Export is not enough: nutrient cycling and carbon sequestration

The question of whether ocean iron fertilization (OIF) can yield verifiable carbon sequestration is often cast in terms of whether fertilization results in enhanced particle export, However, model studies show that oceanic carbon storage is only weakly related to global particle export-depending instead on an increase in the carbon associated with the pool of remineralized nutrients. The magnitude of such an increase depends on circulation, stoichiometric ratios and gas exchange. We argue that this puts serious challenges before efforts to properly credit OIF that must be taken into account at the design stage.