Oceans and Coasts

Ocean Acidification



Lessons and Activities

Real World Data

Background Information

Career Profiles

For more than 200 years, or since the industrial revolution began, the concentration of carbon dioxide (CO2) in the atmosphere has increased due to the burning of fossil fuels and land use change(e.g. increased car emissions and deforestation). During this time, the pH of surface ocean waters has fallen by 0.1 pH units. The pH scale, like the Richter scale, is logarithmic, so this change represents approximately a 30 percent increase in acidity.

pteropod shell
At the top of the diagram, a pteropod shell is shown dissolving over time in seawater with a lower pH. When CO2 is absorbed by the ocean from the atmosphere, the chemistry of the seawater is changed. (Image from NOAA PMEL)

The ocean absorbs about 30% of the CO2 that is released in the atmosphere, and as levels of atmospheric CO2 increase, so do the levels in the ocean. When CO2 is absorbed by seawater, a series of chemical reactions occur resulting in the increased concentration of hydrogen ions. This increase causes the seawater to become more acidic and causes carbonate ions to be relatively less abundant.

Carbonate ions are an important building block of structures such as sea shells and coral skeletons. Decreases in carbonate ions can make building and maintaining shells and other calcium carbonate structures difficult for calcifying organisms such as oysters, clams, sea urchins, shallow water corals, deep sea corals, and calcareous plankton. The pteropod, or "sea butterfly", is a tiny sea creature about the size of a small pea. Pteropods are eaten by organisms ranging in size from tiny krill to whales and are a major food source for North Pacific juvenile salmon. When pteropod shells were placed in sea water with pH and carbonate levels projected for the year 2100, the shells slowly dissolved after 45 days. Researchers have already discovered severe levels of pteropod shell dissolution in the Southern Ocean, which encircles Antarctica. Pteropods are small organisms, but imagine the impact if they were to disappear from the marine ecosystem!

Changes in ocean chemistry can affect the behavior of non-calcifying organisms as well. The ability of certain fish, like pollock, to detect predators is decreased in more acidic waters. Recent studies have shown that decreased pH levels also affect the ability of larval clownfish to locate suitable habitat. When subjected to lower pH levels, the larval clownfish lost their chemosensory ability to distinguish between their favored and protective anemone habitat among the reefs and unfavorable habitats like mangroves. Additionally, greater acidity impairs their ability to distinguish between the "smell" of their own species and that of predators. These two factors create an increased risk of predation. When these organisms are at risk, the entire food web may also be at risk. Ocean acidification is expected to impact many ocean species to varying degrees. While some species will be harmed by ocean acidification, photosynthetic algae and seagrasses may benefit from higher CO2 conditions in the ocean, as they require CO2 to live just like plants on land.

Estimates of future carbon dioxide levels, based on business as usual emission scenarios, indicate that by the end of this century the surface waters of the ocean could be nearly 150% more acidic, resulting in a pH that the oceans haven’t experienced for more than 20 million years.

Ocean acidification is currently affecting the entire world’s oceans, including coastal estuaries and waterways. Today, more than a billion people worldwide rely on food from the ocean as their primary source of protein. Approximately 20% of the world’s population derives at least 1/5 of its animal protein intake from fish. Many jobs and economies in the U.S. and around the world depend on the fish and shellfish that live in the ocean.

Over the last decade, there has been much focus in the ocean science community on studying the potential impacts of ocean acidification. NOAA's Ocean Acidification Program serves to build relationships between scientists, resource managers, policy makers, and the public in order to research and monitor the effects of changing ocean chemistry on economically and ecologically important ecosystems such as fisheries and coral reefs.

Since sustained efforts to monitor ocean acidification worldwide are only beginning, it is currently impossible to predict exactly how ocean acidification impacts will cascade throughout the marine food chain and affect the overall structure of marine ecosystems. With the pace of ocean acidification accelerating, scientists, resource managers, and policymakers recognize the urgent need to strengthen the science as a basis for sound decision making and action.

Education Connection

The resources included in this collection will provide support to teachers who are educating students about the cause and effects of ocean acidification. Some of the websites help teachers to provide background information in the form of videos and other multimedia activities. Links to data sources allow students to access real-time information about carbon dioxide levels in seawater and in the atmosphere. Lessons are included that will provide ideas on how to use this data with students. Ocean acidification is a problem impacts the ocean ecosystem as well as commercial industries like oyster farms. This topic can be taught in conjunction with lessons about food webs and ecosystems, the environmental impacts of climate change and CO2 emissions, and chemistry lessons concerning real-life applications.

Collection Created November 2013

Adapted from material provided by NOAA Ocean Service and NOAA’s Pacific Marine Environmental Laboratory.

A More Acidic Arctic? NOAA Deploys First Buoy in Region to Monitor Levels of CO2

September 5, 2013 (NOAA)
NOAA’s Pacific Marine Environmental Laboratory in partnership with the Marine Research Institute in Iceland deployed the first high-latitude ocean acidification monitoring buoy in the Atlantic Ocean in early August. The moored buoy is the first of its kind to be deployed north of the Arctic circle in a region where very little is known about how carbon dioxide (CO2) is entering the ocean environment.... Read More

Study Finds that Ocean Acidification is Accelerated in Nutrient Rich Areas

September 24, 2012 (NOAA)
Carbon dioxide released from decaying algal blooms, combined with ongoing increases in atmospheric carbon emissions, leads to increased levels of ocean acidification, and places additional stress on marine resources and the coastal economies that depend on them, according to a new study published today.... Read More

An Upwelling Crisis: Ocean Acidification

Thursday, October 29, 2009 (NOAA)
Richard Feely walks through the Pike Place fish market admiring the bounty and diversity of marine treasures on display at the market—rows and rows of mussels, clams, scallops, tuna, and other seafood favorites are piled high on open beds of shaved ice. Shouts of “We fillet for free!” and “Best catch of the year!” punctuate the market hubbub.... Read More