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Science: Debate Continues Over LOHAFEX Results

Science Blogs covers the debate over the LOHAFEX results, which showed poor carbon sequestration as a result of fertilizing an eddy very poor in silica. Diatoms cannot grow without silica, and are the primary engines of the biological pump.

"But biogeochemist Kenneth Coale, director of Moss Landing Marine Laboratories in California, estimates that the silicon-rich southern part of the Southern Ocean would deliver up to twice as much potential carbon sequestration as the northern area Smetacek fertilized, in large part because of the diatoms and associated ecosystem dynamics. The predators that eat diatoms, it turns out, have large waste pellets that sink rapidly. Coale warns that calling iron fertilization a failed strategy on the basis of an experiment in low-silicon waters is just as unwise as declaring the technique a home run after a successful experiment would have been. "I would be reluctant to extrapolate from any one experiment anything having to do with the efficacy of iron fertilization as a carbon-sequestration strategy," says Coale.

"Another scientist, Margaret Leinen, is the head of a company, Climos, that is hoping to commercialize iron fertilization to gain carbon credits at sea. The former head of geosciences at the National Science Foundation, she says the 1-gigaton-a-year figure for atmospheric CO2 was based on paleoclimate records. Chemical analyses of ocean cores show that the Southern Ocean drew down at least that much CO2 millions of years ago during glacial periods. "In the paleorecord, we find a lockstep correlation between the amount of [phytoplankton growing] and temperature," says Coale.

"Smetacek had actually tried to find an area of ocean that would feature diatoms. Levels of silicon are generally higher south of 50° latitude. But Smetacek says the German government asked him to stay north of that line due to a treaty called CCAMLR designed to protect marine species in the Southern Ocean. Part of that restriction was no doubt connected to the fact that the LOHAFEX mission was controversial from the start, drawing criticism both from environmentalists and from the German environmental ministry. So Smetacek says he had to settle on a patch at 48° south latitude.

Category: Ocean Fertilization
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