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Denser Concentrations of Life in the Ocean Are Due to Nutrients

The primary reason for denser concentrations of life in some parts of the ocean is access to nutrients12. Nutrients like nitrogen, phosphorus, and iron are essential for the growth and proliferation of marine organisms, particularly primary producers such as phytoplankton345. These nutrients often limit productivity in many parts of the ocean, creating areas of low and high biological activity depending on their availability637.

Nutrient Availability and Phytoplankton Growth​

Phytoplankton, the foundation of marine food webs, require nutrients to perform photosynthesis and grow8. Regions with upwelling, where deep, nutrient-rich waters are brought to the surface, typically exhibit higher concentrations of phytoplankton. This phenomenon is evident in areas such as the eastern boundaries of major oceans (e.g., the coasts of Peru and California) where upwelling leads to high productivity and dense marine life concentrations9.

Iron's Role in Marine Ecosystems​

Iron is a critical micronutrient for phytoplankton1011. In high-nutrient, low-chlorophyll (HNLC) regions like the Southern Ocean, equatorial Pacific, and parts of the North Pacific, iron limitation restricts phytoplankton growth despite the presence of other nutrients. When iron is introduced into these areas, either naturally or through artificial fertilization experiments, there is a notable increase in phytoplankton biomass, demonstrating the pivotal role of iron in controlling productivity and, consequently, the density of marine life8.

Nutrient Cycling and Zooplankton​

Zooplankton, which feed on phytoplankton, thrive in nutrient-rich environments. Increased phytoplankton biomass supports larger populations of zooplankton, which in turn serve as food for higher trophic levels, including fish, birds, and marine mammals. This cascading effect emphasizes how nutrient availability at the base of the food web affects the entire marine ecosystem[^12][^13].

Case Studies of High Nutrient Areas​

  1. Coastal Upwelling Zones: These regions are known for their nutrient influx from deeper waters, leading to high biological productivity. For instance, the Benguela and Humboldt Current systems are among the most productive marine ecosystems globally due to persistent upwelling9.

  2. River Plumes: Areas where large rivers discharge into the ocean, such as the Amazon and Mississippi River deltas, are nutrient-rich and support dense concentrations of marine life due to the influx of terrestrial nutrients[^14][^15].

Sources:​

Footnotes​

  1. Karl, D. M. (2002). Nutrient dynamics in the deep blue sea. Trends in Microbiology, 10(9), 410-418. https://doi.org/10.1016/s0966-842x(02)02430-7 ↩

  2. Rivkin, R. B., & Legendre, L. (2002). Roles of food web and heterotrophic microbial processes in upper ocean biogeochemistry: Global patterns and processes. Marine Ecology Progress Series, 17(2), 151-159. https://doi.org/10.1046/j.1440-1703.2002.00475.x ↩

  3. 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 ↩ ↩2

  4. NOAA. (2023, February). Nutrient biogeochemistry. NOAA. https://www.aoml.noaa.gov/ocd/ocdweb/nutrients.html ↩

  5. Hedges, J. I., Baldock, J., Gélinas, Y., Lee, C., Peterson, M., & Wakeham, S. G. (2002). The biochemical and elemental compositions of marine plankton: A NMR perspective. Marine Chemistry, 78(1), 47-63. https://doi.org/10.1016/s0304-4203(02)00009-9 ↩

  6. Raven, J. A., Brown, K. C., Mackay, M., Beardall, J., Giordano, M., Granum, E., Leegood, R. C., Kilminster, K., Walker, D., & Lagares, A. (2010). Iron, nitrogen, phosphorus and zinc cycling and consequences for primary productivity in the oceans. In Oceanography (pp. 247-272). Cambridge University Press. https://doi.org/10.1017/cbo9780511754852.013 ↩

  7. Bristow, L. A., Mohr, W., Ahmerkamp, S., & Kuypers, M. M. M. (2017). Nutrients that limit growth in the ocean. Current Biology, 27(11), R474-R478. https://doi.org/10.1016/j.cub.2017.03.030 ↩

  8. Browning, T. J., & Moore, C. M. (2023). Global analysis of ocean phytoplankton nutrient limitation reveals high prevalence of co-limitation. Nature Communications, 14(1). https://doi.org/10.1038/s41467-023-40774-0 ↩ ↩2

  9. Umasangaji, H., & Ramili, Y. (2021). Mini review: Characteristics of upwelling in several coastal areas in the world. IOP Conference Series: Earth and Environmental Science, 890(1), 012004. https://doi.org/10.1088/1755-1315/890/1/012004 ↩ ↩2

  10. Schoffman, H., Lis, H., Shaked, Y., & Keren, N. (2016). Iron–nutrient interactions within phytoplankton. Frontiers in Plant Science, 7, 1223. https://doi.org/10.3389/fpls.2016.01223 ↩

  11. Johnson, K. S., Chávez, F. P., Elrod, V. A., Fitzwater, S. E., Pennington, J. T., Buck, K. R., & Walz, P. M. (2001). The annual cycle of iron and the biological response in central California coastal waters. Geophysical Research Letters, 28(7), 1247-1250. https://doi.org/10.1029/2000GL012433 ↩