Ocean Fertilisation Phil. Trans. Roy. Soc.: 13 th June 2008 1 Ocean Fertilisation: a potential means of geo-engineering? Lampitt R.S., Achterberg E.P., Anderson T.R., Hughes J.A., Iglesias-Rodriguez M.D., Kelly- Gerreyn B.A., Lucas M*., Popova E.E., Sanders R., Shepherd J.G., Smythe-Wright D., Yool A. All authors except * at: National Oceanography Centre, European Way Southampton SO14 3ZH, UK * Department of Oceanography, University of Cape Town, Rondebosch, Cape Town, 7701, South Africa Abstract The oceans sequester carbon from the atmosphere partly as a result of biological productivity. Over much of the ocean surface this productivity is limited by essential nutrients and we discuss whether it is likely that sequestration can be enhanced by supplying limiting nutrients. Various methods of supply have been suggested and we discuss the efficacy of each and the potential side effects that may develop as a result. Our conclusion is that these methods have the potential to enhance sequestration but that the current level of knowledge from the observations and modelling carried out to date does not provide a sound foundation on which to make clear predictions or recommendations. For ocean fertilisation to become a viable option to sequester CO 2 we need more extensive and targeted field work and better mathematical models of ocean biogeochemical processes. Models are needed both to interpret field observations and to make reliable predictions about the side effects of large scale fertilisation. They would also be an essential tool with which to verify that sequestration has effectively taken place. There is considerable urgency to address climate change mitigation and this demands that new field work plans are developed rapidly. In contrast to previous experiments, these must focus on the specific objective which is to assess the possibilities of CO 2 sequestration through fertilisation. Keywords: Ocean fertilisation, iron, nutrients, carbon sequestration.