Berlin - Germany gave the green light on Monday to a controversial plan with India to drop six tons of iron dust into the Antarctic Ocean.

The experiment is the biggest trial ever of iron fertilization, a technology which could stop global warming at very little cost.

Following complaints by environmentalists, Germany's Science Ministry ordered the plan suspended while it conducted an urgent review.

"After careful a study of expert reports, I am convinced there are no scientific or legal objections to the German-Indian marine research project," Science Minister Annette Schavan said Monday.

Under the scheme, the iron dust is to be sprinkled over an area of 300 square kilometres from a German research vessel, the Polarstern.

It is hoped that algae living at the ocean surface will soak up the iron and reproduce rapidly, absorbing carbon dioxide from the surface water.

At the end of their life cycle the algae die and sink. Most of the carbon ends up in deep water or on the sea bottom.

The ocean absorbs more carbon dioxide from the air, reducing the greenhouse effect. Sequestering carbon this way might stop global warming.

Thirty Indian scientists and 18 from other nations left on board the Polarstern from Cape Town on January 7 to carry out the experiment. (dpa)