The Southern Ocean plays an important role in the exchange of carbon dioxide between the atmosphere and the ocean. One important part of this is the growth of phytoplankton, which act like a natural sponge for carbon dioxide. When these plankton die, they can sink to the bottom of the ocean and thereby store some of the carbon dioxide that they have absorbed. This process has been termed a “biological carbon pump.”
Oceanographers have observed that the Southern Ocean’s waters are not iron-rich and have proposed the idea that adding iron to the Ocean would stimulate phytoplankton growth and thereby boost the biological carbon pump. Some small-scale tests have demonstrated that this actually works. But the idea has been widely debated as a mitigation strategy for climate change. A powerful argument against the idea of seeding the ocean with iron is that there would likely be many unintended consequences to the ecosystem apart from the enhanced growth of phytoplankton and therefore the risks would be unacceptable.
A recent study looked at the effects of increased phytoplankton from natural iron sources like basaltic rocks on the sea animals that feed on them. Some of these are creatures that make shells from calcium carbonate, a process that produces carbon dioxide. This changes the effectiveness of the biological carbon pump. It is unclear how purposefully added iron would impact the process.
Engineering ecosystems to try to mitigate the forces driving climate change is a concept fraught with danger. Extensive studies are essential before employing such a strategy can even be contemplated.
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Iron fertilization less efficient for deep-sea carbon dioxide storage than previously thought?
Photo, posted January 6, 2010, courtesy of Emrys Roberts via Flickr.
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Earth Wise is a production of WAMC Northeast Public Radio.