Diatom, a type of phytoplankton, as seen by a scanning electron microscope. Photo by: University of Tasmania Scanning Electron Microscope.
For a long time, oceanic iron fertilization was seen as a promising mechanism to combat global climate change. But then in 2009 a well-publicized study found that iron fertilization stored 80 times less carbon than expected, dampening enthusiasm and support around the geoengineering scheme. Now, however, the idea of fertilizing the ocean with iron may be back: a new study in Nature reports that iron fertilization, in the right conditions, could store carbon in the deep ocean for centuries.
Iron fertilization uses the natural ability of marine phytoplankton to store carbon. Researchers dump iron sulphate in parts of the ocean where it is scarce, creating an algal bloom. Days later, when the bloom’s phytoplankton die, they sink to the oceanic floor and, hopefully, take their carbon with them.
“We were able to prove that over 50 percent of the plankton bloom sank below 1000 meter depth indicating that their carbon content can be stored in the deep ocean and in the underlying seafloor sediments for time scales of well over a century”, says co-author Victor Smetacek with the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association.
The researchers attribute the successful results of their study on their marine site, an eddy in the Southern Ocean with significant dissolved silicon, allowing different types of phytoplankton—mostly diatoms—to dominate the bloom.
“This shows how differently communities of organisms can react to the addition of iron in the ocean”, explains co-author Christine Klaas, also with the Alfred Wegener Intistitute.
The scientists note that while their study is promising, much more research is needed to understand how iron fertilization make lock away carbon. Twelves past trials have been attempted with iron fertilization by scientists, but this is the first one to show that a significant portion of the carbon sequestered by the phytoplankton falls with them to the ocean floor, theoretically storing it away.
Critics of iron fertilization, however, fear that the scheme could have untold impacts on marine ecosystems.
Iron fertilization is one of the more well-known and older ‘geoengineering’ schemes to help mitigate or combat climate change by large-scale manipulation of the global environment. However, even proponents of iron fertilization do not see it as a silver bullet. Conducted on a massive scale, the practice would still only sequester a fraction of global annual carbon emissions.
But Smetacek told the Guardian that the geoengineering label shouldn’t scare people away from looking deeper into iron fertilization as one tool among many to combat climate change.
“The time has come to differentiate: some geoengineering techniques are more dangerous than others. Doing nothing is probably the worst option,” he said adding that iron fertilization, in conjunction with other measures, could keep the global climate from a “tipping point.”
While geo-engineering has attracted a lot of attention and controversy in recent years, the vast majority of experts and scientists say the best way to combat global climate change is simply to cut global greenhouse gas emissions produced by burning fossil fuels, deforestation, industrial agriculture, and other human actions.
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