Setback for climate technical fix

By Richard Black Environment correspondent, BBC News website

The experiment may have been compromised by voracious amphipods

The biggest ever investigation into "ocean fertilisation" as a climate change fix has brought modest results.

The idea is that putting iron filings in the ocean will stimulate growth of algae, which will absorb CO2 from air.

But scientists on the Lohafex project, which put six tonnes of iron into the Southern Ocean, said little extra carbon dioxide was taken up.

The German environment ministry and campaign groups had tried to stop the project which they called "dangerous".

Leaders of the German-Indian expedition said they had gained valuable scientific information, but that their results suggested iron fertilisation could not have a major impact, at least in that region of the oceans.

"There's been hope that one could remove some of the excess carbon dioxide - put it back where it came from, in a sense, because the petroleum we're burning was originally made by the algae," said Victor Smetacek from the Alfred Wegener Institute in Bremerhaven.

"But our results show this is going to be a small amount, almost negligible."

Food chain

Previous experiments, which have been going on for at least a decade, had indicated that iron particles could stimulate the growth of phytoplankton - algae - and that when the phytoplankton died, they fell to the sea floor, meaning that carbon taken from the air was effectively locked away on the bottom of the ocean.

Following fertilisation of a 300 sq km patch of ocean, Lohafex, too, saw a burst of algal growth.

But within two weeks, the algae were being eaten by tiny creatures called copepods, which were then in turn eaten by amphipods, a larger type of crustacean.

The net result was that far less carbon dioxide was absorbed and sent to the sea floor than scientists had anticipated.

"What it means is the Southern Ocean cannot sequester the amount of carbon dioxide that one had hoped," concluded Professor Smetacek.

Satellites can spot phytoplankton blooms in the process of formation

One key issue appears to be the type of algae that grows in response to the extra iron.

Earlier experiments had found diatoms blooming - organisms with a protective silicate casing.

But in the Lohafex area, the diatom population could not increase because the waters were depleted of silicon.

Some scientists have long argued that the iron fertilisation vision was flawed because lack of iron was not always the factor limiting growth; and this result appears to back that contention.

Growing concerns

The Lohafex expedition, which used the German Polarstern ship, was controversial from the outset, with Greenpeace leading demands that it be stopped.

The campaign group said tipping iron filings into the sea amounted to pollution, and was forbidden under international agreements including the UN Convention on Biological Diversity, which at its 2008 meeting had called for a de facto moratorium on such experiments except at small scale in coastal waters.

"There are two things that concern us," said Greenpeace scientist David Santillo.

"Firstly, there's the direct impacts from the experiments themselves, and as the scale of the experiments has gone up and up there's much greater potential for those direct results," he told BBC News.

"But a second and broader concern is that if we're going to be pursuing this as a climate mitigation strategy, then we're looking at a state of the world where we rely on manipulating the ocean on a truly huge scale and that would undoubtedly have large and possibly irreversible effects on ocean ecosystems."

The German government put the expedition on hold earlier this year because of these concerns, but subsequently allowed it to proceed.

A commercial company, Climos, is planning a much larger experiment that could cover up to 40,000 sq km of ocean.

It hopes eventually to receive funding through the global carbon market if it can demonstrate that the technique can sequester large quantities of the greenhouse gas.