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Phenomena, Comment and Notes

Experiments at sea show we can cause phytoplankton to bloom in areas where it otherwise would not. This could remove carbon dioxide from the atmosphere and slow global warming

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Coale and the study's other principal investigator, Ken Johnson, began the second-round experiment in May of 1995. The first surprise in that experiment came when they dropped the buoy overboard to mark their patch. "It took off at a knot and a half [about two miles per hour]," says Coale, who laughs about it now. "The whole patch was careening across the South Pacific, and we had to follow it. What a ride!" By the end, they had chased that particular patch over 950 miles.

The second surprise came when they started dumping the iron. Instead of putting it all in at once, they made three injections, spaced a few days apart. When they started, the water was a clear, electric blue-the sort of water that makes great photographs for travel posters but has almost no microscopic life in it. Their patch stayed on the surface this time, and in a few days the sea turned green for miles around as the phytoplankton took up the iron and multiplied. "It was like sailing into a duck pond," says Coale.

All sorts of strange things happened in the patch. For example, the scientists were trailing long, sock-like nets in the water to pull up samples that would allow them to estimate the growth of plankton. As soon as the phytoplankton started to bloom, the inside of the nets gummed up with green scum. When scientists tried to raise them, the water wouldn't run out and the nets burst. "When things like that happen," Coale points out, "you don't need statistics to tell you the experiment is a success."

In the end, the phytoplankton mass increased thirtyfold, even more than predicted. Zooplankton counts went up, too, but only to twice the original number. "The grass just got ahead of the cows," is the way Coale characterized his observations.

As a feasibility study, it's clear that the second experiment was a success. It also provided pretty convincing evidence for the iron hypothesis. At least one question remains, however: After phytoplankton bloom, what happens to the carbon when the plankton die?

"We didn't make any measurements, so I can't give you a firm answer to that," says Coale. "I can say, though, that the phytoplankton we saw were diatoms in long chains, which have a pretty high sinking velocity. When we went back into the patch after about two weeks, I saw lots of clumps of phytoplankton in marine snow configurations." ("Marine snow" is the remains of surface-dwelling organisms that clump together and fall constantly to the bottom of the world's oceans. Coale calls the clumps the "dust bunnies of the seas.") At the moment, then, there seems to be a reasonable chance that iron fertilization could pull large amounts of carbon from the atmosphere and store it on the ocean floor.

Some engineers are already talking about how ocean fertilization might be implemented on a larger scale, by systematically releasing iron into the waters surrounding Antarctica. How does someone like Coale, who has devoted his career to studying the oceans, feel about this sort of thing?

"There are a lot of things I'd want to think about before we did anything like that," he says. Pressed for specifics, he points out that as dead plankton sink, they will start to decompose in the upper half-mile of the ocean. In the lower part of this region, there is very little oxygen. If this oxygen is depleted, he argues, the decomposition process might start breaking up the nitrogen compounds and that, in turn, could affect the supply of nutrients on which a lot of the earth's fisheries depend. Obviously, this effect (and others) will have to be investigated before we start any large-scale geoengineering.

"It could well be that we will need iron fertilization as a last-ditch method of averting global warming," Coale says. "People haven't been very responsible about dealing with the problem up to now."

He pauses for a moment, then shakes his head.


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