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Iron is often a unique missing nutrient whose scarcity limits the growth and reproduction of life

In many parts of the oceans, iron is a unique missing nutrient whose scarcity limits the growth and reproduction of life at every level of the food chain12345. Iron plays a crucial role in various biochemical processes necessary for the growth and proliferation of marine life, particularly phytoplankton. Here are the key reasons why iron is so important and often the limiting nutrient in marine ecosystems:

Essential Role in Biochemical Processes​

  1. Photosynthesis: Iron is a critical component of the chlorophyll molecule and is involved in the electron transport chain during photosynthesis67. It is necessary for the formation of the enzyme complexes that convert light energy into chemical energy.

  2. Nitrogen Fixation: Certain phytoplankton, such as cyanobacteria, can fix atmospheric nitrogen into a form usable by other organisms. This process requires the enzyme nitrogenase, which contains iron89.

Why Iron is Often the Limiting Nutrient​

  1. Low Solubility: Iron is relatively insoluble in seawater. Most of the iron in the ocean is in a form that is not easily accessible to organisms. This low solubility means that even if there is iron present, it might not be in a bioavailable form101112.

  2. Sources of Iron: The main sources of iron to the ocean are dust deposition from the atmosphere, volcanic eruptions, and upwelling of deep waters. In many parts of the ocean, these sources are limited, leading to regions where iron is scarce1314.

Iron Limitation and Marine Ecosystems​

  1. High-Nutrient, Low-Chlorophyll (HNLC) Regions: In areas like the Southern Ocean, the equatorial Pacific, and parts of the North Pacific, there are plenty of macronutrients (like nitrogen and phosphorus) but very low concentrations of iron. In these regions, phytoplankton growth is limited primarily by the availability of iron[^15][^16][^17].

Sources:​

Footnotes​

  1. Galbraith, E. D., Le Mézo, P., Hernandez, G. S., Bianchi, D., & Kroodsma, D. A. (2019). Growth limitation of marine fish by low iron availability in the open ocean. Frontiers in Marine Science, 6. https://doi.org/10.3389/fmars.2019.00509 ↩

  2. Ussher, S. J., Achterberg, E. P., & Worsfold, P. J. (2004). Marine biogeochemistry of iron. Environmental Chemistry, 1(2), 67-67. https://doi.org/10.1071/en04053 ↩

  3. Schoffman, H., Lis, H., Shaked, Y., & Keren, N. (2016). Iron–nutrient interactions within phytoplankton. Frontiers in Plant Science, 7. https://doi.org/10.3389/fpls.2016.01223 ↩

  4. Martin, J. H. (1992). Iron as a limiting factor in oceanic productivity. In Primary productivity and biogeochemical cycles in the sea (pp. 123-137). Springer. https://doi.org/10.1007/978-1-4899-0762-2_8 ↩

  5. Moore, C. M., Mills, M. M., Arrigo, K. R., Berman-Frank, I., Bopp, L., Boyd, P. W., Galbraith, E. D., Geider, R. J., Guieu, C., Jaccard, S. L., Jickells, T., LaRoche, J., Lenton, T. M., Mahowald, N. M., Marañón, E., Marinov, I., Moore, J. K., Nakatsuka, T., Oschlies, A., Saito, M. A., Thingstad, T. F., Tsuda, A., & Ulloa, O. (2013). Processes and patterns of oceanic nutrient limitation. Nature Geoscience, 6(9), 701-710. https://doi.org/10.1038/ngeo1765 ↩

  6. NCBI. (2023, February). Photosynthesis. NCBI. https://www.ncbi.nlm.nih.gov/books/NBK9861/ ↩

  7. Alberts, B., Johnson, A. D., Lewis, J., Raff, M., Roberts, K., & Walter, P. (2007). Molecular biology of the cell. Taylor & Francis. https://doi.org/10.1201/9780203833445 ↩

  8. Santi, C., Bogusz, D., & Franche, C. (2013). Biological nitrogen fixation in non-legume plants. Annals of Botany, 111(5), 743-767. https://doi.org/10.1093/aob/mct048 ↩

  9. Newton, W. E. (2007). Physiology, biochemistry, and molecular biology of nitrogen fixation. In Biological nitrogen fixation (pp. 109-129). Elsevier. https://doi.org/10.1016/b978-044452857-5.50009-6 ↩

  10. Elrod, V. A., Berelson, W. M., Coale, K. H., & Johnson, K. S. (2004). The flux of iron from continental shelf sediments: A missing source for global budgets. Geophysical Research Letters, 31(12). https://doi.org/10.1029/2004gl020216 ↩

  11. Liu, X., & Millero, F. J. (2023, November). The solubility of iron in seawater. Marine Chemistry. https://www.sciencedirect.com/science/article/pii/S0304420301000743 ↩

  12. Millero, F. J. (2023, December). Solubility of Fe(III) in seawater. Earth and Planetary Science Letters. https://www.sciencedirect.com/science/article/pii/S0012821X97001799 ↩

  13. Mahowald, N. M., Baker, A. R., Bergametti, G., Brooks, N., Duce, R. A., Jickells, T., Kubilay, N., Prospero, J. M., & Tegen, I. (2005). Atmospheric global dust cycle and iron inputs to the ocean. Global Biogeochemical Cycles, 19(4). https://doi.org/10.1029/2004gb002402 ↩

  14. Hettiarachchi, E., Hurab, O., & Rubasinghege, G. (2018). Atmospheric processing and iron mobilization of ilmenite: Iron-containing ternary oxide in mineral dust aerosol. Journal of Physical Chemistry A, 122(5), 1291-1302. https://doi.org/ ↩