Last February, Matthew Charette and other scientists chugged through the icy, roiling waters of the Southern Ocean near Antarctica to conduct a very simple experiment.
“Basically we dumped a whole bunch of iron in the ocean and then waited to see what happened,” says Charette, an oceanographer at the Woods Hole Oceanographic Institute in Massachusetts.
The international team of scientists actually mixed just over 9 ½ tons of iron sulfate with water and then hosed the mixture into a 5-mile-wide stretch of ocean over the course of four days.
The experiment was the latest of three variations of its kind since 1993, when the late oceanographer John Martin declared, “Give me a half-tanker of iron, and I’ll give you an ice age.”
While Charette and his colleagues were hoping to learn more about what may have triggered ice ages of the past, some believe a large-scale dumping of iron in the ocean could curb the apparent warming of the world’s climate in the future.
What does iron have to do with a cooling planet? The answer begins with tiny, waterborne plants known as plankton.
A Pollution Sponge
Martin learned that ocean plankton are commonly iron-deprived, so by adding iron to the ocean, these tiny plants can flourish.
Sure enough, all three iron-nourishing experiments — even the most recent one in the normally barren Southern Ocean, that part of the Indian Ocean south of Australia — yielded booming populations of plankton. Like trees and plants on land, plankton plays a big role in soaking up carbon dioxide. And carbon dioxide, belched by factories and vehicles, is one of the main “greenhouse” gases that many fear is contributing to global warming by trapping heat inside the Earth’s atmosphere.
By adding iron, Martin suggested, you add plankton that absorb carbon dioxide. Tug the absorbed gas to the bottom of the sea as the plankton die and sink — and that cools the Earth.
But while adding iron to oceans is simple, Charette and other scientists warn the results may be endlessly complex.
Sallie Chisolm, an environmental engineer and biologist at the Massachusetts Institute of Technology, says the iron nourishment theory is “seductive in its simplicity.” She argues the complex ecosystems of oceans make it impossible to predict reactions to a large-scale introduction of iron.
One possible result, for example, is the proliferation of an unwanted species like jellyfish that might feed on a growing breed of plankton. Or, she adds, iron nourishment could prompt microscopic animals to flourish and they could, in turn, suck out vast supplies of oxygen from the ocean.
“We’re just starting to understand how the ecosystem responds to this change,” she says. “The whole food web is affected by it and there’s a lot more to learn.”
The Swirl That Lingered
Chisolm points out that even the relatively small-scale experiment in the Southern Ocean had puzzling results. A month after the team had left the Southern Ocean, images snapped by satellites revealed the plankton had expanded to a nearly 100-mile-long green ribbon of plankton that persisted even in the choppy ocean waters.
“We never expected it to last as long as it did,” says Charette.
Since the plankton stuck around, the team was unable to measure any movement of carbon — in the form of dying plankton — to the bottom of the ocean. Charette points out that unless plankton sinks to the bottom, carbon-dioxide levels won’t drop, since tiny animals will feed on the plankton at the surface and then re-release carbon dioxide.
The team suspects those plankton levels eventually died out and drew carbon levels to the ocean bottom. But that remains uncertain since the scientists were unable to linger in the harsh austral climate long enough to continue tests.
“We know you can dump iron and grow plants in many places,” says Kenneth Buesseler, an oceanographer at the Woods Hole Oceanographic Institute who participated in the Southern Ocean study that appeared in the journal Nature. “But details about the long-term effects are still unknown.”
Bigger Plans Under Way
Still, at least one person is eager to try iron nourishment now. For nearly five years, Mark Markels has championed the idea of pumping vast quantities of iron solutions into waters off the coast of the Marshall Islands in the Pacific Ocean. Last year, Markels nearly secured a license from the Marshall Islands government to fertilize waters off the islands. He had hoped increased plankton levels would nourish growing fish populations. Then his company, Ocean Farming Inc., would charge companies to fish in the nourished waters. But the Marshall Islands’ government eventually denied Markels permission.
Markels has since set his sights on a large-scale experiment off the coast of the Galapagos Islands. This time, he hopes to generate data that might support significant iron-nourishing projects in the future.
“All experiments done so far have been too small,” Markels says. “We’d like to do one that is 5,000 square miles — the size it would need to be in order to have a measurable effect.”
Markels says funding for his massive-scale experiment may come from companies and individuals interested in purchasing so-called gas emission credits. Companies use such credits to offset requirements to reduce their emissions levels of greenhouse gases. But Markels stresses that neutral parties such as universities would perform analysis of the experiment. He also adds that if any adverse effects were to appear, his company would halt the experiment in time to prevent a lasting impact.
“We need a technology that can put to rest people’s concerns about global warming,” Markels says.
Others have also become interested in the idea of using the ocean to absorb unwanted emissions. At least three patents have been issued to individuals exploring ways of nourishing ocean waters to sop up greenhouse gases.
But for Chisolm, the proposed solutions are almost as worrisome as the problem itself.
“I think it’s important to develop some rational policy measures to oversee these kinds of experiments,” she says. “They could introduce changes that we can’t possibly predict.”