Should the oceans be seeded with large amounts of iron ore that will increase the growth of phytoplankton thatwill consume carbon dioxide? The idea has attracted some support among corporations and foundations looking for ways to minimize the effects of carbon dioxide without changing the world's basic energy generation mix. The idea is simple on its face: iron stimulates the growth of phytoplankton that absorbs carbon dioxide. Ulf Riebesell, a marine biologist at the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany, believes that iron seeding of the oceans could remove 3 to 5 billion tons of carbon dioxide per year, or about 10 to 20 percent of human-generated emissions (Schlermeier, 2003, 110). Patents have been issued for ocean fertilization, and demonstration projects undertaken (Boyd et al., 2000, 695-702; Watson et al., 2000, 730-733).
Nearly half of the Earth's photosynthesis is performed by phytoplankton in the world's seas and oceans (Chisholm, 2000, 685). In the equatorial Pacific and Southern Oceans, Sallie W. Chisholm, a marine biologist at the Massachusetts Institute of Technology, wrote in Nature that it "is possible to stimulate the productivity of hundreds of square kilometers of ocean with a few barrels of fertilizer" (Chisholm, 2000, 686). Atsushi Tsuda and colleagues have studied iron fertilization and have found that, under some circumstances, iron fertilization can dramatically increase phytoplankton mass (Tsuda et al., 2003, 958-961).
In an experiment conducted between Tasmania (near southeastern Australia) and Antarctica, researchers confirmed that vast stretches of the world's southern oceans are primed to explode with photosynthesis but lack only iron. The researchers, who described their work in Nature, said it is too soon to start large-scale iron seeding because the new experiment raised as many questions as it answered. At best, they said, iron seeding would absorb only a small amount of the carbon dioxide in the atmosphere.
These scientists also said that their experimental bloom of plankton was not tracked long enough to determine whether the carbon harvested from the air sank into the deep sea or was again released into the environment as carbon dioxide. "There are still fundamental scientific questions that need to be addressed before anyone can responsibly promote iron fertilization as a climate-control tactic," said Kenneth H. Coale, an oceanographer who has helped design studies of iron's effects in the tropical Pacific (Revkin, October 12, 2000, A-18).
Iron fertilization has some potential problems. First, no way exists to measure the amount of carbon absorbed by phytoplankton. Additionally, the algae produce dimethyl sulphide, which plays a role in cloud formation. Phytoplankton also increases the amount of sunlight absorbed by ocean water, as well as heat energy. It also produces compounds such as methyl halides, which play a role in stratospheric ozone depletion. The iron could promote the growth of toxic algae also which may kill other marine life and change the chemistry of ocean water by removing oxygen. "The oceans are a tightly linked system, one part of which cannot be changed without resonating through the whole system," said Chisholm. "There is no free lunch" (Schlermeier, 2003, 110).
So much iron may be required to produce the desired effect that fertilization of this type will never be commercially useful. "The experiments enabled us to make an initial determination about the amount of iron that would be required and the size of the area to be fertilized," said Ken O. Buesseler of the Woods Hole Oceanographic Institution, who coauthored a study of the idea. "Based on the studies to date, the amount of iron needed and [the] area of ocean that would be impacted is too large to support the commercial application of iron to the ocean as a solution to our greenhouse gas problem," he explained. "It may not be an inexpensive or practical option" (Iron Link, 2003).
Given the limits of present technology, one study estimated that an area much larger than the Southern Ocean (all the Earth's oceans from 50° south latitude to Antarctica) would have to be fertilized to remove 30 percent of the carbon dioxide that human activity presently injects into the atmosphere. Thus, according to this study, "ocean iron fertilization may not be a cheap and attractive option if impacts on carbon export and sequestration are as low as observed to date" (Buesseler and Boyd, 2003, 68).
Despite its problems, iron fertilization is considered possible by some scientists who have fed tons of iron into the Southern Ocean. They reported evidence during 2004 that stimulating the growth of phyto-plankton in this way may strengthen the oceans' use as a carbon sink. In a report published on April 16, 2004, in Science, ocean biologists and chemists from more than 20 research centers said they triggered two huge blooms of phytoplankton that turned the ocean green for weeks and consumed hundreds, perhaps thousands, of tons of carbon dioxide. "These findings would be encouraging to those considering iron fertilization as a global geo-engineering strategy," said Coale. The scientists involved in this experiment, however, are said to "realize that this looked only skin deep at the functioning of ocean ecosystems and much more needs to be understood before we recommend such a strategy on a global scale" (Hoffman, 2004). Other researchers disagree strongly. "From my work, I don't think this could solve a significant fraction of our greenhouse-gas problem while causing unknown ecological consequences," said Buesseler (Hoffman, 2004).
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