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Ocean Nourishment is a type of geoengineering based on the purposeful introduction of nutrients to the upper ocean (e.g. phosphate) to increase the marine food chain and to sequester carbon dioxide from the atmosphere. Fertilization also creates stratospheric sulfur aerosols and can therefore be used for Solar radiation management. The marine food chain is based on photosynthesis by marine phytoplankton which combine carbon with inorganic nutrients to produce organic matter. The production of organic matter is limited in general by the availability of nutrients, most commonly nitrogen or iron. Numerous experiments have been carried out demonstrating how iron fertilization can increase phytoplankton productivity in the high latitude waters. It is also effective in some lower latitudes. Nitogen appears to be the limiting nutrient in the rest of the ocean and can be supplied by from a number of sources including fixation by cyanobacteria. The efficacy of fixation varies dramatically, with iron fixing more carbon atoms per iron atom than other substances, which is a significant reason for the focus on iron in recent research.
Ocean Nourishment offers the prospect of both reducing the concentration of atmospheric greenhouse gases with the aim of avoiding rapid climate change and at the same time increasing the sustainable fish stocks. It promises to do this by increasing the ocean primary production.
Ocean Nourishment promises to be a way of creating low cost protein in sufficient quantity to supply the needs of the additional two billion people expected to populate the earth before the population stabilizes at values near eight billion. While manipulation of the land ecosystem in support of agriculture for the benefit of humans has long been accepted it is a new concept to enhance the large scale ocean productivity and so creates some apprehension.
This technique can give 0.83W/m2 of globally-averaged negative forcing, which is sufficient to reverse the warming effect of about half the current levels of anthropogenic CO2 emissions. It is notable, however, that CO2 levels will have risen by the time this could be achieved.
An Australian company, Ocean Nourishment Corporation (ONC), plans to sink hundreds of tonnes of urea into the ocean, in order to boost the growth of CO2-absorbing phytoplankton, as a way to combat climate change. In 2007, Sydney-based ONC completed an experiment involving one tonne of nitrogen in the Sulu Sea off the Philippines.
This technique can give 0.38W/m2 of globally-averaged negative forcing, which is sufficient to reverse the warming effect of current levels of around a quarter of anthropogenic CO2 emissions. It is notable, however, that CO2 levels will have risen by the time this could be achieved.
Solar radiation management
As well as carbon sequestration, ocean fertilization can also be used to create sulfate aerosols which reflect sunlight and modify the Earth's albedo, this creating a cooling effect which reduces some of the effects of climate change. Enhancing the natural sulfur cycle in the Southern Ocean ocean by fertilizing a small portion with iron in order to enhance dimethyl sulfide production and cloud reflectivity achieves this. The goal is to slow Antarctic ice from melting and raising sea level. Such techniques also tend to sequester carbon, but in this specific project the enhancement of cloud albedo was both the desired outcome and measured result.
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