Ocean iron fertilization is an example of a geoengineering technique.[1] Iron fertilization[2] attempts to encourage phytoplankton growth, which removes carbon from the atmosphere for at least a period of time.[3][4] This technique is controversial because there is limited understanding of its complete effects on the marine ecosystem,[5] including side effects and possibly large deviations from expected behavior. Such effects potentially include release of nitrogen oxides,[6] and disruption of the ocean's nutrient balance.[1] Controversy remains over the effectiveness of atmospheric CO 2 sequestration and ecological effects.[7] Since 1990, 13 major large scale experiments have been carried out to evaluate efficiency and possible consequences of iron fertilization in ocean waters. A study in 2017 determined that the method is unproven; sequestering efficiency is low and sometimes no effect was seen and the amount of iron deposits that is needed to make a small cut in the carbon emissions is in the million tons per year.[8]
Approximately 25 per cent of the ocean surface has ample macronutrients, with little plant biomass (as defined by chlorophyll). The production in these high-nutrient low-chlorophyll (HNLC) waters is primarily limited by micronutrients, especially iron.[9] The cost of distributing iron over large ocean areas is large compared with the expected value of carbon credits.[10] Research in the early 2020s suggested that it could only permanently sequester a small amount of carbon.[11]
^Monastersky, Richard (September 30, 1995). "Iron versus the Greenhouse: Oceanographers cautiously explore a global warming therapy". Science News. 148 (14): 220–222. doi:10.2307/4018225. JSTOR4018225.
^Harrison, Daniel P. (2013). "A method for estimating the cost to sequester carbon dioxide by delivering iron to the ocean". International Journal of Global Warming. 5 (3): 231. doi:10.1504/ijgw.2013.055360.