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Ocean Acidification

What is Ocean Acidification?

Ocean acidification refers to the ongoing change in the chemistry of the ocean caused primarily by the ocean's absorption of carbon dioxide from the atmosphere. For the last 250 years, the burning of fossil fuels — coal, oil, natural gas — for energy, cement production, and deforestation has been pumping carbon dioxide or CO2, into the atmosphere. The ocean absorbs about 1/4 of this excess CO2 released into the atmosphere every year. This addition of CO2 into the ocean is changing the chemistry of seawater by increasing the acidity and lowering the seawater's naturally occurring carbonate ion. CO2, when combined with water, forms a weak acid, which increases the hydrogen ion concentration in the ocean, lowering the pH and making the oceans less alkaline or more acidic. As the ocean becomes less alkaline there is a reduction in the amount of carbonate ions and calcium carbonate minerals, biologically important building blocks for many marine organisms.


This graph shows the correlation between rising levels of carbon dioxide (CO2) in the atmosphere at Mauna Loa, Hawaii, with rising CO2 levels in the nearby ocean at Station Aloha. As more CO2 accumulates in the ocean, the pH of the ocean decreases. Modified after R.A. Feely, Bulletin of the American Meteorological Society, July 2008

Since 1750, the average acidity of the ocean has increased about 30 percent. The current rate of acidification is nearly 10 times faster than any time in the past 50 million years, outpacing the ocean’s capacity to restore oceanic pH and carbonate chemistry. The rapid pace of change gives marine organisms, marine ecosystems, and humans less time to adapt, evolve, or otherwise adjust to the changing circumstances.

Many life processes, including photosynthesis, growth, respiration, recruitment, reproduction, and behavior are sensitive to carbon dioxide and pH. As a result, ocean acidification has the potential to affect a wide range of organisms, from marine invertebrates like shellfish, to photosynthesizers including phytoplankton and seagrasses, as well as vertebrates including fish in many different ways.


The absorption of excessive amounts of CO2 from the atmosphere is changing the chemistry of seawater by increasing the acidity and lowering the seawater's naturally occurring carbonate ion, a building block of the calcium carbonate required of many marine organisms to grow their shells and skeletons. Ocean acidification reduces calcification rates in shell-forming organisms such as corals and shellfish. In coastal areas with coral reefs, reef structures impacted by ocean acidification are weaker and less able to protect coastal communities from storm damage. Economically important shellfish species such as oysters, scallops, mussels, and clams are negatively impacted by reduced calcification rates brought on by ocean acidification, particularly in larval stages shell building. Other calcifying organisms like tiny sea snails known as pteropods are affected by the chemistry changes. Shelled pteropods are a critical food source for salmon, mackerel, herring, cod, and even whales.

Ocean Acidification in the Pacific Northwest

The marine waters of the Pacific Northwest are particularly vulnerable to ocean acidification. Regional marine processes including coastal upwelling exacerbate the acidifying effects of global carbon dioxide emissions. Coastal upwelling brings deep ocean water, which is rich in carbon dioxide and low in pH, up into the coastal zone. This upwelled water has spent decades circulating deep in the ocean, out of contact with the atmosphere for 30 to 50 years. This means that the waters currently upwelled onto the coast of the Pacific Northwest reflect the atmospheric carbon dioxide concentrations of the 1970s and 1980s. We will continue to see more acidifying conditions coming from upwelled waters into the future.


Other local factors that include runoff of nutrients from land, and local emissions of carbon dioxide, nitrogen oxides, and sulfur oxides, which are absorbed by seawater from the atmosphere, also impact the chemistry of the waters of the Pacific Northwest. The relative importance of these local factors varies by location. For example, acidification along the outer coast of Washington and Puget Sound is strongly influenced by coastal upwelling while acidification in shallow estuaries, including those in Puget Sound, may be influenced more by run off from fresh water sources (which are naturally low in pH) that are carrying nutrients from human and natural sources.

Puget Sound Partnership

Oyster growing in Samish Bay, Puget Sound

Shellfish along the West Coast is an $111 million industry, supplying 1000s of jobs in Oregon and Washington. Less than a decade ago, shellfish hatcheries in Oregon and Washington, essential to shellfish growers all along the West Coast, were on the verge of collapse. In 2012, scientists in Oregon found evidence that higher levels of carbon dioxide in the Pacific Ocean were responsible for the failure of oyster larvae to survive in 2005 at Whiskey Creek Shellfish Hatchery on Netarts Bay (Barton et al, 2012). Federal and state investments in monitoring of coastal seawater have helped to provide shellfish hatchery managers with real-time data on the seawater coming into their hatcheries. The data provide an early warning system, signaling the approach of cold, acidified seawater one to two days before it arrives in the sensitive coastal waters where shellfish larvae are cultivated. The data help hatchery managers schedule production when water quality is good, anticipate the need to buffer or adjust the chemistry of the water coming into their hatcheries, and avoid wasting valuable energy and other resources it water quality is poor.

What is NANOOS doing?

NANOOS is contributing observations and expertise to increase understanding of ocean acidification in the Pacific Northwest. NANOOS is partnering with shellfish growers, tribal, state and local agencies, and regional shellfish managers to collect and make available vital data for understanding and coping with ocean acidification in the Northwest.

John Payne

Since 2010, NANOOS has maintained this buoy, Cha'ba, off the coast of La Push, WA, to provide vital information on ocean conditions off the coast and near the Strait of Juan de Fuca.

In 2010, NANOOS partnered with NOAA-PMEL and relocated a buoy close to a major shellfish hatchery in Hood Canal, Washington, after a state-declared 'oyster emergency'. Also in 2010, NANOOS and the University of Washington first deployed the buoy, Cha'ba, off the coast of La Push WA, an area critical to understanding ocean water off the WA Coast and coming into Puget Sound. NANOOS is working with its partners to host pH/pCO2 sensors on several buoys in the Puget Sound and off the Oregon and Washington coast. NANOOS also serves similar data from other sources, including the shellfish industry.

Amy Sprenger

Shellfish growers provide feedback on the NVS Shellfish Growers App during a focus group with NANOOS staff.

In 2007, NANOOS worked with the National Estuarine Research Reserve System to develop a website allowing easy access to real-time water quality data from sites in Oregon, Washington and Alaska. In 2012 this website was updated with input from shellfish growers to the NANOOS Visualization System (NVS) Shellfish Growers App, providing shellfish growers and restoration managers with better and more information for decision making.

Additional Resources

20 Facts About Ocean Acidification

Ocean Acidification in the Pacific Northwest: The Facts

This fact sheet summarizes our growing understanding of the causes and consequences of ocean acidification in the Pacific Northwest marine waters.

NOAA Pacific Marine Environmental Lab Carbon Program

NOAA Ocean Acidification Program

NOAA Northwest Fisheries Science Center

Washington State Blue Ribbon Panel on Ocean Acidification

Scientific Summary of Ocean Acidification in Washington State Marine Waters

West Coast Ocean Acidification and Hypoxia Science Panel

California Current Acidification Network (C-CAN)

Ocean Acidification Around the World

An interactive tool designed to make ocean acidification understandable by tracking emerging science and providing updates on what is occurring and where.

Washington Ocean Acidification Center

Ocean Acidification.Net

An informational website to bring information on ocean acidification to scientists, policymakers, and the public. Maintained by the International Geosphere-Biosphere Programme (IGBP).

NANOOS and the Shellfish Industry

A Senior Biologist at the Pacific Shellfish Institute describes how near-real time water quality data is used to inform shellfish growers and minimize larval mortalities.

IOOS Pacific Region Ocean Acidification

Ocean Technology Transition Project

NANOOS and its partners have been awarded a grant to improve OA observing capability along the U.S. west coast.

Related NANOOS Products

NANOOS Visualization System (NVS)

NVS Shellfish Growers App

NVS Data Explorer App

NVS PRISM Cruise App

Related Videos

NOAA IOOS Video on Ocean Acidification

Washington Ocean Acidification Center

University of Washington Applied Physics Laboratory Video on the Washington Ocean Acidification Center and NANOOS

Acidity on the Halfshell

A five minute presentation by Libby Jewett of NOAA OAP.

Ocean Acidification in Puget Sound

Produced by students from the Suquamish Tribal Early College High School.

The Other CO2 Problem

Animation video by Ridgeway School students, Plymouth, UK.

Tracking an Ocean of Carbon

Narrated by Dr. Chris Sabine.

Acid Ocean

A short BBC Newsnight film on the impact of CO2 on the Ocean.

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