Last summer scientists proposed an imaginative but radical solution to the buildup of carbon dioxide in the atmosphere, which many researchers fear could lead to global warming.

Why not, they asked, dump hundreds of thousands of tons of iron fertilizer into the ocean and so create a giant bloom of marine algae? The growing algae would suck carbon dioxide out of the atmosphere and sequester it in the sea. The algae in the Southern Ocean around Antarctica appear to be starving for iron. Scientists half-jokingly called their scheme the "Geritol Solution."

Alas, the Geritol Solution might not work. According to a computer simulation reported in the current issue of the journal Nature, a spurt of algal growth would not be sustained because in the Southern Ocean, the surface waters, where all the action is, are not replaced quickly enough by deeper water that contains other needed nutrients such as phosphorus and nitrogen.

In other words, the algae in the surface water might have all the iron they need, but there may not be enough mixing of the exhausted surface water and nutrient-rich deep water to sustain accelerated growth.

Wallace Broecker of Columbia University and T. H. Peng of Oak Ridge National Laboratory conclude that "even if iron fertilization worked perfectly, it would not significantly reduce atmospheric carbon dioxide content."