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Iron is vital for the life of phytoplankton, being crucial for many processes. Weinberg 1989 listed these important processes as ï¿½synthesis of DNA, RNA, and chlorophyll; electron transport; oxygen metabolism; and nitrogen fixationï¿½. 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 (Martin 1990); low concentrations of phytoplankton (containing chlorophyll) would obviously not be able to adequately utilize the nutrients in the ocean by photosynthesis (Martin et al 1989), 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 (Pollard et al 2009). The chlorophyll in phytoplankton cells converts light, nutrients and aqueous carbon dioxide (which the ocean has consumed from the atmosphere) into oxygen (Bertram 2010). As well as the phytoplankton using CO2 to photosynthesise, Denman, 2008 also indicates that the phytoplankton use some of the dissolved inorganic carbon (around 30% according to Sarmiento and Orr 1991) 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 2010) . If the oceans were enhanced with iron, the 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 (Southern Ocean, Equatorial Pacific Ocean and Subarctic Pacific Ocean (Fitzwater et al 1996)) by means of a dosing unit and the depth of the surface water at which the solution will be released will be controlled by 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 ecological consequences. The environmental impacts of ocean iron fertilization are widespread with many direct consequences, leading to indirect, possibly more harmful problems. Therefore, I would like to concentrate on the following ecological consequences. OIF results in the increase of various species of phytoplankton, which can in turn lead to harmful blooms, with ecological consequences (Martin et al, 1989, Malando et al 2002, Bertram 2010). Ocean iron fertilisation can lead to anoxic regions, ultimately creating problems for ocean life forms, including fish (Powell 2008c). 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 indirectly causing greenhouse gases may lead to more environmental harm if these trace gases released into the atmosphere can cause more damage than the carbon that is being sequestered into the ocean (Law and Ling 2001). More damage may be caused as some trace gases have a higher Global Warming Potential (GWP) than carbon, as Forster (2007) showed that nitrous oxidesï¿½ GWP was 310 times higher (Law 2008 and Bertram 2010). Referring to my earlier description of the carbon cycle; when iron is added to the oceans to sink carbon in order to solve the global warming issue; remineralisation and nutrient depletion occurs during the sinking of carbon (Bertram 2010).
Climate change and global warming are fast becoming an larger environmental problem than was predicted as Denman 2008 explained that ï¿½atmospheric CO2 is increasing faster than projected in any of the Intergovernmental Panel on Climate Change (IPCC) emission scenarios ï¿½. Being important in current affairs brings great scientific interest and conflicting opinions on the solutions to reduce carbon dioxide emissions and their success. To combat this issue, experiments have been set up to consider the effect that iron addition has on phytoplankton numbers, Martin et al (1989) set up model experiments based on just that. Martin et al (1989) compared the phytoplankton growth rates at three different sites under iron enhanced conditions and those without extra iron added. In 2 of these sites under non enhanced conditions, coccolithophorids thrived. However, with the addition of iron, it is the concentration of diatoms of Nitzschia species, which increase greatest. The third site illustrated that the Nitzschia speciesï¿½ growth rates increased in conditions both with and without the addition of iron. Martin et al were able to conclude that iron may increase the oceans diatom production. Fitzwater et al (1996) similarly proved that diatoms were the phytoplankton to increase in growth rates through ocean iron fertilisation, whilst detecting the pigment growth. To quote Fitzwater et al (1996), ï¿½the pigments, other than chlorophyll a, that showed the most consistent and substantial increases in response to Fe additions were chlorophyll c, fucoxanthin, diadinoxanthin and beta-carotene, which are the main pigments in diatomsï¿½ emphasising that the growth rates of diatoms were aided by OIF. Increasing phytoplankton numbers will also have an effect on the diets of other marine life for instance, copepods (Kruse et al, 2009). Increased phytoplankton, especially diatoms, may seem like a beneficial consequence as increased phytoplankton indicates increased food availability for marine animals including fish, however this may not be the case, as the increase in diatoms may actually be lethal to the ecosystem (Powell 2008c).
The diatom blooms that have been encouraged by OIF may actually be damaging, as they may contain large volumes of the diatom potentially harmful Pseudo-nitzchia, which are from the same family as the Nitzschia spp. described in the Martin et al (1989) investigation. Versions of these Pseudo-nitzchia diatoms, including P.australis and P.multiseries can generate Domoic acid (Maldonado et al, 2002). As these blooms are encouraged by iron fertilisation, once established, they also require iron in abundance to grow and produce the dangerous Domoic acid, as Maldonando et al, 2007 established. Hence, OIF can result in the potential rise of P.australis and P.multiseries, and also aid them to generate and produce higher volumes of Domoic acid through the intake of iron (Maldonando et al, 2007). Maldonando et al, 2007 found that when iron was in plentiful supply, the speed at which the 2 diatoms developed at was much higher. The experiment also displayed that ï¿½intracellular DA concentrations and production (accumulation) rates were two times higher in Fe sufficient-cells than in Fe deficient cellsï¿½ (Maldonado et al 2002) which shows the potential hazard if this acid was discharged, as the result can cause shellfish poisoning and memory loss.
Ocean iron fertilization could help resolve the problem of climate change as, due the initial phytoplankton increase, the oceans potential as a carbon sink would increase as increase of phytoplankton numbers will result in a higher consumption rate of carbon dioxide (Bertram, 2010). 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 Orrï¿½s models proved that in a century, nutrient depletion would result in sequestering around ï¿½20% of the total increase of CO2ï¿½ (Sarmiento and Orr 1991). Sarmiento and Orr developed ï¿½modelsï¿½ 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).
Remineralisation (Bertram 2010 and Denman 2008) and nutrient depletion (Sarmiento and Orr 1991) can also 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 2010 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 ï¿½die-offs of marine life, including fish, shellfish, and invertebratesï¿½ Powell 2008c. OIF can also result in other ecological consequences from encouragement of remineralisation; for example as the 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 ï¿½anoxic sediments and water bodiesï¿½ (Law 2008).
In 2001, Law and Ling confirmed that the ï¿½addition of Fe may have directly stimulated nitrificaitonï¿½, 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 104.4ï¿½2.4% compared to 100.3ï¿½1.7% 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 such a powerful greenhouse gas. Therefore whilst trying to prevent global warming by sequestering CO2, iron fertilization may actually be making the problem worse through the discharge of nitrous oxide (Law 2008, Bertram 2010).
As presented, there are a great number of ecological consequences of ocean iron fertilization. The consequences of OIF are superficially positive as the increase in phytoplankton numbers will; provide a greater food source for fish whose numbers may be depleting (Bertram 2010) and other ocean life forms, as well as resulting in more carbon dioxide being removed from the atmosphere by creating a carbon sink, this will contribute to solving our global warming situation. However, taking these positives into account, when the knock on effects of initially increasing the phytoplankton growth rates are considered, the production of harmful phytoplankton; anoxic areas occurring which may in turn will lead to the production of greenhouse gases (nitrous oxide) which may be more harmful than carbon dioxide. The harmful consequences, although indirect, seem to