Iron Fortification: Lots of Insight, Little Prediction
Previous attempts to stimulate phytoplankton production via artificially supplied iron have brought important, albeit limited, insights into the material cycles of the oceans, say Philip Boyd from the University of Otago in New Zealand and colleagues. In view of the short duration and problems in extrapolating the data to a global scale, it is not yet possible to predict with certainty whether this approach will be able to buffer the rising carbon dioxide values.
In the early 1990s, oceanographer John Martin came up with the idea that iron restricted the growth of plankton in otherwise nutrient-rich ocean regions. If this deficiency is remedied, the algae stocks should literally explode - and bind the greenhouse gas carbon dioxide in their biomass: fertilizing against global warming. Since then there have been numerous experiments with ships, but also soon more extensive experiments in which different amounts of iron s alts and a tracer molecule were added to the mixed surface layers one or more times over the course of days (FeAXs - Fe addition experiments). In addition, scientists studied natural algal blooms in such high nutrient, low chlorophyll (HNLC) areas at Galapagos, in the Circumantarctic Current and near the Crozet Islands and the Kerguelen Islands.
As Boyd and his colleagues now state in a review of the activities to date, they were able to demonstrate iron as a limiting factor in a third of the world's oceans with these twelve experiments. However, future experiments would have to run with more precisely coordinated methods of iron addition and also over longer periods of time. This is the only way, for example, to determine the efficiency of fertilization: How much carbon is bound with how much iron is used and withdrawn from the system by sinking to the depths.(af)
