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Could dumping iron in the oceans slow global warming?

Using iron fertilizer to create algae blooms could help our oceans absorb more carbon dioxide from the atmosphere, say researchers.

By Wynne ParryLiveScience Senior Writer / July 18, 2012

This species of diatom, Corethron pennatum, bloomed during the iron fertilization.

Marina Montresor, SZN / Alfred Wegener Institute

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Some hope fertilizing tiny, floating plants in the ocean, prompting them to suck carbon dioxide out of the air, could help solve global warming.

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A new experiment confirms this controversial idea has some merit, although important questions remain.

Using an eddy in the Southern Ocean near Antarctica, researchers used iron fertilizer — the sort used to improve lawns — to create a man-made algal bloom. In the weeks that followed, researchers say, this bloom funneled a significant amount of Earth-warming carbon down into the ocean's depths, where it will remain sequestered for some time, unable to contribute to global warming.

This experiment provides some important insight into this potential approach to combating climate change, said Ken Buesseler, of the Woods Hole Oceanographic Institution, writing in Thursday's (July 19) issue of the journal Nature.

A potential solution?

This general approach, modifying the planet to address climate change, is known as geoengineering, and, geoengineering proposals like iron fertilization tend to raise many uncertainties and risks. Other geoengineering ideas have included pumping aerosols into the atmosphere to block out solar radiation or tucking away excess carbon in underground reservoirs. [Top 10 Craziest Environmental Ideas]

Ocean fertilization is a controversial idea, prompting protest from those who fear the unintended environmental impacts it may have.

"Most scientists would agree that we are nowhere near the point of recommending [iron fertilization of the oceans] as a geoengineering tool. But many think that larger and longer [iron fertilization] experiments should be performed to help us to decide which, if any, of the many geoengineering options at hand should be deployed," Buesseler wrote.

Phytoplankton, which includes microscopic marine plants and photosynthetic microbes, blooms naturally in the ocean. However, in seawater, there is only limited iron, an element these organisms need to grow, so by adding iron to seawater, it's possible to make a man-made bloom.

In this study, the researchers fertilized an eddy because it offered a largely self-contained system, or "a gigantic test tube," said lead researcher Victor Smetacek, with the Alfred Wegener Institute for Polar and Marine Research in Potsdam, Germany.

By mixing an iron fertilizer into the seawater, the researchers created the equivalent of a good-size spring bloom like those seen in the North Sea or off Georges Bank off the New England coast, which turned the water from blue to turquoise, Smetacek said.

Moving carbon

The team found that after they added the iron, the levels of nutrients, including nitrogen, phosphorus and silicic acid, which algae called diatoms use to construct their glass shells, declined until around 24 days after the fertilizer was added.

Dissolved inorganic carbon, which normally remains in equilibrium with the carbon dioxide in the atmosphere, also declined more quickly than it could be replaced by the carbon dioxide in the atmosphere.

Meanwhile, their measurements revealed particulate organic matter, including the silica the diatoms used to make their shells, and chlorophyll, the green pigment used in photosynthesis, increased within the surface waters.

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