The financial returns for reducing carbon could be considerable, said Daniel M. Kammen, a professor at the University of California, Berkeley.

In Europe, where there is a market for carbon credits, it is now worth only $2 to offset a ton of carbon emissions. But not long ago, that figure was $35, and it is expected to rise again as the limits imposed under the Kyoto Protocol on global warming start to bite. Planktos believes that it can make a healthy profit if it receives $5 a ton for capturing carbon dioxide.

“The cost of offsetting carbon through these technologies is less than the cost of building solar panels or windmills,” Mr. Kammen said. “There’s no question that this is going to grow,” he said of various carbon offset strategies.

But the question in the case of iron fertilization is whether the exuberance and marketing spirit of Silicon Valley and its can-do attitude are getting ahead of scientific reality. And some oceanographic experts say that there is a risk of doing more harm than good from artificially stimulating plankton growth in the ocean.

It is widely accepted by scientists that dumping iron in certain areas of the ocean can cause plankton to bloom. But there is considerable skepticism over whether doing so will lead to long-term absorption of carbon dioxide from the atmosphere, said Ken Buesseler, senior scientist at the Woods Hole Oceanographic Institution.

Mr. Buesseler said that while carbon might be absorbed initially, there was ample evidence that when the plankton was eaten or decomposed, at least some of the carbon wound up going back into the atmosphere. The level of absorption depends on how much of the resulting mass of plankton sinks to the sea bed.

Image The ship will measure how much carbon dioxide is ingested by the plankton. Critics worry that there may be unintended side effects. Credit... Jay Paul for The New York Times

And some scholars in the field are concerned that creating plankton blooms could release methane and nitrous oxide, which might increase greenhouse gases. “There are some potentially dangerous side effects,” said Paul G. Falkowski, professor of geology and marine science at Rutgers University.