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.

Changes in Chemistry Impact Marine Plants and Animals

Ocean acidification also influences CO₂-driven changes in the solubility of calcium carbonate minerals (CaCO₃) used by many marine plants and animals to build their shells and skeletons.

The solubility of CaCO₃ minerals depend on the amount of dissolved carbonate ions in seawater.

More 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.

Coastal & Estuarine Acidification Stressors Need for Information What’s Next

Coastal & Estuarine Acidification

A Compounding Crisis

While increased atmospheric CO₂ is the primary driver of ocean acidification in surface ocean waters, the coastal oceans and estuaries experience additional processes – both natural and anthropogenic (human-caused) – that play a role in changing water chemistry. Natural input of nutrients to the ocean via rivers, groundwater, and atmospheric deposition promotes algae growth in estuarine waters, making these estuaries areas of high productivity. In a process known as eutrophication, additional input of nutrients to the estuary and coastal ocean (due to use of fertilizer, wastewater treatment, and changing land use) fuels additional growth of algae during the productive spring and summer seasons.

Infographic: What’s Driving The Changes to the Mid-Atlantic’s Coastal Chemistry?

If larger animals like fish and shellfish do not consume the algae blooms, the organic material will be broken down by bacteria leading to conditions of low oxygen called hypoxia.

Bacterial respiration not only consumes oxygen, but also produces CO₂, which results in seasonal decreases in pH in excess of the acidification driven by the atmospheric CO₂. This is a particularly serious issue compounding acidification in the Mid-Atlantic estuaries.

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

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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