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Fertilizing the oceans to control rising atmospheric CO2 levels
Burning of fossil fuels has resulted in a dramatic increase of this gas over the last 150 years. One of the ways to mitigate the rising atmospheric CO2 levels is to fertilize the oceans with iron. Iron is a critical micronutrient for the growth of phytoplankton. Iron is supplied to the oceans via atmospheric dust and by the hydrothermal fluids from deep-sea vents in the oceans' interior. Iron becomes limiting in the oceanic regions away from the land and its solubility is low in oxic waters. Therefore, the Southern Ocean which is nutrient rich but low in iron concentration is a choice for the scientists for the iron-fertilization experiments. Dr Victor Smetacek (Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven, Germany) explained in his 40th Foundation Year lecture at NIO about the experiment of fertilization of Antarctic waters with dissolved iron solution (EISENEX 1) carried out aboard RV "Polarstern" in early austral spring 2000 in the Atlantic sector of the Southern Ocean. He further added "The large-scale iron fertilization leads to an increase in phytoplankton. The phytoplankton are equivalent to plants on the terrestrial system that take up CO2 to photosynthesize and fix carbon. The increased productivity in oceans provide more food to krill in Antarctic, whose present population is only 10% of the former biomass. Thus, an increase in krill biomass provide beneficial effect on the over-hunted whale stock in the southern Ocean. A large amount of carbon fixed by the phytoplankton blooms sinks to the ocean interior and remain sequestered. The effects of this will be visible in increased zooplankton biomass that in turn will be channeled to higher trophic levels". While speaking about the experiment his team conducted, he further explained that approximately 500 square kilometres of ocean surface were fertilized with iron and the plankton development was followed for 3 weeks. Chlorophyll concentrations increased fourfold inside the patch within 3 weeks after the iron addition. The pigment analyses revealed that this large increase in biomass was caused mainly by the growth of diatoms, which contributed about 75% of the biomass by the end of the experiment. This group of phytoplankton were clearly seen to out-compete other groups present when sufficient iron was made available. Diatom biomass increased dramatically with time inside the iron-fertilized patch following iron addition whereas the abundance of other species remained approximately constant. This experiment demonstrated that phytoplankton react strongly to iron fertilization of waters. The simple food chain of the giants: diatoms -> Krill -> whales is maintained by the giants. As whales are top predators their population size will be food regulated. Thus large-scale iron fertilization experiment will be marine equivalent of ecosystem restoration and maintenance.
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