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Argument against ocean fertilization
Ocean fertilization has been proposed as a means to combat climate change due to the increased anthropogenic CO2. Phytoplankton is crucial in the carbon cycle as CO2 is fixed by phytoplankton, this facilitates the removal of CO2 from the surface waters, however if this CO2 is not carried to deeper water it will ultimately lead to CO2 re-entering the atmosphere due to respiration (Boyd et el 2003). The reduction of C02 on surface waters, will lead to CO2 removal from the atmosphere as this gradient is maintained by the biological pump. If an effective way to exploit this could be determined it would ultimately be effective, yet ocean fertilization is no solution. There is very little experimental support; the disadvantages outweigh the benefits.
One of the proposals for ocean fertilization is to supply the ocean with nutrient cocktails made on land. Production of nutrient cocktails and its piping to the ocean from land will be an expensive process. All cost need to be considered such as the phosphorus mining, the energetic cost and the carbon footprint produced, which may exceed the sequestration which may occur is response to ocean fertilization. Increased nutrients may increase phytoplankton, if there are no other limiting factors such as Iron essential in utilization of macronutrient. Increased nutrients may have no effect due to the mismatch in timing between the amount of nutrients added and the amount of CO2 absorbed by the ocean, preventing sequestration of CO2 from the atmosphere. Despite an increase in phytoplankton the CO2 absorbed from atmosphere is slow thus sequestration may not be increased. Another proposal concerning macronutrient addition was the extraction of nitrogen gas from the atmosphere and its conversion to ammonia to be added to the ocean. The proposal makes the assumption that phosphate is always in excess, this is not so and varies in different regions of the ocean, thus not a sufficient proposal for ocean fertilization as it is unlikely to increase carbon sequestration. (Lampitt et el 2008)
Another proposition was to use local wave power to pump deep nutrient rich water from depth of several hundred meters to surface waters.(Lampitt et el 2008) Deep waters are rich in carbon dioxide which will be released back to environment thus ultimately more likely to affect global warming by the greenhouse effect rather then counter act it.
Iron fertilization is a key area of research, it has been suggested that the addition of iron to high nutrient low chlorophyll regions will help increase CO2 sequestration. There is much evidence that the addition of iron both naturally and artificially is responsible for the increase in phytoplankton. Yet this is not enough to suggest sequestration will be increased. The proposed iron fertilization will have little effect as iron obtained from dust and rivers is much greater then any addition that is yob r made. Iron supplied may not be bio available and may also be easily lost due to its high reactivity, regular addition will be required, thus not a long-term solution. Formation of phytoplankton blooms may cause an imbalance in the ocean as nutrient may be redistributed as a result. Increased phytoplankton may be countered by the increased grazing. 12 experiments have demonstrated that iron addition to HNLC regions leads to phytoplankton blooms however have failed to look at the effects on Carbon dioxide removed the from atmosphere. (Cullen et el 2001) Iron fertilization induces an increased mineralisation of carbon and nitrates this leads to increased N2O emission which will ultimately counter act any benefit, as N2O is a mush stronger green house gas (Jin et el 2003). Therefore there is very little support for it improving climate change and does not look like an effective solution in the long-term.
Experiment in 2004 in which iron sulphate was added to sub Antarctic pacific provided no evidence of carbon sequestration, this was accounted for by other limitations such as light and the level of silicates (Strong et el 2008). Models fail to demonstrate all feature of the iron cycle thus difficult to assess or provide support for iron fertilization there. (Watson et el 2008)
A possible consequence of ocean fertilization is coastal eutrophication due to increased nitrates and phosphates leading to reduced dissolved oxygen levels in waters, due to high algal bloom formation. There is a concomitant reduction in diversity as well as high mortality which may increase sequestration, yet will have negative effects on fisheries, which around 1.3 billion people rely on (Lampitt et el 2008). Deep ocean hypoxia can lead to release of harmful greenhouse gases such as methane (Jin et el 2004). Harmful algal blooms can cause harm to humans via paralytic shell fish poisoning.
The ocean is essential in maintaining natural cycles and withholds many biological communities; the addition of nutrient causes an imbalance which in turn affects ecosystems. (Strong et el 2009)Iron fertilization will cause an alteration in the base of food webs as it favours the production of phytoplankton this will affect the community structures in the ocean. Biological communities change in the euphotic zone and fisheries effected which approximately 1.3 billion people rely upon.
Nutrient redistribution can occur globally in order to reach a balance of macronutrient,(Lampitt et el 2008) thus fertilization will not lead to sequestration or increased productivity but to disadvantageous effects on fisheries due to nutrient robbing in areas where there are being bred.
In conclusion ocean fertilization as a means to mitigate climate change will be ineffective as anthropogenic CO2 is increasing at a rate which sequestration cannot compete with. The costs of ocean fertilization out weigh the benefits, we require a long-term solution which it is failing to provide and the lack of experimental support makes it difficult to consider ocean fertilization as a solution to mitigate climate change.
Buesseler.K.O and Boyd.P.W (2003) Will Ocean Fertilization Work? Science 300: 67-68
Cullen.J.J Chisholm.S.W, Falkowski.P.G, (2001) Dis-Crediting Ocean Fertilization Science 294:309-310
Lampitt.R.S et el (2008) Ocean fertilization: a potential means of geoengineering? Phil.Trans.R.Soc.A 366: 3919-3945
Watson.A.J, Boyd.P.W, TurnerS.M, Jickells.T.D, Liss.P.S(2008) Designing the next generation of ocean iron fertilization experiments Mar Ecol Prog Ser 364: 303-309
Jin.X and Gruber.N (2003) Offsetting the radiative benefit of ocean iron fertilization by enhancing N2O emissions Geophys. Res. Lett., 30(24): OCE 3:1-3:4
Strong A.L, Cullen.J.J Chisholm.S.W (2009) Ocean Fertilization Science, Policy, and Commerce Oceanography 22(3):236-261