algae, which absorb CO2 and thus counteract global warming.
When algae die, they sink to the bottom, taking the precious iron with them. But when they’re eaten by krill, which then become prey for larger animals such as whales, the iron stays in the food chain.
Australian Antarctic Division scientist Dr Steve Nicol looked at tissue samples from four species of baleen whales and seven species of krill. The team also examined faecal samples from the whales – which must have been fun.
“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,” he said.
“Approximately 24 percent of the total iron in the Southern Ocean surface water is currently stored within krill body tissue.”
The most recent estimates of krill biomass in the Southern Ocean is 379 million tonnes, storing about 15,000 tonnes of iron.
“When whales consume the iron-rich krill, they excrete most of the iron back into the water, therefore fertilising the ocean and starting the whole food cycle again,” Dr Nicol said.
“The baleen whales’ faecal iron concentration is calculated to be about 10 million times that of Antarctic seawater,” he said.
Before commercial whaling began early last century whales used to consume about 190 million tonnes of krill, converting this into about 7,600 tonnes of iron-rich faeces.
“This monumental fertilising effort means the whales may have been responsible for recycling about 12 percent of the current iron content in the surface layer of the Southern Ocean,” Dr Nicol said.
The research suggests that increasing the numbers of baleen whales could improve the ocean’s ability to absorb CO2 – making swimming in slurry well worth it.