Estimates of the effect of Southern Ocean iron fertilization on atmospheric CO2 concentrations

IT has been suggested1–3 that fertilizing the ocean with iron might offset the continuing increase in atmospheric CO2 by enhancing the biological uptake of carbon, thereby decreasing the surface-ocean partial pressure of CO2and drawing down CO2 from the atmosphere. Using a box model, we present estimates of the maximum possible effect of iron fertilization, assuming that iron is continuously added to the phosphate-rich waters of the Southern Ocean, which corresponds to 16% of the world ocean surface. We find that after 100 years of fertilization, the atmospheric CO2 concentration would be 59 p.p.m. below what it would have been with no fertilization, assuming no anthropogenic CO2 emissions, and 90–107 p.p.m. less when anthropogenic emissions are included in the calculation. Such a large uptake of CO2 is unlikely to be achieved in practice, owing to a variety of constraints that require further study; the effect of iron fertilization on the ecology of the Southern Ocean also remains to be evaluated. Thus, the most effective and reliable strategy for reducing future increases in atmospheric CO2 continues to be control of anthropogenic emissions.