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.