A now-defunct California company back in 2007 attempted to fertilize the ocean off the coast of Ecuador with iron to prod plankton to grow. Such a bloom, it proclaimed, would suck up carbon dioxide (CO₂) and then send it to the ocean floor as the one-celled plants died and sank. The company, Planktos, sank last year before that could ever happen. But new research suggests that its CEO Russ George and his ilk may have been on to something: plankton blooms do eliminate more CO₂ than regular growth.

Raymond Pollard of the U.K.'s National Oceanography Center in Southampton and his colleagues observed the natural plankton blooms near the Crozet Islands some 1,400 miles (2,200 kilometers) southeast of South Africa, near Antarctica. The waters to the north of the islands are enriched with iron from their volcanic rocks and, each spring, a more than 46,000 square mile (120,000 square kilometer) bloom blossoms.

By dragging a sensor through the surface and deep water, researchers measured increases in the organic carbon matter (dead plankton) at depths of 328 feet (100 meters) and 9,842 feet (3,000 meters) as much as three times as high as in areas to the south of the islands with much smaller, unfertilized blooms. That means as much as three times more of the CO₂ was being absorbed and sent to the bottom of the ocean—some 25 millimoles of organic carbon versus the typical seven millimoles.

That said, even plankton entombing 25 millimoles of carbon and sending it to the watery depths is much smaller than previous estimates, such as those from Planktos—just 5 percent of the CO₂ being absorbed at the surface. "It still falls 15 to 50 times short of some geo-engineering estimates," Pollard writes in Nature.

And, of all the possible geoengineering schemes—from launching mirrors into space to planting trees—it delivers the smallest bang for the buck even at those high estimates, according to a new analysis from earth scientist Tim Lenton of the University of East Anglia in England. Further, countries that have signed the London Convention governing international behavior in the open sea dismissed ocean fertilization because of its minimal impact on climate change and potential side effects.

Neverthelesss, the Germans, for one, are attempting it right now. The Polarstern in Antarctic waters will soon begin dumping 20 tons of iron sulfate into an area of 116 square miles (300 square kilometers) with an eddy current and studying the results for some 40 days, as part of an experiment for the Alfred Wegener Institute.

Credit: © R. T. Pollard