Keywords:Ocean fertilisation, Sequestration, Carbon Sink
In order to meet the goal of limiting global average temperature increase to less than 2 °C, it is increasingly apparent that anthropogenic CO2 sinks of up to 10 Pg C yr-1 will be needed before the end of the century. Ocean iron fertilization, although controversial has been shown to be one of the few technologies with a large capacity for removing CO2 from the atmosphere. Here I present the findings of a study to assess the capacity of an alternate form of ocean fertilization, Ocean Macronutrient Fertilisation (OMF). Sufficient phosphate exists outside the iron limited surface ocean to support once-only sequestration of up to 3.6 Pg C by fertilization with nitrogen. Ongoing sequestration using nitrogen fertiliser is estimated at 1.07±0.27 Pg C yr-1. If N and P were used in combination to fertilise the ocean, the size of the CO2 sink thus created is limited by societies willingness to utilize phosphate resources. Doubling current phosphate production would allow an additional 0.9 Pg C yr-1 sequestration and consume 0.07% yr-1 of known global resources. Environmental risks have received little quantitative evaluation; however it is likely they could also limit the scale of implementation.