Questions raised over ocean fertilisation
News analysis A new report suggests there are still huge scientific uncertainties around how much carbon dioxide could be sequestered by adding iron to the oceans to stimulate plankton blooms.
The researchers studied an area where natural phytoplankton blooms occur around the Crozet Islands in the Southern Ocean, 2200 kilometres southeast of South Africa.
Volcanic rocks on the islands naturally supply the area with iron and the concentration of iron slowly peters out to the south.
Eventually, the concentration of iron is so low that that there is not enough to support much phytoplankton.
Scientists are currently involved in "geo-engineering" experiments to artificially "fertilise" these areas with iron to stimulate CO2-consuming phytoplankton as a means of sequestering greenhouse gases.
One question they are trying to answer is how much carbon captured by phytoplankton is actually removed from the food chain to the deep water, so it isn't re-released into the atmosphere shortly after being removed.
Viability of geoengineering
Pollard and colleagues found that the more iron in the water, the more carbon is exported to the deep ocean.
But their results also question the findings of some previous studies about how much carbon can be sequestered in this way.
Pollard and colleagues found that by one measure the amount sequestered was 15-50 times short of some estimates given by researchers studying geo-engineering.
"Obviously it's that much less viable or less attractive. You would have to add 15 times more iron to get the same effect in carbon," says Pollard, adding he is confident of the numbers.
Pollard says these figures apply to carbon sequestered at 200 metres, which would probably be released to the surface again in 10 years or less.
He says longer-term sequestering would require the carbon to sink to much greater depths.
"We made measurements at 3000 metres deep and there the numbers are much smaller."
Pollard says the drop off in carbon at greater depths is partly because the carbon changes form as it sinks deeper. He says figures sometimes quoted don't take such variables into account.
"Geoengineers tend to quote numbers that were found in ideal laboratory experiments of some years ago, which are rather higher," he says.
The figures for sequestration obtained by Pollard were also higher than those found in other geoengineering experiments and he says it is possible that the natural system may not reflect what happens in artificial systems.
An Australian marine biologist specialising in phytoplankton, Dr Martina Doblin of the University of Technology Sydney, says the accumulating evidence shows there is a lot of scientific uncertainty around how much carbon can be sequestered by iron fertilisation.
She says this will make it hard for companies interested in developing ocean fertilisation technology to convince investors to support them at this stage.
Like many scientists, Doblin thinks some ocean fertilisation plans, especially those involving the addition of nitrogen, are too risky. But she thinks research into iron fertilisation is important.
"We do have a critical need to do something about climate change and this is one option that needs to be explored," she says.
But Doblin says she is concerned about unregulated commercially-driven research, which is kept secret and aimed at boosting share prices.
According to experts at the Antarctic Climate and Ecosystems CRC in Hobart, the addition of iron may alter marine ecosystems and if the practice becomes widespread, it may lead to an increase in methane and nitrous oxide emissions.
Last year the Convention on Biological Diversity (CBD), urged caution on ocean fertilisation, calling for it to be limited to small scale scientific research studies.
A German/Indian government-sponsored LOHAFEX experiment this week began seeding 300 square kilometres of sea in the South Atlantic with 20 tonnes of iron sulphate.
Some civil society groups, such as the Canadian-based ETC Group, say projects such as LOHAFEX contravene the CBD.
Press reports say the German Federal environment minister Sigmar Gabriel has called for the research to stop, despite the project being given the go-ahead by the research minister.
One US-based company involved in investigating iron fertilisation technology, Climos, cites the International Marine Organization's London Convention as the appropriate authority governing geo-engineering.
Last year, a London Convention meeting agreed only "legitimate scientific research" should be allowed, but further specification of what constitutes legitimate research is yet to be agreed.
Climos CEO Dan Whaley says experiments need to be "scaled up" to see how the technology really works and says his company is interested in funding government scientists to do this work.
"I think what needs to happen over the next several years are a series of truly scientific research projects with no commercial outcome in order to better understand the long-term potential [of the technology]," says Whaley.