Whales may seem an unlikely tool for manipulating the planet's climate, but it turns out they can play a major role in doing exactly that. Or rather, their excrement can. It sounds outlandish, but new research suggests whale feces may be among our best hopes for coaxing Earth's oceans to suck up more carbon.

Filter-feeding baleen whales are like giant vacuum cleaners, slurping down nearly two tons of tiny, shrimp-like krill in the deep ocean every day. When they return to the surface, baleens spew gargantuan plumes of shrimpy excrement (fondly nicknamed "poo-namis") back out.

Getting the ocean to suck up more carbon has been the aim of geoengineering, a field that examines the possibilities of artificially altering the climate to cool it off. One of the best-known so-called geoengineers is non-scientist Russ George, who, in a rogue experiment, dumped iron into the ocean to see if it would spur plankton to bloom. But what if whales could just do this on their own? If we could better protect, and even breed more whales, we might have a safer, so-called geoengineering option right at our fingertips.

Scientists suspect these marine defecations stimulate phytoplankton—the microscopic, plant-like organisms that transfer carbon from the atmosphere to the deep ocean. But actual data on this potential source of ocean fecundity is scarce.

Lavenia Ratnarajah and her colleagues at the University of Tasmania had a hunch that whale poop might be a big deal in one of the most biologically impoverished places on Earth: The vast Southern Ocean that encircles Antarctica. Here, a paucity of trace metals—iron, cobalt, cadmium, zinc and so forth—restricts phytoplankton growth. It's been suggested that the Southern Ocean represents a massively untapped carbon sink; if only we could figure out how to amp up its primary producers.

Ratnarajah analyzed tissue and fecal samples from nearly a dozen different whale species and krill for a host of trace metals. Metal concentrations in krill tissue were up to 4.8 million times greater than Southern Ocean seawater, while whale poop contained up to 10 million times more metals. Among the metals most concentrated in whale feces were iron and cobalt, two of the scarcest nutrients in the Southern Ocean.

So, it seems the krill-whale food chain indeed concentrates trace metals into a life-sustaining elixir of excrement. While other oceans receive a steady stream of these metals from continental runoff and dust, in the remote Southern Ocean, animal defecations may be the critical source. This finding points to a big reason for bringing whales back: They may be the safest option we've got for cajoling the ocean into mopping up some extra carbon.

Image: Phytoplankton, ​Wikimedia

How much additional carbon are we talking? It's tough to say, but researchers have started making some preliminary estimates. In the Southern Ocean, iron defection by the the 12,000-strong population of sperm whales is thought to draw some 200 thousand tons of carbon from the atmosphere every year. As Ratnarajah points out, that's roughly equivalent to 70 thousand vehicles, each traveling 15 thousand kilometers annually.

And that's just one species. With many whale populations hovering at a fraction of their pre-1900s size, it seems we've not only decimated a diverse group of charismatic creatures, but one of the ocean's key biological carbon pumps. (In a related study, scientists calculated that, before commercial whaling took off, sinking whale carcasses probably drew an extra 160 thousand tons of carbon out of the surface ocean every year.)