Possible biogeochemical consequences of ocean fertilization

We consider biogeochemical secondary effects that could arise from an increase in ocean productivity, such as may occur via fertilization with Fe. These processes and feedback loops are infrequently discussed in this context, yet are likely to be highly relevant to the understanding of global change in general. In particular, we suggest that increased productivity may increase the production and efflux of greenhouse gases, such as nitrous oxide (N2O) and methane (CH4) and that shifts in phytoplankton species and productivity may cause changes in another climate-related gas, dimethylsulfide (DMS). N2O is also implicated in the destruction of stratospheric ozone. Factors contributing to amplified release include both increased nutrient cycling in general and possible development of low oxygen conditions from fertilization. It is also remotely possible that reduced oxygen from an initial fertilization could mobilize existing Fe pools, inducing uncontrolled self-fertilization. Although lack of relevant physiological and ecological data makes it difficult to provide quantitative limits on the extent of the undesired effects, rough calculations suggest that the enhanced release of N2O alone could totally negate any potential benefit from fertilization and likely worsen global warming and ozone depletion.