Examining Ocean Acidification on World Oceans Day

photo of the earth from spaceIncreasing carbon dioxide levels in the atmosphere and oceans are resulting in chemical changes known as “ocean acidification.” These changes may pose risks for some marine species and ecosystems, as well as for the coastal communities that rely on them for food and commerce.

For World Oceans Day, we explore ocean acidification, its potential effects, and federal efforts to track and reverse its course.

How it happens

Scientists estimate that the oceans have absorbed about 30% of the carbon dioxide emitted by humans over the past 200 years. As the amount of carbon dioxide in the atmosphere increases, the oceans absorb more of it. It then reacts with the water to form carbonic acid. As a result, the average acidity of surface ocean water has increased by about a quarter since the 1700s.

Figure 1: Atmospheric Carbon Dioxide Concentration, 1700-Present(Excerpted from GAO-14-736)

Effects of acid

In addition to increasing acidity, the higher levels of carbon dioxide in the oceans cause chemical reactions that reduce what is known as the “saturation state” of certain calcium carbonate minerals. Lower “saturation states” mean some marine life will need to use more energy to build shells or skeletons.

Figure 2: Modeled Aragonite Saturation State of Surface Oceans, 2000-2099(Excerpted from GAO-14-736)

So what does ocean acidification mean for marine species, ecosystems, and coastal communities?

  • Some marine species, such as oysters, may struggle to form or keep their shells, or have to alter their behavior, potentially affecting their survival.
  • Marine ecosystems could change, altering, for example, predator and prey relationships.
  • Coastal fishing and tourism industries could see changes in their economy.

Figure 3: Pacific Oyster Larvae Raised under More Favorable Ocean Conditions (Upper) and under Acidified Conditions (Lower) (Excerpted from GAO-14-736)

However, the scientific understanding of these effects is still developing, and there’s uncertainty about their scope and severity. For example, can species adapt to changes in ocean chemistry?  One study we reviewed noted that it might be possible for some coral species to evolve a mechanism that would enable them to calcify at normal rates even in waters with lower carbonate ion concentrations, although this type of adaptation has not been documented in coral.

Federal efforts

The Federal Ocean Acidification and Monitoring Act directed the National Oceanic and Atmospheric Administration and other federal agencies to take a number of steps to address ocean acidification. For example, NOAA and other agencies have

  • established an interagency working group composed of representatives from 11 federal agencies, including the EPA and USDA;
  • developed a research and monitoring plan that includes using NASA satellites collecting data on ocean ecology and sharing that information with researchers; and
  • supported relevant science, including multiple National Science Foundation-funded studies on changes to ocean chemistry.

However, when we examined what the agencies were doing, we found they had yet to complete other steps required by the act, including clearly defining each agency’s role in implementing the research and monitoring plan.

We made 4 recommendations to improve the overall federal response to ocean acidification. To learn more about our recommendations, as well as the studies we reviewed and the work being done by federal agencies, check out the full report.


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