Ocean Acidification

The oceans’ absorption of carbon dioxide (CO2) from the atmosphere is causing fundamental changes in seawater chemistry. CO2 reacts with water to form carbonic acid, which makes seawater more acidic. This process, known as ocean acidification (or OA) has a range of potentially harmful consequences for marine life.

Photo: Jeri Cusimano

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    What is Ocean Acidification?

    20 Facts about Ocean Acidification

    20 Facts about Ocean Acidification is a fact sheet explaining the chemistry of OA, why it’s happening and how it is affecting marine ecosystems worldwide

    Ocean acidification (or ‘OA’) is a decrease in seawater pH that is primarily caused by the ocean’s uptake of carbon dioxide (CO2) from the atmosphere. Excess CO2 generated by humans’ use of fossil fuels, and deforestation has been accumulating in the atmosphere since the industrial revolution. About one quarter of this CO2 adsorbed by the oceans, where it reacts with water molecules to form carbonic acid. As a result, the average seawater pH has already dropped by 0.1 units, a 30% increase in acidity. If atmospheric CO2 levels continue to climb at the present rate, ocean acidity will double by the end of this century. Want to keep learning? Read answers to frequently asked questions about OA; keep current on OA news; find information resources; view real-time OA monitoring data for the Pacific Northwest; and learn about NOAA’s OA Program.

    OA in Puget Sound

    OA Blue Ribbon PanelOur region is experiencing ocean acidification sooner and more severely than expected, due to a combination of human and natural causes. Wind-driven currents along our coast draw deep, naturally low-pH seawater upwards, where it mixes with the surface layer acidified by human-generated CO2. In Puget Sound,  this ‘doubly acidified’ water can become even more corrosive when runoff loaded with nutrients (mostly nitrogen and phosphorus from sewage, fertilizer, and manure) promotes the growth of algae blooms that release even more CO2 as they decay. Some of the lowest pH levels ever observed have been recorded in Hood Canal. State and federal agencies, scientists, tribes, shellfish growers and NGOs are working together to address OA in our region.

    What does OA mean for Marine Life?

    As ocean pH drops, marine organisms like oysters, pteropods and corals have to work increasingly hard to get enough carbonate ion (CO32-) from seawater to build their calcium carbonate shells and skeletons. This extra effort means that these organisms have less energy to spend on important activities like feeding, growth and reproduction. Juveniles seem to be especially vulnerable to acidification; shellfish hatcheries now monitor seawater chemistry carefully to avoid exposing their larvae to corrosive conditions that can kill them overnight. Even animals that don’t have shells are feeling the effects of acidification. OA has been shown to interfere with some fishes’ ability to avoid predators, and high levels of dissolved CO2 also seems to slow some animals’ metabolism, particularly in the context of ocean warming and hypoxia (low oxygen levels). Through direct and indirect effects, OA threatens the survival of species ranging from the tiny plankton that fuel the marine food web to the shellfish we harvest to our precious coral reefs. Want to keep learning? The Seattle Times and Sightline Institute have both published excellent series about OA and it’s impacts in the Northwest and elsewhere. Hear Taylor Shellfish spokesman Bill Dewey talk about how Washington’s shellfish industry is struggling to adapt to OA. NOAA Fisheries scientists are trying to understand how OA will affect local wild species.

    What OA is not….

    • Because our oceans are buffered against extreme pH changes by dissolved salts, seawater cannot become truly acidic (i.e. drop below pH 7). The term “acidification” refers to a pH shift towards the acidic end of the pH scale; similar to the way we describe an increase in temperature from -20°C to 0°C (-4°F to 32°F) as “warming”, even though it’s still cold.
    • Seemingly small changes in pH are not insignificant. The pH scale, like the Richter scale, is logarithmic; that means pH 7 is 10 times as acidic as pH 8. Because most animals and plants have a narrow pH ‘comfort zone’, even a small change in acidity can disrupt a number of vital functions like respiration and reproduction.
    • OA is not a future threat; it is already happening, and having serious impacts on Washington State’s marine resources, and the people who depend upon them.
    • OA is not just an “oyster problem.” Like the ‘canary in the coal mine’, the vulnerability of Pacific oysters has alerted us of much broader species impacts. Unless we do something, soon, the marine food web may change in dramatic and unpredictable ways as more and more species struggle to cope with changing seawater chemistry.

    The Early Days

    The ocean acidification story literally broke here in the Pacific Northwest in the late-2000s, when oyster larvae in Puget Sound shellfish hatcheries began dying by the billions. At first, hatchery managers suspected a pathogen, but a seminal paper published that year by scientists at NOAA’s Pacific Marine Environmental Laboratory suggested that unusually corrosive seawater might be responsible for the Pacific Northwest oyster crisis. Scientists and shellfish growers determined that unexpectedly high levels of dissolved CO2 in seawater along the West Coast was driving seawater pH down to levels capable of dissolving juvenile oysters’ shells. With funds secured by WA Senator Maria Cantwell, OA sensors were deployed near major Washington shellfish hatcheries, an act that Taylor Shellfish spokesman Bill Dewey likened to “putting headlights on a car.” These sensors allowed hatchery managers to track the approach of corrosive seawater, and temporarily close off their intake pipes to protect vulnerable larvae. Real-time OA monitoring provided Washington’s valuable shellfish industry, which generates about $270 million annually and supports over 3200 jobs, with a short-term solution to OA-induced mortalities.

    Washington Takes the Lead

    As awareness of threat of OA to Washington’s economy and environment increased, entities around the state began to take action. WSG and partners established the California Current Acidification Network (C-CAN), a consortium of scientists, resource managers and shellfish growers, and also began investing in OA research. Science and environmental organizations hosted forums and campaigns to educate the public about the issue. In 2011, WSG hosted an Ocean Acidification Symposium attended by over 200 scientists, policy makers, tribal leaders and shellfish industry representatives. At this event, former King Co. Executive Ron Sims challenged the diverse audience to work together to address the problem, prompting Governor Chris Gregoire to convene the Washington State Blue Ribbon Panel on Ocean Acidification, making Washington the first state in the nation to tackle ocean acidification at this level. WSG joined the EDF, WA Dept. of Ecology, NOAA and private foundations to fund the Panel, and dedicated it’s own staff to coordinate the process. WSG staff also edited the Panel’s Scientific Summary and authored a review of OA adaption strategies. In it’s final report, the Panel recommended monitoring acidification trends and effects, investigating its causes, building capacity for adaptation and remediation, and enlisting diverse constituencies to addressing the problem.

    A Continued Focus

    Washington’s next Governor, Jay Inslee, is maintaining state-level momentum around OA and it’s root cause: CO2 emissions. The 2013 state legislature established the Washington Marine Resources Advisory Council to carry forth the recommendations of the Blue Ribbon Panel on OA, and helped create the Washington Ocean Acidification Center at the University of Washington. Washington’s leadership has spawned similar efforts on both coasts: the California Ocean Sciences Trust convened the West Coast OA and Hypoxia Science Panel, comprising experts from California, Oregon, Washington and British Columbia. Maine and Maryland have each established their own OA Task Force to advise state government on regional OA mitigation and adaptation strategies. WSG has institutionalized its commitment to OA by becoming the first Sea Grant program in the nation to dedicate a Marine Advisory Specialist to this issue. WSG continues to initiate and support research, produce educational resources, and work with partners, state and tribal governments, and the public to address OA impacts in our region.

OA in Washington State

Our state is experiencing ocean acidification sooner and more severely than expected, due to a combination of human and natural causes. Washington Sea Grant (WSG) has been involved in regional efforts to understand and address ocean acidification since corrosive seawater was first suspected as the cause of unexplained die-offs in West Coast oyster hatcheries. WSG continues to actively engage in OA science and policy at state and local levels.

Ocean acidification in the Pacific Northwest

Ocean Acidification in the Pacific Northwest is a fact sheet summarizing our growing understanding of the causes and consequences of OA in the region’s marine waters

Community Engagement

WSG connects you to scientific information and OA experts, through education, presentations, and classroom visits.

  • In September 2016, regional experts and resource managers representing Washington Coastal Treaty Tribes, federal and state agencies, academia, and NGOs convened for a visioning workshop to discuss the designation of Washington’s north outer coast as a sentinel site for ocean acidification. The Olympic Coast Ocean Acidification Sentinel Site (OASeS) workshop was co-sponsored by NOAA’s OA Program, the Office of National Marine Sanctuaries, and Olympic Coast National Marine Sanctuary and facilitated by Washington Sea Grant. A steering committee was put into place in the fall of 2019 to continue these efforts.

  • Members of WSG were involved in the Washington Marine Resources Advisory Council (MRAC) meeting. MRAC creates policy recommendations and engages in outreach addressing OA in Washington State. The most recent meeting was in June of 2021.

  • Washington Sea Grant was involved in the fifth NOAA West Coast Acidification Cruise, which set sail in May 2016 to study OA along the entire California Current system, from Baja California to the northern tip of Vancouver Island. This cruise aboard the R/V Brownincluded studies on harmful algal blooms and pteropods. Along the way, the scientists blogged some of their experiences- including explanations of OA chemistry and deployment of instruments. The team also got a chance to share their research throughout the trip. In San Francisco, scientists disembarked for some fun at the Exploratorium, explaining Ocean Acidification to eager crowds, while in Seattle, elementary students got a tour the R/V Brown led by members of the NOAA Corps.
  • Meg Chadsey (WSG) worked with Chase Williams (UW) to coordinate and execute outreach efforts on behalf of a Sea Grant funded study investigating the effects of OA on Coho salmon. This study is led by Evan Gallagher of the UW School of Public Health.
    WSG-funded postdoc Chase Williams shows Federal Way School District middle school students a video in which he challenges juvenile Coho salmon with future levels of carbon dioxide to test their ability to avoid predator scent.
  • Washington Sea Grant’s OA team helped facilitate conceptualization of the Olympic Coast National Marine Sanctuary’s Sentinel Site program, which uses near shore monitoring to follow environmental change.
  • EarthEcho’s Ocean Acidification expedition, Shell Shocked, brought young students to the Pacific Northwest to learn about the effects of decreased oceanic pH, aided by Meg Chadsey and Washington Sea Grant.
  • Meg Chadsey, WSG’s Ocean Acidification specialist and head of the WSG OA team, has been serving as the Sea Grant liaison to NOAA’s Pacific Marine Environmental Laboratory.

We also have several on-going projects in the community:

What can you do about OA? More than you think!

While it’s true that the only long-term solution to OA is a global reduction in COemissions, there are things we can do to mitigate OA locally. Visit our OA action page to find out how you can help reduce ocean acidification.

Research Projects

WSG supports a strong OA research program. Since 2010, we’ve invested almost $1.5 million to improve our understanding of how Pacific Northwest marine species will be affected by OA, and ways to mitigate these impacts.


In the News

Due to a combination of human activities and natural factors, acidification in the Pacific Northwest is particularly severe. The region has also become a hotspot for both OA science and policy. Some recent developments: