Implications of large-scale iron fertilization of the oceans

A historical perspective of the scientific study of ocean iron fertilization (OIF) over the last 15 yr prefaces a short synthesis of the multi-faceted issues raised by the 11 contributions to this Theme Section. These issues, which range from ethical to logistical, must be aired in discussions surrounding OIF and its commercial application as a potential climate mitigation tool. Two other issues, not considered in detail by the contributors, are also addressed: (1) the importance of the rate of change in atmospheric CO2 following sustained global OIF (other than model simulations, the only data presently available to assess this comes from the geological record, e.g. Vostok ice core record of dust supply and atmospheric CO2); and (2) the necessity of making realistic estimates of the cost of OIF (i.e. carbon sequestered per unit of iron added) to provide comparisons of the ratio of cost:environmental risk of OIF with other mitigation strategies.