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Iron Cycle
The iron cycle (Fe) is the biogeochemical cycle of iron through the atmosphere, hydrosphere, biosphere and lithosphere. While the fourth most abundant in the Earth's crust and many types of soil, it is less common in surface waters. Iron is a key micronutrient in primary productivity, and a limiting nutrient in High-nutrient, low-chlorophyll regions of the ocean. A critical component of the iron cycle is aeolian dust, which is transported from the Earth's land via the atmosphere to the ocean.

Overview
Iron ranges in oxidation states from -2 to +7; however, on Earth it is predominantly in its +2 or +3 redox state. The cycling of iron between its +2 and +3 oxidation states is referred to as the iron cycle. This process can be entirely abiotic or facilitated by microorganisms. Some examples of this include the rusting of iron-bearing metals (in this case Fe2+ is abiotically oxidized to Fe3+) by oxygen, and the abiotic reduction of Fe3+ to Fe2+ by iron-sulfide minerals or the biological cycling of iron-oxidizing microbes.

Iron is an important element on Earth. It is the 4th in abundance in the crust, is an essential element for almost every life form, and is a primary redox-active metal on Earth. Due to the high reactivity of Fe2+ with oxygen and low solubility of Fe3+, iron is a limiting nutrient in most regions of the world. Thus, the iron cycle is intrinsically linked to the cycling of other biologically-important elements.

Oceanic Iron Cycle
The ocean is a critical component of the Earth's climate system, and the iron cycle plays a key role in ocean primary productivity and marine ecosystem function. The largest supply of iron to the oceans is from rivers, where it is suspended as sediment. Other major sources of iron to the ocean include glacial particulates, atmospheric dust transport, and hydrothermal vents. Iron supply is an important factor affecting growth of phytoplankton, the base of marine food web. Uptake of iron by phytoplankton leads to lowest iron concentrations in surface seawater. Remineralization of sinking phytoplankton by zooplankton and bacteria recycles iron and causes higher deep water iron concentrations. Therefore, upwelling zones contain more iron than other areas of the surface ocean.

Terrestrial Iron Cycle
The iron cycle is an important component of the terrestrial ecosystems. The ferrous form of iron, Fe2+, is dominant in the Earth's mantle, core, or deep crust. The ferric form, Fe3+, is more stable in the presence of oxygen gas. Dust is a key component in the Earth's iron cycle. Chemical and biological weathering break down iron-bearing minerals, releasing the nutrient into the atmosphere. Changes in hydrological cycle and vegetative cover impact these patterns and have a large impact on global dust production, with dust deposition estimates ranging between 1000 to 2000 Tg/year. Volcanic eruptions are also a key contributor to the terrestrial iron cycle, releasing iron-rich dust into the atmosphere in either a large burst or in smaller spurts over time. The atmospheric transport of iron-rich dust can impact the ocean concentrations.

Historical Iron Cycle
In the early earth, when atmospheric oxygen levels were 0.001% of those present today, dissolved iron was thought to have been a lot more abundant in the oceans, and thus more bioavailable to microbial life present in that era. At this time, before the onset of oxygenic photosynthesis, primary production may have been dominated by photoferrotrophs, which would obtain energy from sunlight, and use the electrons from Fe+2 to fix carbon.

=Add to an Article= [Summarized steps taken] Sources added to article:

(1) Johnson and Beard, 2005; cited that Fe+2 and Fe+3 are most common oxidation states (plus details added)

(2) Taylor and McClennan, 1985; cited that Iron is the 4th most abundant element in the crust

Links added for iron cycle page: 'oxidation states', 'abiotic', 'electron acceptor'

Pages where iron cycle links were added: 'Rust', 'Iron Oxide', 'Hydrothermal Vent'

= Article Sources: =


 * 1) Archer, D.E.; Johnson, K. (2000). “A model of the iron cycle in the ocean”. Global Biogeochemical Cycles. 14: 269-279. https://doi.org/10.1029/1999GB900053
 * 2) Boyd, P.W.; Ellwood, M. J. (2010). “The biogeochemical cycle of iron in the ocean”. Nature Geoscience. 3: 675-682. http://doi.org/10.1038/NGEO964/
 * 3) Duggen, S.; Olgun, N.; Croot, P.; Hoffman, L.; Dietze, H.; Delmelle, P.; Teschner, C. (2010). “The role of airborne volcanic ash for the surface ocean biogeochemical iron-cycle: a review”. Biogeosciences.  7: 827-844. https://doi.org/10.5194/bg-7-827-2010
 * 4) Homoky, W.B. (2017). “Deep ocean iron balance”. Nature Geoscience. 10: 162-164. https://doi.org/10.1038/ngeo2908
 * 5) Jickells, T.D.; An, Z.S.; Anderson, K.K.; Baker, A.R.; Bergametti, G.; Brooks, N.; Cao, J.J.; Boyd, P.W.; Duce, R.A.; Hunter, K.A.; Kawahata, H.; Kubilay, N.; LaRoche, J.; Liss, P.S.; Mahowald, N.; Prospero, J.M.; Ridgwell, A.J.; Tegen, I.; Torres, R. (2005). “Global Iron Connections between Desert Dust, Ocean Biogeochemistry, and Climate”. Science. 308: 67-71. http://doi.org/10.1126/science.1105959
 * 6) Johnson, Clark M.; Beard, Brian L. (2005). “Biogeochemical cycling of Iron Isotopes”. Science. 309: 1025-1027. http://doi.org/10.1126/science.1112552
 * 7) Kendall, Brian; Anbar, Ariel D.; Kappler, Andreas; Konhauser, Kurt O. (2012). “The Global Iron Cycle”. Fundamentals of Geobiology. 1: 65-92.https://doi.org/10.1002/9781118280874.ch6
 * 8) Mahowald, N.M.; Baker, A.R.; Bergametti, G.; Brooks, N.; Duce, R.A.; Jickells, T.D.; Kubilay, N.; Prospero, J.M.; Tegen, I. (2005). “Atmospheric global dust cycle and iron inputs to the ocean”. Global Biogeochemical Cycles. 19: 1-15. http://doi.org/10.1029/2004GB002402
 * 9) Muller, D. B.; Wang, T.; Duval, B.; Graedel, T.E. (2006). “Exploring the engine of anthropogenic iron cycles”. Proceedings of the National Academy of Sciences. 103 (44): 16111-16116. http://doi.org/10.1073.pnas.0603375103
 * 10) Raiswell, R. (2006). “Towards a global highly reactive iron cycle”. Journal of Geochemical Exploration. 88: 436-439. http://doi.org/10.1017/j.gexplo.2005.08.098
 * 11) Tagliabur, A.; Bowie, A.R.; Boyd, P.W.; Buck, K.N.; Johnson, K.S.; Salto, M.A. (2017). “The integral role of iron in ocean biogeochemistry”. Nature. 543: 51-59. http://doi.org/10.1038/nature21058
 * 12) Wang, T.; Buller, D.B.; Graedel T.E.; (2007). ”Forging the Anthropogenic Iron Cycle”. Environmental Science & Technology. 41: 5120-5129. http://doi.org/10.1021/es062761t

= Article Evaluation: = Content: The content of the iron cycle Wikipedia page, in its current state, has a lot of room for improvement. The overview has a few useful points but doesn’t extrapolate enough on those points to truly help someone understand the cycle. For example, it mentions the range of oxidation states of iron, but does nothing to define oxidation states or explain why they matter in terms of the iron cycle. There is not nearly enough information, and the only sections are “Overview” and “History of Iron Cycling on Earth”. Examples for needed edits include adding to the history section, or creating further sections such as ‘ocean’ and ‘terrestrial’, a focus on human/animal influences and impacts. The Overview section needs improvement and further information, including why the iron cycle is important and improved explanations of the existing facts provided.

Tone: The tone of the article is appropriately scientific, but some of the sentences are written kind of short, and the words are not defined very well. That being said, the tone is not taking any one side (it is appropriately neutral) and it doesn’t give viewpoints that are the authors. It is a pretty appropriate tone.

Sources: Currently there are only three references, two of which are correctly cited. Both correctly cited links work and are peer reviewed sources. In one point in the article, in the “history of iron cycling on Earth” section, it even says ‘citation needed’ in the published Wikipedia article. There should be many more sources and links throughout the article both connecting to other Wikipedia pages (for example, ‘oxidation state’ is an extremely detailed Wikipedia page that would be a very useful link to include) as well as more science web pages and peer-reviewed citations.

About Talk Page: So far it looks like the Iron Cycle has been flagged by several geological-oriented organizations (WikiProject Geology and WikiProject Soil) as low-level or in need of edits, but has also been flagged as low importance. There has been no activity or discussions on the talk page, however, indicating low interest and very little other edits that have been done over time.