Ocean Acidification

The ocean is a vital part of a healthy global carbon cycle, acting as a sink for atmospheric carbon and helping to regulate the temperature of the planet. Atmospheric carbon dioxide is absorbed by the ocean, forming carbonic acid. This increase of acid, and thus hydrogen ions, effectively decreases the pH of the ocean. With rising levels of anthropogenic carbon in our atmosphere, more carbon is absorbed by the ocean and the ocean becomes more acidic. Carbonates exist in the oceans as a buffer for this reaction, and so, as the carbon dioxide is absorbed and the pH decreases, carbonates are consumed.

The second international symposium on the Ocean in a High-CO2 World, organized by UNESCO's Intergovernmental Oceanographic Commission, the Scientific Committie on Ocean Research (SCOR), the International Atomic Energy Agency (IAEA), and the International Biosphere Programme (IGBP) was held in October of 2008. The confrence results are reposted on the website of the Ocean Acidification Network.  A summary is also available, titled Science Summary of the Symposium for Policy Makers, by Carol Turley, Plymouth Maine Labratory. 

Carbonates are important to marine life that relies on calcium carbonate (CaCO3) shells. Calcium carbonate dissolves in acid and thus, these species will experience increased difficulty forming shells and other hard parts due to both the decreased availability of carbonates and the acidic environment. This will threaten organisms from calcareous plankton, to coral reef building organisms, to familiar mollusks like mussels and urchins. Acidification may also cause problems by affecting the pH of bodily fluids, which may impact metabolisms, immune systems and respiration of certain fish and invertebrates.



Studies show that the acidification of the ocean has been happening faster in recent decades than it has in the past 300 million years. This rate of change may be too fast for many species and the ocean itself to adapt to the changing conditions brought on by acidification. Some worry of mass extinctions being triggered as they have been in the geologic past.

These changes are very important, not only to the health of functioning marine ecosystems, but also to human populations that rely upon them. Millions of people in coastal communities and around the world rely on food supplies based on fish and shellfish stocks. A shortage of these stocks on a grand scale could have serious implications on global food security. Similarly, coastal communities and economies could be seriously impacted via fisheries, tourism and other industries reliant on these ecosystems and their foodwebs.

Several documentaries have been produced on the subject including “Ocean Acidification: Connecting Science, Industry, Policy and Public” from the Plymouth Marine Laboratory. Another, produced by the National Resources Defence Council entitled “ACID TEST: The Global Challenge of Ocean Acidification" features narrator Sigourney Weaver.


A good summary of the issues at hand are provided in the Scientific Synthesis of the Impacts of Ocean Acidification on Marine Biodiversity published as part of the Convention of Biological Diversity Technical Series.


A fact sheet on The Ocean in a High CO2 World is available from the Ocean Acidification Network.


Being a relatively new issue, with most research being conducted in the last decade or two, questions still remain. This user friendly FAQ provided by the Woods Hole Oceanographic Institute has the answers to many questions being asked about ocean acidification and its impacts.


For more information about this topic and more check out the Emerging Issues Publications page.

The National Oceanic and Atmospheric Administration (NOAA) has released 3 hypotheses from which their ocean acidification research plan is based. “These hypotheses are intended to provide strategic science-based guidance to the NOAA research community and to help integrate the broad range of proposed activities toward a common purpose.

Hypothesis 1. Rates and magnitude of acidification vary across time, space, and depth as a consequence of local and regional geochemical, hydrological, and biological mechanisms.

Hypothesis 2. Ocean acidification will change ecosystem structure, function, and biodiversity via both direct impacts (e.g., altered growth or survival rates) and indirect effects (e.g., food web and/or habitat changes).

Hypothesis 3. Heterogeneity in species-specific responses, local environmental and regional considerations will confer a broad range of vulnerabilities that differ both locally and regionally.

"Ocean Acidification: A National Strategy to Meet the Challenges of a Changing Ocean”

A 2010 report from the US National Research Council entitled Ocean Acidification: A National Strategy to Meet the Challenges of a Changing Ocean gives an overview of ocean acidification issues, and recommends goals moving forward. Among the recommendations, the report suggests a global network of chemical and biological observations better suited to assess ocean acidification. The report agrees that more research is needed to fully understand all the possible impacts of ocean acidification. It is expected that these impacts will not be the same for all organisms and ecosystems and some may be more vulnerable than others.

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