Efficiency of carbon sequestration by added reactive nitrogen in ocean fertilisation

Addition of limiting nutrients to the surface waters of the deep ocean will lead to increased photosynthesis and associated biological productivity. Some of carbon taken up by phytoplankton will sink to the deep ocean, providing sequestration of carbon in the deep ocean. This paper considers nitrogen as the added nutrient and determines the losses in this sequestration process, taking into account a number of mechanisms. Other factors that impact on carbon sequestration are also taken into account, such as production of other greenhouse gases, and manufacture and distribution of nutrient. The overall efficiency of the sequestration process is found to be approximately 75%, depending on the form of the nutrient. That is, up to 75% of the carbon processed by photosynthesis (on adding nitrogen) can be sequestered. This is well in excess of sequestration estimates using iron as the added nutrient.