At sea, however, scientists have learned that phytoplankton are quickly consumed by equally diminutive marine animals, called zooplankton. In a normal ocean environment, without iron fertilization, "the coupling between the plants that grow and the animals that eat them is very tight," Barber said. Plants "rarely get beyond the first day."
For the iron hypothesis to work successfully, photosynthesized carbon in plant material would have to quickly sink to depths between 100 and 300 meters, beyond the range of grazing zooplankton, he said.
However, scientists are finding that iron fertilization also serves to boost zooplankton populations. "They increase in numbers very quickly, but not initially," Barber said.
Results so far suggest iron-fertilized phytoplankton have only one or two weeks to sink or be eaten. After that, zooplankton numbers "increase in a way that they overgraze, just like overgrazing a field," he added.
Once phytoplankton are eaten, carbon assimilated into their tissue would be quickly returned to the atmosphere as carbon dioxide, he said.
If Martin's original hypothesis is ultimately shown to remove significant carbon from the atmosphere, a separate question is whether regulators could find a way to incorporate iron fertilization into a system of "carbon credits." Barber will also discuss that issue at the Seattle meeting.
Under the carbon credit concept included in the framework of the Kyoto Protocol, a factory emitting excess carbon dioxide, for example, could cancel out those emissions by paying for more trees to be planted.
Such an inventory system requires a way of defining and monitoring how much carbon is likely to be stored in a
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Contact: Monte Basgall
monte.basgall@duke.edu
919-681-8057
Duke University
13-Feb-2004