Geoengineering schemes that aim to slow global warming by seeding oceans with iron to boost carbon dioxide-absorbing phytoplankton may not lead to long-term sequestration of the important greenhouse gas, finds a new study published in the journal Geophysical Research Letters.
The research looked at the impact of the 2010 eruption of Eyjafjallajökull volcano, which released large amounts of iron in the North Atlantic near Iceland. Some researchers speculated that iron fertilization would lead to a large-scale plankton bloom that would absorb massive amounts of CO2 from the atmosphere, helping fight climate change.
The new study however dealt another blow to those hopes. The researchers found that the iron fertilization effect quickly died out due to the rapid depletion of nitrate from the upper layers of the ocean, depriving the phytoplankton of nitrogen, a critical nutrient needed for growth.
“The additional removal of carbon by the ash-stimulated phytoplankton was therefore only 15 to 20 per cent higher than in other years making for a significant, but short-lived change to the biogeochemistry of the Iceland Basin,” said study lead author Eric Achterberg of the National Oceanography Centre in the U.K.
The results are consistent with other research. A 2009 study published in Nature found that carbon uptake after iron fertilization was 80 times lower than suggested by earlier research. That study also involved the National Oceanography Centre.
“You might get a different response if you shock the system by dumping a lot of iron all at once,” Raymond Pollard of the National Oceanography Centre told Nature News at the time. “The effect will still be much smaller than some geoengineers would wish.”
“Ocean iron fertilization is simply no longer to be taken as a viable option for mitigation of the CO2 problem,” Hein de Baar, an oceanographer at the Royal Netherlands Institute for Sea Research in Texel, was quoted as saying by Nature News.
In 2008 Planktos, a private firm which sought to sell carbon offsets from iron fertilization in the ocean, was thwarted by lack of funding after concerns were raised over the environmental impacts. The company’s cofounder conducted an iron fertilization experiment in 2012 despite strong objections from greens.
Eric P. Achterberg at al. Natural iron fertilization by the Eyjafjallajökull volcanic eruption. GEOPHYSICAL RESEARCH LETTERS. Article first published online : 14 MAR 2013, DOI: 10.1002/grl.50221