For a cooler world

 
Published: Friday 15 November 1996

it could take something as simple as iron supplements to combat the spectre of global warming. It was John H Martin, an ocean scientist who had first suggested that fertilising the seas with thousands of tonnes of iron compounds could result in the sudden spurt of marine plant organisms called phytoplanktons (example algae) which would gobble up huge amounts of carbon dioxide ( co 2 ) dissolved in sea water, not unlike terrestrial plants removing co 2 from the air. Reducing co 2 , a prime greenhouse gas in the atmosphere, would lead to a cooler world, the proposal surmised.

A panel of the National Research Council, deciding to put to test this suggestion, first undertook a small-scale experiment in 1993. However, this experiment failed before the 'plankton boom' could be observed. A second experiment, Iron-Ex ii, was started in 1995. The results have been assessed now and show that there could be some truth behind Martin's hypothesis. In a recent issue of Nature , four different groups record their observations of seeding about 65 sq km of the equatorial Pacific, some 1,600 km west of Ecuador, with 454 kg of ferrous sulphate.

Previously starved populations of planktons increased 30-fold a few days after the seeding. "We had an explosion of phytoplankton that was almost biblical in proportions," says Kenneth S Johnson of Moss Landing, Marine Laboratories in California, "and the water went from clear blue to this green, soupy-looking mess." The flow of co 2 , which would normally pass from the uppermost layer of the sea into the atmosphere, also reduced by 60 per cent. According to two research teams from the Plymouth Marine Laboratory and the University of East Anglia, uk , fertilising the Southern oceans alone could lower the atmospheric co 2 concentration by six to 21 per cent.

Using iron can also result in an additional cooling effect beyond co 2 reduction. The amount of a critical gas called dimethyl sulfide ( dms ) that is produced in considerable quantity by a well-fed plankton is released into the water. dms later rises into the air and is transformed into aerosol sulphuric particles, which serve as condensation points for clouds. And clouds are important for controlling the earth's surface temperature by shading the ground and reflecting incoming solar radiation.

However, scientists voice a cautious note. A worldwide iron seeding scheme, if ever devised, could lead to a disturbance of the marine food chain and the consequences could be devastating. "You would certainly have a huge shift in the ecosystem and not all of it good," said Johnson.

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