Researchers are exploring the possiblity of eliminating 7 billion tons of carbon dioxide and other greenhouse gases spewed into the atmosphere each year.

Some ideas include pumping it underground or piping it deep into the ocean.

In 1990, oceanographer John Martin suggested a lack of iron limited the growth of phytoplankton in the equatorial Pacific and Southern Ocean.

"If more iron were added, the populations might explode and ease global warming."

At least three patents have been issued related to ocean fertilization because half of all carbon dioxide-consuming photosynthesis on earth happens at sea.

In the latest research, eight tons of iron slurry were distributed across a five-mile-wide patch of the Southern Ocean about 1,200 miles southwest of Hobart, Tasmania to fertilize growth of ocean algae...

The concept of the experiment is to take advantage of ocean plant life like algae to act like a giant sponge, sopping-up greenhouse gases in the atmosphere...

The algae in turn would consume hundreds of tons of carbon dioxide from the ocean's surface waters and then draw in atmospheric gases to replenish the carbon dioxide.

The idea is only theory that algae oneday could be used to absorb emissions belched from factories, cars and other fossil fuel burners believed responsible for global warming.

Uncertainty exists about what would happen when the algae died?

Would the carbon they absorbed fall to the bottom of the sea?

Researchers can't determine whether the carbon would sink or return back into the atmosphere.

Some researchers fear the unsafe manipulation of nutrients in the sea could cause greater damage...

A study author and oceanographer at New Zealand's National Institute for Water and Atmospheric Research Edward Abraham said: ''I don't think it's a feasible solution to global warming,''

''Even if you could fertilize the entire Southern Ocean and even if all that carbon sank out of the system, it would only use a small fraction of the carbon dioxide that people will pump into the atmosphere over the next 50 years.''

As in previous tests in the equatorial Pacific, phytoplankton and carbon levels increased steadily in the waters over the 13 days of monitoring in 1999.

Satellite data showed the bloom grew to more than 93 miles long after six weeks, accumulating anywhere from 660 to 3,300 tons of algal carbon.

But because of the experiment's tight schedule, nobody could monitor the algae when it eventually died.

It was not clear whether carbon leaked back into the atmosphere or was drawn to the ocean depths.

Also, there is fear the rapid spurt of growth in the fertilized area could affect the waters outside the experimental patch.

Other nutrients like nitrogen and phosphates could be absorbed on a massive scale canceling any positive growth that would have occurred outside.

...or possibility of iron-enriched plankton poisoning other life in the food chain.

''My big concern is that the uncertainties are just incredibly large,'' said Sallie Chisholm, a researcher at the Massachusetts Institute of Technology.