By Richard Black
Environment correspondent, BBC News website
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.
Germany's environment ministry had tried to stop the project, which green campaign groups said was "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some of the excess carbon dioxide - put it back where it came from, in a sense, because the petroleum we're burning was originally made by the algae," said Victor Smetacek from the Alfred Wegener Institute in Bremerhaven.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."