NZ scientist scuttles own ocean theory

Further research by a Dunedin oceanographer has torpedoed a theory that fertilising microscopic plants in the oceans could cut a build-up of excess carbon dioxide in the atmosphere.

Iron fertilisation of plants in the surface ocean may not be the answer to removing excess "greenhouse gas" carbon dioxide from the atmosphere, according to a paper by Dr Philip Boyd and overseas researchers, published by the academic journal Nature.

Some commentators had suggested that fertilising the world's oceans would slash atmospheric carbon dioxide and provide an answer to global warming perils.

Dr Boyd is based at the National Institute of Water and Atmospheric Research Centre for Chemical and Physical Oceanography at the University of Otago chemistry department.

An iron fertilisation experiment done in the Southern Ocean in 1999 by Dr Boyd and a team of New Zealand and international scientists had such dramatic results - a five-fold increase in phytoplankton stocks during the developing bloom - it was thought that adding iron might boost the amount of atmospheric carbon dioxide locked up in the ocean.

But a more recent, longer-term fertilisation experiment led by Dr Boyd, in the Gulf of Alaska, showed that after 18 days, the iron-induced bloom declined and satellite pictures showed merely "a ghost of the plankton-rich patch that blossomed initially".

Reduced iron supply had cut the bloom, but the removal of all of the silicate by phytoplankton was also a secondary factor, Dr Boyd said.

Iron could be used to stimulate phytoplankton growth but for every tonne of iron, scientists would have to add "at least 5000 tons of silicate to enable the blooms to persist".

- NZPA