THE most determined attempt to make the ocean soak up more greenhouse gas has failed to make a significant dent.
The Indo-German LOHAFEX iron fertilisation experiment went ahead in the South Atlantic earlier this month, despite an international outcry. Its chief scientists have admitted that it sank only a "modest" amount of carbon dioxide — in the process dampening hopes that the Southern Ocean could cool a warming Earth.
This is likely to add weight to calls for regulations to restrict iron fertilisation schemes.
Ocean fertilisation is an unproven remedy with a range of side effects, according to the Antarctic Climate and Ecosystems Co-operative Research Centre (ACE CRC) in Hobart.
"(It) may cause changes in marine ecosystem structure and biodiversity, and may have other undesirable effects," it said in a paper.
Three hundred square kilometres of ocean was "seeded" with six tonnes of dissolved iron, stimulating the growth of microscopic algae that initially took up the gas.
Antarctic and Southern Ocean Coalition spokeswoman Sian Prior said the experiment should not have gone ahead and, until an international regulatory regime was established, there should be no more.
A US company, Planktos, which advocates selling carbon offsets from ocean fertilisation, praised the experiment's outcome. "We are tickled green that the LOHAFEX ocean replenishment and restoration project has gone so well," it said.
The International Maritime Organisation's London Convention is drafting regulations on ocean fertilisation, which are not believed to support commercial applications.
But the ACE CRC's Tom Trull said he did not believe LOHAFEX would be the last iron fertilisation experiment.
"Certainly the paperwork's going to get more complicated," he said. "My own view is that we should be focusing on what happens using natural situations … rather than going out doing additional experiments."