Possible Ecological Consequences of Iron Fertilization of the Oceans
What is ocean iron fertilization?
Iron is vital for the life of phytoplankton, being crucial for many processes. Weinberg 1989 listed these important processes as �synthesis of DNA, RNA, and chlorophyll; electron transport; oxygen metabolism; and nitrogen fixation�. With all the listed considered, it is apparent that iron needs to be in ample supply, however in many oceans it is not. Iron fertilization was proposed when iron was considered to control phytoplankton production; low concentrations of phytoplankton (containing chlorophyll) would obviously not be able to adequately utilize the nutrients in the ocean by photosynthesis (Martin et al 1988), resulting in a high nutrient, low chlorophyll ecosystem (HNLC). Ocean Iron fertilization (OIF) is therefore used to encourage the growth of phytoplankton, in the form of phytoplankton blooms. The chlorophyll in phytoplankton cells converts light, nutrients and aqueous carbon dioxide (which the ocean has consumed from the atmosphere) oxygen (Bertram 2009). As well as the phytoplankton using CO2 to photosynthesise, Denman, 2008 also indicates that the phytoplankton use (around 30%, Sarmiento and Orr 1991) the dissolved inorganic carbon to form particles of organic carbon in the euphotic zone, in turn a percentage of this organic carbon will be submerged to the sea bed (Bertram 2009) . If the oceans were enhanced with iron phytoplankton concentration would rise, therefore the rate at which the carbon cycle occurred will also increase and in turn a greater amount of particulate organic carbon will sink, hence the use of iron fertilization as a carbon sink, to combat climate change. The process of iron fertilisation is achieved by distributing a controlled concentration of iron solution (SF6) into the surface of selected areas of the HNCL oceans by means of a dosing unit and the depth of the surface water at which the solution will be released will be carried out with a depressor to the depth of around 15m (Boyd et al 2000). Iron fertilization is however a controversial matter, having a variety of both positive and negative consequences on the environment. The environmental impacts of ocean iron fertilization are broad, with mixed opinions; therefore I would like to concentrate on the following ecological consequences. Ocean iron fertilisation can lead to anoxic regions, ultimately creating problems for ocean life forms, including fish. The problem of Anoxia can indirectly lead to the formation of a number of greenhouse gases including; methane, dimethylsulphide,carbon monoxide and the greenhouse gas that I will look at in more depth nitrous oxide (Law 2008). OIF may indirectly lead to more environmental harm if the trace gases released into the atmosphere can cause more damage than the carbon that is being sequestered into the ocean (Law and Ling 2001). may be a consequence of ocean iron fertilization. Referring to my earlier description of the carbon cycle; when iron is used to fertilize the oceans to sink carbon in order to solve the global warming issue; remineralisation occurs during the sinking of carbon.
The environmental impacts of ocean iron fertilization are broad, with mixed opinions; therefore I would like to concentrate on how iron fertilization increases the growth of different phytoplankton; remineralisationthe occurrence of harmful algal blooms, the controversial topic of climate change and
Climate change and global warming are fast becoming an larger environmental problem than was predicted as Denman 2008 explained that �atmospheric CO2 is increasing faster than projected in any of the Intergovernmental Panel on Climate Change (IPCC) emission scenarios �. Being important in current affairs brings great scientific interest and conflicting opinions on the solutions to reduce carbon dioxide emissions and their success. Ocean iron fertilization is one possible solution as it was ultimately developed as a carbon sink to try and combat global warming, with extremely conflicting views; great detrimental consequences on the environment and possibly leading to global warming compared to it being a sufficient means of carbon sequestration and solving global warming.
In 1991 Sarmiento and Orr developed models to show how OIF can cause the ecological result of increasing the carbon intake of the ocean. The models were tested in the Southern Ocean which is a significant example of a HNLC ocean (Moore and Abbott 2000). Sarmiento and Orr�s models proved that in a century, nutrient depletion would result in sequestering around �20% of the total increase of CO2� (Sarmiento and Orr 1991). Sarmiento and Orr developed �models� to represent that phytoplankton (enhanced by ocean iron fertilization) consuming higher rates of the oceans nutrients, will enable the sequestration of carbon dioxide. They proved that if no nutrients were depleted; after they had been for half a century; the sequestered carbon dioxide from that period of time would be removed from the ocean and returned to the atmosphere within a similar time period of 60 years. Sarmiento and Orr acknowledge that further studies need to be carried out with these nutrient depletion experiments, which take into consideration and test a variety of environmental factors, e.g. food chains, wave action, the impact of light intensities. They also recognised the fact that these experiments are simulations and the results may not be completely true when applied to actual situations as Sarmiento and Orr were able to prohibit any nutrient depletion occurring, without any delay necessary. However to make these investigations authentic, Sarmiento and Orr were concerned that the OIF consequence that is ocean anoxia may arise in sub surface regions. Low oxygen area may appear due to nutrient depletion consuming oxygen or as a possible outcome the oxygen returns to the atmosphere (Sarmiento and Orr 1991).
Taking these results into a ccount, Sarmiento and Orr (1991) emphasised that �reduced emissions have a far greater impact on atmospheric CO2 than does nutrient depletion� or when the emissions are �controlled�.
Remineralisation (Bertram 2009 and Denman 2008) and nutrient depletion (Sarmiento and Orr 1991) can initiate deep sea waters to become oxygen depleted, even resulting in anoxic areas. Anoxic areas can form due to remineralisation, because the available mid water oxygen is used by bacteria (even when the oxygen concentration is low) for the following transformation process; in the initial ocean depths, HCO3- and inorganic carbonate will be reformed from the particulate and dissolved carbons during the submerging movement to the deep ocean (Bertram 2009 and Denman 2008). Large scale iron fertilization projects will encourage the remineralisation will occur at a higher rate, hence the consequences will result in anoxic areas of the deep ocean, which will subsequently lead to the �die-offs of marine life, including fish, shellfish, and invertebrates� Powell 2008c. OIF can also result in other ecological consequences from encouragement of remineralisation; for example as remineralisation of the submerging organic carbon occurs, this can lead to a rise in the production of nitrous oxide, N2O as a consequence of nitrification and denitrification (Law and Ling 2001, Law 2008, Denman 2008). As OIF encourages remineralisation, which as shown can lead to anoxic conditions, this will in turn increase the increased production of the nitrous oxide, due do the fact that denitrification occurs in �anoxic sediments and water bodies� (Law 2008).
In 2001, Law and Ling confirmed that the �addition of Fe may have directly stimulated nitrificaiton�, therefore the production of nitrous oxide is an indirect ecological consequence. To demonstrate the influence that a Southern Iron Ocean Release Experiment (SOIREE) had on nitrous oxide production, Law and Ling 2001 set up zones within and outside the SOIREE area. These zones enabled the comparison of how iron fertilisation can influence other ecological processes which may be harmful. Their results indicated that on the whole, in the pycnocline region of the SOIREE zones, the saturation of nitrous oxide was at its absolute limit, with an average of 104.4�2.4% compared to 100.3�1.7% saturation in the same region of non iron fertilised zones (Law and Ling 2001). The nitrous oxide becomes harmful to the atmosphere because, as Law and Ling showed; the nitrous oxide develops in the pycnocline (subsurface ocean depths). This is a problem because sub surface depths hardly become anoxic, and as previously mentioned, denitrification; which is also removes much of the N2O; needs anoxic conditions to occur (Law 2008). Without denitrification occurring, nitrous oxides are emitted into the atmosphere (Denman 2008, Law 2008, Law and Ling 2001). The release of N2O, is an extreme consequence of iron fertilisation as it is