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Approximately 50% of Earth’s oxygen is produced in the Ocean (Field et al., 1998), mostly by phytoplankton.
Phytoplankton are unicellular (microscopic) marine algae which carries out photosynthesis thanks to chlorophyll. They are living at the ocean surface and their distribution varies depending on the geography, seasonality, sunlight supply, nutrient availability, water temperature, salinity, and Ocean currents. They are found almost everywhere at the ocean surface, where there is sunlight (Marilaure Grégoire et al., 2023).
The photosynthesis consumes carbon dioxyde and produces oxygen, as shown in the following equation:
Sunlight Energy + Water + Carbon Dioxide → Organic matter + Oxygen
A part of this oxygen then goes in the atmosphere through the ocean-atmosphere interface. It is thanks to cyanobacteria living in the very first ocean after the Earth formation performing photosynthesis that we do have oxygen in the atmosphere! At that time, it was not any plant on land.
In spring, when the phytoplankton blooms, it can be visible from satellites view! Scientists use satellites images to estimate the phytoplankton productivity by quantifying the chlorophyll α and colour observations (Bellacicco et al., 2020; Richardson and Bendtsen, 2017). It is used to track their photosynthesis activity but also the phytoplankton populations. It is very imortant as they are playing a fundamental role in the climate regulation and are the base of the food web.
Satellite picture of a phytoplankton bloom in the Barents Sea.
Credit:
European space agency (ESA), licence CC BY-SA 3.0 IGO
https://www.esa.int/ESA_Multimedia/Images/2011/08/Phytoplankton_bloom_captured_by_Envisat
Photosynthesis might be making an important contribution to water column oxygenation (Richardson and Bendtsen, 2017). Studies found that an ocean surface warming may lead to a decrease of phytoplankton productivity and so, a deoxygenation of the surface ocean, causing an increase of the stratification of the water column (Bopp et al., 2013; Hoegh-Guldberg and Bruno, 2010; p359, 714 Intergovernmental Panel On Climate Change, 2021; Marilaure Grégoire et al., 2023). Furthermore, Richardson et al. (2017) mention that changes initiated by a warmer ocean (also see Intergovernmental Panel On Climate Change, 2021, p75) may have implication for the oxygen production and export.
Bibliograhy
Bellacicco, M., Pitarch, J., Organelli, E., Martinez-Vicente, V., Volpe, G., and Marullo, S.: Improving the Retrieval of Carbon-Based Phytoplankton Biomass from Satellite Ocean Colour Observations, Remote Sensing, 12, 3640, https://doi.org/10.3390/rs12213640, 2020.
Bopp, L., Resplandy, L., Orr, J. C., Doney, S. C., Dunne, J. P., Gehlen, M., Halloran, P., Heinze, C., Ilyina, T., Séférian, R., Tjiputra, J., and Vichi, M.: Multiple stressors of ocean ecosystems in the 21st century: projections with CMIP5 models, Biogeosciences, 10, 6225–6245, https://doi.org/10.5194/bg-10-6225-2013, 2013.
Field, C. B., Behrenfeld, M. J., Randerson, J. T., and Falkowski, P.: Primary Production of the Biosphere: Integrating Terrestrial and Oceanic Components, Science, 281, 237–240, https://doi.org/10.1126/science.281.5374.237, 1998.
Hoegh-Guldberg, O. and Bruno, J. F.: The Impact of Climate Change on the World’s Marine Ecosystems, Science, 328, 1523–1528, https://doi.org/10.1126/science.1189930, 2010.
Intergovernmental Panel On Climate Change: Climate Change 2021 – The Physical Science Basis: Working Group I Contribution to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, 1st ed., Cambridge University Press, https://doi.org/10.1017/9781009157896, 2021.
Marilaure Grégoire, Oschlies, A., Canfield, D. E., Castro, C., Ciglenečki, I., Croot, P., Salin, K., Schneider, B., Serret, P., Slomp, C., Tesi, T., and Yucel, M.: Ocean Oxygen: the role of the Ocean in the oxygen we breathe and the threat of deoxygenation, Zenodo, https://doi.org/10.5281/ZENODO.7941157, 2023.
Richardson, K. and Bendtsen, J.: Photosynthetic oxygen production in a warmer ocean: the Sargasso Sea as a case study, Phil. Trans. R. Soc. A., 375, 20160329, https://doi.org/10.1098/rsta.2016.0329, 2017.
September 2024
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