Ocean Acidification

One of the consequences of increasing CO2 emissions with a monumental impact on the marine environment is ocean acidification. Between 1750 and 2011, the ocean has absorbed 30% of the CO2 that has been emitted by humans, resulting in ocean acidification (1). Ocean acidification occurs as the ocean absorbs CO2 which reacts with seawater to form carbonic acid (H2CO3).

When carbonic acid is formed, it results in the production of free hydrogen ions that alter the pH of the ocean and make it more acidic (lower pH). These excess hydrogen ions bond easily with existing carbonate (CO²⁻₃) in the ocean which reduces the availability of carbonate to be used by marine organisms (2).

Birchenough et al. 2017
Bednaršek et al., 2012

Many sea creatures like corals, crustaceans, snails, clams, and molluscs, rely on carbonate to bind with calcium to form calcium carbonate  (CaCO3), the essential mineral required for shell and skeleton production. As the oceans absorb more CO2 and acidify, calcifying marine organisms lose their ability to produce calcium carbonate and therefore the creatures have less growth, abundance, larval development, and therefore survival (3). 

Ocean acidification affects calcifying organisms to such an extent that there is evidence of the dissolution of their hard structures. Not only is this of concern for the ecological role of these organisms, but this signifies that many important sources of seafood are in danger as well. Coral reefs are also at risk, which in turn affects all the other organisms that rely on the coral reef ecosystem. The impacts of ocean acidification are far-reaching. Marine food webs, biodiversity, aquaculture, and therefore society, in general, are in danger as the ocean continues to absorb excess anthropogenic carbon (3).

primary polyp of juvenile Acropora millepora coral skeleton at 390 and 750 µatm pCO2 Figure modified from Wu et al. (2017)

  1.  IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151.
  2. Farmer, T. G., and Cook, J. Climate Change Science: A Modern Synthesis. Volume 1 – The Physical Climate. (2013). Springer. DOI: https://doi.org/10.1007/978-94-007-5757-8.
  3. IGBP, IOC, SCOR (2013). Ocean Acidification Summary for Policymakers – Third Symposium on the Ocean in a High CO2 World. International Geosphere-Biosphere Programme, Stockholm, Sweden.