Study Challenges Idea of Seeding Oceans With Iron to Curb Global Warming

By Hillary Mayell
for National Geographic News
January 8, 2001

Two researchers may have put the final stake in the heart of the so- called Geritol solution to global warming, a proposal that has intrigued the scientific community for more than a decade.

The idea, which got its name from a tonic touted to treat the effects of iron-poor blood, asserts that seeding the oceans with iron will dramatically increase levels of phytoplankton and therefore draw more carbon dioxide from the atmosphere.

Evidence from ice cores shows that huge blooms of phytoplankton—the microscopic algae that are the basis of the marine food chain—occurred in the waters of the Southern Ocean during peaks in ice ages.

A decade ago, a scientist named John Martin proposed a theory known as the "Iron Hypothesis," which attributed the sudden growth spurts of phytoplankton to an increase in the amount of iron in the sea. Iron acts as a fertilizer for plants.

The theory was borne out by experiments. When scientists seeded small areas of the ocean with iron, big phytoplankton blooms occurred.

But where did the additional iron that fueled the historic pattern of growth spurts in phytoplankton [production] come from? Martin suggested the iron came mainly from wind-swept dust from land that was carried out to sea and deposited into the oceans.

Now, in a study published in the December issue of Paleoceanography, Gabriel Filippelli and Jennifer Latimer challenge that idea. They suggest that the increased amounts of iron were delivered predominantly from deep ocean waters that rose from below—a scenario they call the "Upwelled Iron Hypothesis."

"We looked at Antarctic ice cores and also in ocean cores to test the idea of higher productivity during ice ages," said Filippelli, a paleo-oceanographer and associate director of the Center for Earth and Environmental Sciences at Indiana University–Purdue University, Indianapolis (IUPUI). "We found that yes, phytoplankton productivity is higher, and yes, iron content is higher. But the iron content is far in excess—about ten times higher—than what could be delivered by dust."

The "Geritol Solution"

"Phytoplankton grows on a seasonal basis in the oceans around the world," said Filippelli. "Over longer time scales, we know that ocean plant life was at its most robust in the Southern Ocean during glacial intervals—for example, about 150,000 years ago, and then again 20,000 years ago. The question has been, what caused the increases in productivity?"

Like terrestrial plants, phytoplankton engage in photosynthesis, using sunlight as an energy source to combine water molecules and carbon dioxide and convert them to plant food.

The phytoplankton use carbon dioxide from the atmosphere; therefore, the larger the amount of phytoplankton in the world's oceans, the more carbon dioxide is being drawn from the atmosphere.

Continued on Next Page >>


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