A light industrial area on the outskirts of Salinas, California, is probably the last place that you would think to look for an oceanographic institute. Yet, that is exactly where I found the Moss Landing Marine Laboratories, the birthplace of one of the decade's most startling scientific experiments.

The experiment, carried out in May and June of 1995, in an open stretch of the Pacific 800 miles west of the Galápagos Islands, involved an attempt to stimulate the growth of plankton by dumping iron into the ocean. During the two weeks of the experiment, the additional plankton that resulted from the fertilization pulled about 2,500 tons of carbon from the water, carbon that eventually would be in large part replenished from the atmosphere.

It was 1987 when oceanographer John Martin at Moss Landing first conceived what has come to be called the "iron hypothesis." Martin, who died in 1993, was a rather extraordinary individual. Working from a wheelchair since a bout with polio, he nonetheless managed on occasion to ship out with his research teams aboard the cramped, overcrowded vessels that are the oceanographer's primary labs. He noted that there are huge areas of ocean (mainly in the waters surrounding Antarctica and in the equatorial Pacific) that have large amounts of nutrients in the form of nitrogen compounds, but very few plankton. These regions also seem to have very low concentrations of iron-on the order of two parts per trillion. Just as lack of a single vitamin or trace mineral can stunt the growth of humans, Martin argued, the dearth of plankton in these otherwise nutrient-rich waters was because of the scarcity of iron.

What interested first Martin and now his successor, Kenneth Coale, are the ocean's phytoplankton — minute floating plants that, like all plants, pull carbon dioxide from their environment and convert it into molecules that they need to live. Think of them as the oceanic equivalent of prairie grass. Stimulating a plankton bloom is the equivalent of fertilizing a prairie. The plants remove carbon dioxide from the atmosphere (directly or indirectly) and store the carbon in their tissues.

Finding ways to remove carbon dioxide from the atmosphere has become a serious business. The surface of the earth is heated by the sun. So-called greenhouse gases — carbon dioxide, methane and water vapor, among others — prevent some of that heat from radiating back out into space. Even without any human activity, the world is about 60 degrees Fahrenheit warmer than it would be without this "greenhouse effect." By the burning of coal and oil — not to mention the burning of tropical rain forests-human beings now add measurable quantities of carbon dioxide to the atmosphere and may be raising the world's temperature.

But draw enough carbon dioxide out of the atmosphere, scientists predict, and that temperature will drop. "Give me a half a tanker of iron," Martin once said, "and I'll give you the next ice age." It wasn't all bluster. Scientists now estimate that iron fertilization could, in principle, remove as much as 20 percent of the human-generated carbon dioxide from the atmosphere at a cost less than alternatives such as large-scale tree planting.

When the first field trial of the idea was conducted in the fall of 1993, shortly following Martin's death, however, things stopped looking so simple. This was what engineers call a "proof of concept" experiment. "The main purpose," says Coale, "was to see whether you could lay down a patch of iron-rich water in the ocean." The iron, in the form of iron sulfate, was fed through two pipes in back of the ship's propellers and dispersed into the ocean. "Being in an agricultural area like the Salinas Valley was a big help," Coale says. "All the equipment for moving around large amounts of fertilizer is available right here."

In a narrow sense, the first experiment was a success. A patch of iron-rich water formed. The concentration of phytoplankton in the patch, however, was only twice that of the surrounding water. In the minds of many, this constituted a serious failure of the whole idea.

There was at least one good reason for this disappointing performance. On the fifth day after the fertilization, less salty and therefore lighter water moved in, burying the patch under a hundred feet of water, away from the light.

I was at the meeting in San Francisco when these results were announced in 1994, and I was really taken aback by the reaction to them. As someone who has, during a checkered career, been involved in a couple of large-scale engineering projects, I wasn't surprised at this type of "failure." In projects like this, the first trial always fails-think of the first American attempts at spaceflight. What surprised me was the reaction of the environmental scientists present. It was almost as if there was a collective sigh of relief, as if the prospect that humanity might find an easy way out of the greenhouse problem was just too much for them to bear. Having heard many of those same scientists advocate the large-scale planting of trees to pull carbon out of the air, I couldn't help wondering why they were so dismayed at the notion of growing phytoplankton instead.

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.

"Wouldn't it be easier to try carpooling first?"

By James Trefil