A method for verifying carbon storage in seawater to which a growth stimulant has been supplied for stimulating a bloom of nitrogen fixing organisms for enhancing carbon storage therein, comprises selecting a region of seawater including a surface mixed layer, a euphotic zone extending below the surface mixed layer, and a plurality of deeper zones; determining the effect of growth stimulant on the rate of nitrogen fixation and carbon transport in the region; and determining the amount of carbon stored at different depths and projected duration of carbon storage at each of the depths.