What is OA?

Photo at right: Illustration of the principles involved in ocean acidification, David Fierstein © 2007 MBARI

Over the past 150 years human emissions of carbon dioxide (CO2) from processes and technologies developed during the Industrial Revolution has increased CO2 concentrations in the atmosphere to 400 parts per million (ppm).

This concentration of CO2 in the atmosphere is now greater than at any other time on Earth for at least the last 800,000 years and likely 20 million years. The 105 ppm increase that has occurred during this time is greater than the increase that occurred between the last ice age and the start of the Industrial Revolution, a period of approximately 20,000 years.

As energy usage continues to increase as global economies expand and developing nations reach their energy consumption potential atmospheric CO2 levels will rise accordingly.

In response to increased CO2 levels, the oceans have absorbed approximately 525 billion tons of CO2 from the atmosphere, or about one third of the anthropogenic carbon emissions released both from industrial processes (mostly fossil fuel burning) and changes in land use practices (deforestation and urbanization). This absorption of CO2 has mitigated warming in the atmosphere, but is having negative impacts on the chemistry and biology of the oceans. When CO2 is added to the oceans it lowers the pH causing the upper ocean to become more acidic. 

The pH of ocean surface waters has already decreased by about 0.1 units from an average of about 8.21 to 8.10 since the beginning of the industrial revolution. Estimates of future atmospheric and oceanic CO2 concentrations, based on the Intergovernmental Panel on Climate Change (IPCC) CO2 emission scenarios suggest that by the year 2050 atmospheric CO2 levels could reach more than 500 ppm, and near the end of the century they could be over 800 ppm. This would result in an additional surface water pH decrease of approximately 0.3 pH units by 2100.

As the pH in the ocean decreases it reduces the availability of carbonate ions, which play an important role in shell formation for a number of marine organisms such as corals, marine plankton, and shellfish. This phenomenon, which is commonly called "ocean acidification," (OA) is a tangible manifestation of an anthropogenic phenomenon that could have profound impacts on some of the most fundamental geochemical and biological marine processes in the coming decades. Some of the smaller calcifying organisms are important food sources for higher marine organisms such as salmon and the abundance of commercially important shellfish like crabs and oysters may also decline. This rapidly emerging scientific issue and possible ecological impacts have raised serious concerns across the scientific and fisheries resource management communities and demand expanded study. 

Photo at left: The pteropod, which may make up more than 50% of the juvenile pink salmon diet, is particularly sensitive to changing acidity levels in the ocean. Photo by Russ Hopcroft, UAF.

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