IT WAS the experiment that many of the scientists taking part hoped would fail. Marine biologists this month produced a 鈥渟tupendous鈥� growth of marine algae by pouring iron into part of the Pacific Ocean. As the algae grew, they consumed large amounts of carbon dioxide from the ocean, 鈥渄rawing down鈥� CO2 from the atmosphere to replace what they consumed. A tonne of iron, in a soup of seawater and iron sulphate, may have extracted up to 10 000 tonnes of carbon from the air.
According to Andrew Watson of the Plymouth Marine Laboratory, one of the leading researchers on the experiment, the scientists fear that the result will encourage 鈥渆co-engineers鈥� who believe the world can counter global warming by repeating the experiment on a vast scale. Iron is probably the limiting factor in the growth of algae in many parts of the ocean.
The joint British-US experiment 鈥渇ertilised鈥� with iron a patch of ocean several kilometres across, between Tahiti and the Gal谩pagos Islands. 鈥淭here was a stupendous effect on the algae, and a dramatic CO2 drawdown,鈥� says Watson, who returned from the South Pacific at the weekend.
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The result, first predicted in 1988 by the late John Martin of Moss Landing Marine Laboratories in California, was unexpected because a similar experiment two years ago failed. Then, according to the leader of both expeditions, Kenneth Coale, also of Moss Landing, small algal blooms did form but they faltered after three days when animal plankton began rapidly eating the plant bloom. Also, much of the iron and the bloom may have sunk. As a result, the experiment failed to absorb much carbon dioxide from the atmosphere (鈥淧umping iron in the Pacific鈥�, New 杏吧原创, 3 December 1994).
After the first experiment, Watson and his colleagues said their results did not support the idea that iron fertilisation would have any significant effect on the amount of CO2 in the atmosphere. The new results turn that conclusion on its head. 鈥淲e don鈥檛 yet know why this year鈥檚 experiment succeeded where last year鈥檚 failed,鈥� says Watson. A likely reason is that the algae in the ocean this summer were different. 鈥淒iatoms benefit most from iron, so it may be there were more diatoms this time. But until our analysis of samples is complete we will not know.鈥�
The second experiment applied a second dose of 鈥渋ron soup鈥� three days after the first 鈥� roughly when the first experiment faltered. This, too, might have made the difference, says Watson.
Joy at the success of the experiment has been tempered by fear that opponents of action to curb emissions of greenhouse gases may use the results to suggest that dosing the oceans with iron may be a cheap and easy 鈥渢echnical fix鈥� for global warming. 鈥淓verybody involved in the experiment is worried about how eco-engineers will use these results,鈥� says Watson. 鈥淢any people were pleased last year when the first attempt failed.鈥�