The great iron dump

The discovery that marine algal blooms deposit organic carbon to the deep ocean answers some — but not all — of the questions about whether fertilizing such blooms is a viable strategy for mitigating climate change. See Article p.313 The iron hypothesis proposes that the supply of iron-bearing dust to certain oceanic regions stimulates phytoplankton blooms that, by sinking out to the deep ocean when the organisms die, sequester carbon absorbed from exchange with the atmosphere. Experiments carried out to test the idea have provided clear evidence that iron addition generates phytoplankton blooms in waters with high -nutrient but low -chlorophyll concentrations, as proposed. But the fate of phytoplankton blooms and hence the extent of any carbon sequestration to the deep ocean has remained uncertain. This paper presents multiple lines of evidence, collected by aboard RV Polarstern in 2004 during the European Iron Fertilization Experiment (EIFEX), that suggest carbon is exported to the deep ocean as a result of iron fertilization, with at least half of the bloom biomass sinking to below 1,000 metres.