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What is acidification

Ocean Acidification (OA) is a pressing environmental concern that affects the health of our oceans and the people who use them.
Overview
Increased atmospheric carbon dioxide (CO₂) levels, caused by the burning of fossil fuels and deforestation, is the primary driver of a process termed ocean acidification, where the addition of CO₂ to the surface ocean acts to increase seawater acidity and lower pH.

Why It Matters

Carbon dioxide gas dissolves so readily in seawater that approximately one quarter of human caused CO₂ emissions become sequestered in the ocean. Once in the ocean, CO₂ combines with water to form a weak acid, resulting in a change in the chemistry of the sea.

The Chemistry of Ocean Acidification

The other major change in seawater chemistry involves CO₂-driven changes in the solubility of calcium carbonate minerals (CaCO₃) used by many marine plants and animals to build their shells and skeletons.rnrnThe solubility of CaCO₃ minerals depend on the amount of dissolved carbonate ions in seawater.rnrnMore CO₂ and lower pH reduces the concentration of carbonate ions, making it more difficult for many organisms to make shell material.

Ocean CO₂ and pH from NOAA: Correlation between rising levels of CO2 in the atmosphere at Mauna Loa with rising CO₂ levels in ocean at Station Aloha. As the CO₂ increases, the pH decreases; indicating increasing acidificication.

Stressors

Ocean Acidification Is One of Many Human Impacts Changing Marine Ecosystems

Other human-influenced stressors, such as nutrient-induced oxygen deficiencies (hypoxia) and rising water temperatures, co-occur with normal daily and seasonal marine cycles like salinity , primary productivity, and tides. These interactions, influenced by both natural processes and changes in climate, resulting in complex and often unpredictable ecological responses.

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Infographic: Common Stressors to Individual Organisms & Ecosystems

The Interaction of Multiple Stressors

Multiple stressors interact and affect individual organisms and entire ecosystems in a complex way. The impact of co-occurring stressors can be additive or synergistic (meaning that the combined effect is greater than the sum of the individual stressors).

For example, increases in both temperature and CO₂ concentration have been shown to disproportionately lower the growth rate of some tropical corals.

Changes in ocean circulation, oxygen concentration, and acidification, along with bottom disturbances from fishing and sediment movement, are likely to affect the health and survival of organisms requiring calcium carbonate, such as shellfish and deep-sea corals.
Further research and monitoring are needed to understand the impacts of these co-occurring stressors on marine ecosystems and to identify mitigation strategies.

References

EK Towle, AC Baker, C Langdon. 2016. Preconditioning to high CO2 exacerbates the response of the Caribbean branching coral Poritesporites to high temperature stress. Marine Ecology Progress Series; 546: 75-84. DOI: 10.3354/meps11655. https://doi.org/10.3354/meps11655

E Ramirez-Llodra, PA Tyler, MC Baker, OA Bergstad, MR Clark, E Escobar, LA Levin, L Menot, AA Rowden, CR Smith, CL Van Dover. 2011. Man and the last great wilderness: human impact on the deep sea. PLoS ONE 6(8): e22588. https://doi.org/10.1371/journal.pone.0022588

RC Chambers, AC Candelmo, EA Habeck, ME Poach, D Wieczorek, KR Cooper, CE Greenfield, and BA Phelan. 2014. Effects of elevated CO2 in the early life stages of summer flounder, Paralichthys dentatus, and potential consequences of ocean acidification. Biogeosciences 11.6: 1613-1626. https://doi.org/10.5194/bg-11-1613-2014 

GG Waldbusser, EP Voigt, H Bergschneider, MA Green, RIE Newell. 2011. Biocalcification in the eastern oyster (Crassostrea virginica) in relation to long-term trends in Chesapeake Bay pH. Estuaries and Coasts 34.2: 221-231. https://doi.org/10.1007/s12237-010-9307-0

E Ramirez-Llodra, PA Tyler, MC Baker, OA Bergstad, MR Clark, E Escobar, LA Levin, L Menot, AA Rowden, CR Smith, CL Van Dover. 2011. Man and the last great wilderness: human impact on the deep sea. PLoS ONE 6(8): e22588.

Ekstrom, J. A., Suatoni, L., Cooley, S. R., Pendleton, L. H., Waldbusser, G. G., Cinner, J. E., Ritter, J., Langdon, C., Van Hooidonk, R., Gledhill, D., Wellman, K., Beck, M. W., Brander, L. M., Rittschof, D., Doherty, C., Edwards, P. E. T., & Portela, R. (2015). Vulnerability and adaptation of US shellfisheries to ocean acidification. Nature Climate Change, 5(3), 207–214. https://doi.org/10.1038/nclimate2508

Speir, C., Ryan, G., & Mayo, C. (2016). Fisheries Economics of the United States, 2014 (NOAA Technical Memorandum, p. 246). NOAA. https://spo.nmfs.noaa.gov/sites/default/files/TM163.pdf

Wang, Z. A., Wanninkhof, R., Cai, W.-J., Byrne, R. H., Hu, X., PenSabag, T.-H., & Huang, W.-J. (2013). The marine inorganic carbon system along the Gulf of Mexico and Atlantic coasts of the United States: Insights from a transregional coastal carbon study. Limnology and Oceanography, 58(1), 325–342. https://doi.org/10.4319/lo.2013.58.1.0325

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