Why is it a problem when the ocean acidifies through the absorption of CO2?

Why is it a problem when the ocean acidifies through the absorption of CO2?

Year after year, the ocean absorbs about a quarter of man-made carbon dioxide (#1). In doing so, it reduces the additional greenhouse effect, but this comes at a high price. This is because the carbon dioxide reacts with seawater to form carbonic acid, which gradually acidifies the sea (#2). A phenomenon known as ocean acidification.

Since the beginning of industrialization, the acidity of seawater has increased by 30%. And this in turn has significant consequences for marine life. Especially for all those organisms that build their shells and skeletons from calcium carbonate (#3). This not only applies to corals, mussels, snails, sea urchins and sea stars, also many microorganisms in the plankton form their shells from calcium carbonate. Ocean acidification gradually consumes the carbonate dissolved in seawater, one of the building materials for calcium carbonate. Less carbonate means that the formation of calcium carbonate becomes more and more costly (#4).

Many calcifiers will no longer be able to maintain their niche in the ecosystem as ocean acidification progresses (#5). This not only reduces biodiversity, but also changes marine ecosystem functioning – and ultimately also the vital services from the ocean we humans rely on (#6).

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#1 Friedlingstein, P., Jones, M. W., O’Sullivan, M., Andrew, R. M., Hauck, J., Peters, G. P., Peters, W., Pongratz, J., Sitch, S., Le Quéré, C., Bakker, D. C. E., Canadell, J. G., Ciais, P., Jackson, R. B., Anthoni, P., Barbero, L., Bastos, A., Bastrikov, V., Becker, M., Bopp, L., Buitenhuis, E., Chandra, N., Chevallier, F., Chini, L. P., Currie, K. I., Feely, R. A., Gehlen, M., Gilfillan, D., Gkritzalis, T., Goll, D. S., Gruber, N., Gutekunst, S., Harris, I., Haverd, V., Houghton, R. A., Hurtt, G., Ilyina, T., Jain, A. K., Joetzjer, E., Kaplan, J. O., Kato, E., Klein Goldewijk, K., Korsbakken, J. I., Landschützer, P., Lauvset, S. K., Lefèvre, N., Lenton, A., Lienert, S., Lombardozzi, D., Marland, G., McGuire, P. C., Melton, J. R., Metzl, N., Munro, D. R., Nabel, J. E. M. S., Nakaoka, S.-I., Neill, C., Omar, A. M., Ono, T., Peregon, A., Pierrot, D., Poulter, B., Rehder, G., Resplandy, L., Robertson, E., Rödenbeck, C., Séférian, R., Schwinger, J., Smith, N., Tans, P. P., Tian, H., Tilbrook, B., Tubiello, F. N., van der Werf, G. R., Wiltshire, A. J., and Zaehle, S.: Global Carbon Budget 2019, Earth Syst. Sci. Data, 11, 1783–1838, https://doi.org/10.5194/essd-11-1783-2019, 2019.

#2 Raven, J., Caldeira, K., Elderfield, H., Hoegh-Guldberg, O., Liss, P., Riebesell, U., Shepherd, J., Turley, C. and Watson, A. (2005) Ocean acidification due to increasing atmospheric carbon dioxide. Royal Society Report, Policy Doc. 12/05, London.

#3 Wittmann, A. and Pörtner, H.-O. (2013) Sensitivities of extant animal taxa to ocean acidification. Nature Climate Change 3(11), 995-1001

#4 Barry, J.P., Widdicombe, S. and Hall-Spencer, J. (2011) Effects of Ocean Acidification on Marine Biodiversity and Ecosystem Function. In: Ocean Acidification, Oxford, pp.192-209

#5 Riebesell, U., Bach, L. T., Bellerby, R. G. J., Bermudez, R., Boxhammer, T., Czerny, J., Larsen, A., Ludwig, A., Schulz,, K. G. (2017) Ocean acidification impairs competitive fitness of a predominant pelagic calcifier. Nature Geoscience 10, 19-24, doi:10.1038/ngeo2854

#6 Nagelkerken, I. and  Connell, S.D. (2015) Global alteration of ocean ecosystem functioning due to increasing human CO2 emissions. Proceedings of the National Academy of Sciences of the United States of America 112 (43), 13272-13277

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