Carbon dioxide levels in the atmosphere have been climbing steadily, from 200 parts per million (ppm) 18,000 years ago to a pre-industrial level of 280 ppm. Today the figure is around 370 ppm.
The rapid increase in atmospheric carbon dioxide is almost entirely attributable to human activities. The increase concerns scientists because of the likelihood that the trapped gases in the atmosphere will create a "greenhouse" effect, increasing average global temperatures.
There are basically only two ways to decrease carbon dioxide levels: reduce emissions or create more carbon sinks.
The "Geritol solution" suggests that actively fertilizing the Southern Ocean with massive amounts of iron would spur the growth of phytoplankton, thus creating a giant carbon sink.
Upwelled Iron Hypothesis
Filippelli and Latimer, a doctoral student at IUPUI, argue that the excessive iron that spurred major phytoplankton blooms in the past is not the result of an external factordustbut comes from inside the ocean itself.
During ice age intervals, glaciers recede and much more land is exposed. Rivers end up dumping the silt, mud, and clay they carry directly into the ocean rather than it being filtered by deltas. As a result, the "dirt load" in the ocean increases significantly, the two researchers say.
"About 80 percent of the sediment that would be deposited on the continental margins during a glacial period goes right into the sea," said Filippelli. This sediment is swept along in ocean currents that begin in Greenland and continue down through the North Atlantic, staying in the deep sea for hundreds of years.
A problem with the Geritol solution, said Filippelli, is that "the ocean strips away iron really quickly."
Experiments in which dissolved iron was dumped on the surface of the ocean showed that the iron was concentrated in the region only a week or two before circulation caused it to disburse through dilution or downwelling (sinking from the light-filled surface ocean), Filippelli explained. "It would take massive amounts of iron to sustain bloom productivity," he said.
He noted, however, that several patent applications are pending for delivery systems that would keep iron added to the ocean from being disbursed so widely that it would fall to concentrations too low to spur phytoplankton growth.
The Geritol solution worries environmentalists. "We just don't know the long-term implications of deliberately altering" such a massive ecosystem, Filippelli argued.
"There's very little regulation right now of what you can do in the open ocean," he said, "and as long as you have people hoping to make a profit off of creating a carbon sink, you have the potential for a problem."
If the source of the iron is silt carried in the huge hemipelagic load created by the ending of an ice age, and it is being delivered by waters upwelling from the deep ocean, "the Geritol solution is just not going to work," Filippelli said.
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