A possible solution to global warming may be further away than ever, according to a new report published in the journal Nature. Scientists measuring how much of the greenhouse gas carbon dioxide is locked away in the deep ocean by plankton when it dies found that it was significantly less than previous estimates.
Image courtesy of University of PortsmouthPlankton is a natural sponge for carbon dioxide. It occurs naturally in the ocean and its growth is stimulated by iron which it uses to photosynthesise and grow. When plankton dies it sinks to the bottom of the ocean locking away some of the carbon it has absorbed from the atmosphere.
Fertilising plankton by the artificial addition of iron has long been proposed as a potential way to geo-engineer the removal of carbon dioxide from the atmosphere.
Researchers analysed an area of the Southern ocean known to be naturally rich in iron and their report reveals that the amount of carbon sequestered to the deep ocean for a given input of natural iron falls far short of previous geo-engineering estimates. This has serious implications for proposals to influence climate change through iron fertilisation of the sea.
Yet some researchers believe that the theory should not be discounted and that more research is needed.
Dr Gary Fones is a marine biogeochemist at the University of Portsmouth’s School of Earth and Environmental Science. He was part of the team which carried out the study around the Crozet islands in the Southern ocean.
He said: “We know that carbon is transported to the deep ocean and seabed via the plankton, but the question is how much and for how long?” The combined results of all the studies undertaken so far indicate that there could be other factors influencing the amount of carbon exported.
“No-one has found a solution yet to tackle the issue of global warming and further research is needed to determine exactly what’s going on, particularly with regards to iron fertilisation.”
The report is timely as it coincides with the recent halt of a controversial Indo-German expedition also in the Southern Ocean. Just days ago, a ship carrying scientists from India and Germany were prevented from dumping iron into the sea as part of an experiment to artificially fertilise the ocean and stimulate phytoplankton growth.
Reports suggest that the German government suspended the operation following claims by green campaigners that it breaches a UN moratorium on ocean fertilisation. But the scientists involved believe that legitimate scientific experiments were specifically approved by the Convention for Biological Diversity (CBD) and they assert that the research is crucial to understanding more.
Dr Fones agrees. He argues that the experiment is not so-called geo-engineering for profit but is part of an important piece of research. He said:
“Efforts to find a solution to global warming are under threat by those people who are most concerned about climate change. But legitimate experiments like this one are crucial to learning more about the effects of iron fertilisation and will help scientists evaluate the merits of such a scheme.”
He agrees that adding iron in large quantities could potentially damage the whole biological food chain but argues that the German-Indian experiment is literally a drop in the ocean. Experiments like this will have a minimal impact on the surrounding area but will massively further our understanding of the science.”
Ocean climate fix remains afloat
James Morgan, BBC News 29 Jan 09;
Plans to curb climate change by using plankton to draw carbon dioxide into the world's oceans have been boosted.
A spectacular natural algal bloom in the Southern Ocean helped to "lock" carbon away into deep sea sediments, according to a study in Nature journal.
But the amount of carbon stored was not nearly as high as some artificial "geo-engineering" schemes had predicted.
Plans to "seed" plankton blooms by adding iron to oceans are strongly opposed by many green groups.
The international research team behind the Crozex study say their findings have "significant implications" for plans to mitigate climate change.
They come as scientists resume a controversial ocean fertilisation experiment in the Scotia Sea, east of Argentina.
The Lohafex study had been suspended by the German government after environmental groups protested that it violates the terms of the UN Convention on Biological Diversity.
They fear that adding iron to oceans may damage ecosystems.
Ocean commotion
Using algae as a "biological carbon pump" has been touted as one of the more promising "geo-engineering" schemes for mitigating global warming.
Plankton act as a natural sponge for carbon dioxide - drawing the greenhouse gas down out of the atmosphere and into the sea.
When plankton die, they sink to the bottom of the ocean, locking away some of the carbon they have absorbed.
Experiments suggest that "seeding" oceans with iron can stimulate the growth of plankton - particularly waters which are rich in nutrients.
But exactly how much carbon sinks to the sea floor, and how long it remains locked away, is still unknown.
In the Crozex experiment, an international research team sailed to the Crozet Islands, in the Southern Ocean, about 2,200km (1,400 miles) southeast of South Africa.
These waters experience a spectacular annual plankton bloom the size of Ireland, 120,000 sq km (46,300 sq miles) fertilised by iron naturally supplied from the islands' volcanic rocks.
The researchers used sediment traps to follow the passage of carbon from the sea surface to the ocean floor.
They found that seawater and sediment samples taken directly beneath the bloom were two-to-three times richer in carbon, compared to samples from a nearby ocean region which was rich in nutrients, but not in iron.
"Our results have significant implications for proposals to mitigate the effects of climate change through purposeful addition of iron to the ocean," said lead author Professor Raymond Pollard, of the National Oceanography Centre, Southampton.
"Our findings support the hypothesis that increased iron supply...may have directly enhanced carbon export to the deep ocean.
"[However] our estimate of carbon sequestration for a given iron supply still falls 15-50 times short of some geo-engineering estimates."
Next steps
"This is a significant result," said Professor Peter Burkill, director of the Sir Alister Hardy Foundation for Ocean Science, Plymouth (SAHFOS).
"It suggests that ocean iron fertilisation might work for reducing atmospheric CO2 through export of carbon into the ocean's interior.
"But the next step from natural experiments to artificial ones is crucial.
"We now need to know what the ecological impacts of artificial fertilisation experiments are."
Many scientists doubt whether adding iron artificially will ever seed plankton blooms as successfully as natural iron.
To test the technique, the German government has just re-authorised one of the largest ocean fertilisation experiments to date.
The Lohafex expedition had been suspended, after concerns that it violated the terms of the Convention On Biological Diversity.
But researchers on board the vessel RV Polarstern have now begun seeding six tonnes of iron sulphate over 300 square kilometres of the Scotia Sea, east of Argentina.
"As this paper shows, much larger amounts of iron are being added daily by natural processes around the Crozet Island," said Professor Andrew Watson, University of East Anglia.
"And that doesn't seem to have done the Antarctic ecosystem any harm."
Crucial experiment
"Legitimate experiments like [Lohafex] are crucial to learning more about the effects of iron fertilisation," said Dr Gary Fones, University of Portsmouth, who was part of the Crozex team.
"They will help scientists evaluate the merits of such a scheme."
However, the environmental impact of Lohafex was questioned by Kristina Gjerde, high seas policy advisor, the International Union for Conservation of Nature (IUCN).
She said: "The fundamental question remains, should this activity be allowed to proceed unregulated?
"I am not against research in this area; however, it should follow internationally agreed rules and procedures.
"The Convention on Biological Diversity's call for a defacto moratorium on ocean fertilisation reflects the will of the international community that this activity should not proceed until certain basic requirements have been satisfied.
"The government ministries that authorised the Lohafex experiment did not comply with the rules for [environmental] impact assessments as they currently exist under the London Convention [on the Prevention of Marine Pollution]."