Abstract

Various geoengineering approaches are currently being considered to arrest the build-up of CO2 in the atmosphere. Of these, ocean fertilisation by the addition of iron is receiving considerable attention, including significant commercial interest and activity. Provisionally the evidence from the 12 mesoscale iron addition experiments appears promising as these have all stimulated phytoplankton growth, with the resulting blooms often visible in satellite ocean colour images. However evidence for the subsequent increased transfer of the additional particulate carbon into the deep ocean is limited. Furthermore, analysis of iron:carbon ratios and models of large-scale ocean fertilisation indicate that the effectiveness of carbon sequestration is less than initially estimated. The feasibility of large scale fertilisation, in terms of practicality and verification, presents major challenges and potential side-effects such as enhanced trace gas production, oxygen depletion and far-field nutrient depletion remain areas of concern. Until recently international legislation on ocean fertilisation has been lacking, although efforts are now underway to include ocean fertilisation in an amendment to the London Convention on Dumping. This talk will examine the results of previous iron addition experiments in the context of ocean fertilisation, and the issues relating to its application as a geoengineering option for ocean carbon sequestration.