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Our Changing Ocean

What is Ocean Acidification?

Our ocean’s chemistry is changing, causing impacts to marine life and livelihoods.

Overview
Monitoring “The Big Four”
Coastal Acidification
Freshwater Acidification
What we can do

Ocean acidification occurs when the ocean absorbs carbon dioxide. This causes a fundamental and global change in the chemistry of the ocean.

The Ocean is a Great Carbon Sponge

The ocean is a great sponge for carbon dioxide. When our ocean absorbs this carbon dioxide, it changes the chemistry of the ocean. While the ocean itself is not acidic, the absorption of carbon dioxide increases the ocean’s acidity. This can impact some marine life and the people who depend on them.
AI generated - earth as a sponge
AI-Generated image by Canva

A Timeline of Evidence

Air and ocean observing provides critical information for understanding how carbon changes in the air and sea, and in turn how acidity tracks carbon in our ocean. Over the past 250 years, the ocean has become about 26% more acidic on average globally. Ocean acidification (OA) refers to a change in ocean chemistry in response to the uptake of increasing carbon dioxide (CO2).
Keeling curve showing increased atmospheric carbon dioxide and CO2 in the ocean, resulting in lower pH, or ocean acidification.

Seawater chemistry

Increases in carbon dioxide (known as CO2) in the atmosphere drive corresponding increases in dissolved CO2 within the surface waters of our ocean. This dissolved CO2 reacts with seawater to form carbonic acid (H2CO3). Carbonic acid breaks apart to form bicarbonate ions (HCO3–) and hydrogen ions (H+). Hydrogen ions (H+) act like free agents that cause the seawater to become more acidic. We measure this using pH (H represents hydrogen ions). The free agent hydrogen ions also react with carbonate ions (CO32-) to form bicarbonate (HCO3–), making carbonate ions relatively less abundant. Next, find out why this matters next.

Basic chemistry of ocean acidification and it's effects on shelled organism. Credit: NOAA Pacific Marine Environmental Laboratory
Basic chemistry of ocean acidification and it's effects on shelled organism. Credit: NOAA Pacific Marine Environmental Laboratory

Bicarbonate as a Buffer

This is how carbonate ions help to buffer seawater against large changes in pH by reacting with some of the excess hydrogen ions and forming bicarbonate. However, carbonate ions (CO32-) are an important part of calcium carbonate (CaCO3).
Image Credit: NOAA AFSC

Monitoring "the Big four"

There are four ocean chemistry parameters we measure to understand ocean chemistry related to acidification. Researchers need to measure two of these parameters to be able to calculate the others and characterize conditions.

Learn about what we measure, and why. Download the infographic for even more. 

pH

When the ocean absorbs carbon dioxide, chemical reactions create hydrogen ions that act like free agents, able to react with other compounds. Two ways we track ocean acidification are through pH and total alkalinity (TA). pH is a measure of how many free hydrogen ions are in the seawater. The more carbon dioxide in the ocean, the more these free agents are created, causing lower pH (more acidic).

pCO2

The partial pressure of CO2 (pCO2) tells us how much carbon dioxide is in seawater. This information helps us understand ocean carbonate chemistry and biological productivity in the region. pCO2 increases when the ocean absorbs more CO2 from the atmosphere with elevated emissions.

TA

Alkalinity is the ocean’s buffering system against increasing acidity. Total alkalinity is a measure of the concentration of buffering molecules like carbonate and bicarbonate in the seawater that can neutralize acid.

DIC

Dissolved inorganic carbon (DIC) tells us how much non-biological carbon is in seawater. Inorganic carbon comes in three main forms that we measure for DIC: carbon dioxide ( CO2), bicarbonate (HCO3-), and carbonate (CO32-). Understanding DIC can help us determine the balance of carbonate forms in the ocean and the likelihood of ocean acidification.

Coastal Acidification

Local coastal processes can cause acidification.

Coastal acidification occurs from local processes that affect water chemistry. They have local effects and can threaten coastal ecosystems and communities.

  • Monitoring and modeling conditions in coastal zones is critical for tracking and predicting coastal acidification.
  • Minimizing other local stresses can help ecosystems and people manage the challenges of coastal acidification better.
  • Science-based management of coastal ecosystems can help support fisheries and coastal economies and cultures.

Coastal acidification includes local changes in water chemistry that can arise from human inputs on land as well as natural processes. 

Coastal upwelling is a natural process that brings deeper,
more acidic waters to the surface ocean in the coastal zone. Upwelling occurs primarily
on the western boundaries of continents, but the timing, duration and severity of upwelling events may increase with climate change.

Human impacts include excess nutrient run-off (e.g. nitrogen and organic carbon) from land. This runoff can cause increases in algal growth, commonly known as ‘blooms’. When these algal blooms die, they consume oxygen and release carbon dioxide and increasing acidity.

Coastal acidification can also occur with changes in water column circulation occur. Changes in wind, temperature, or salinity changes can have both natural and human causes.

The impacts of ocean acidification depend on the timing, duration, and severity of acidification, how marine life and ecosystems respond, and the effects on people who depend on healthy coastal ecosystems.

Freshwater Acidification

Aqua MODIS images courtesy Jeff Schmaltz, LANCE/EOSDIS MODIS Rapid Response Team at NASA GSFC. Caption by Kathryn Hansen.
Aqua MODIS images courtesy Jeff Schmaltz, LANCE/EOSDIS MODIS Rapid Response Team at NASA GSFC. Caption by Kathryn Hansen.

Freshwater bodies like the Great Lakes also experience acidification. Researchers project that pH, the measure of how acidic or alkaline the water body is, will decline at a rate similar to that of the oceans in response to increasing atmospheric carbon dioxide.

Absorption of carbon dioxide from the atmosphere isn’t the only source of acidification. The Great Lakes are also recovering from acid deposition. The Midwestern and Northeastern United States experienced an increase in deposition of sulfuric and nitric acids from the early 20th century until air-quality regulations mitigated this trend.

Present-day mean pH and alkalinity vary according to the geology of each lake basin, with Superior having the most acidified waters and Michigan the least acidified. In addition, considerable short-term spatial and temporal variability in pH occurs, driven largely by varying rates of photosynthesis, respiration, and seasonal mixing. There has not been any long-term robust monitoring of acidification in the Great Lakes system until recently.

Ocean Acidification Solutions

Engage Your Community

What’s at stake from ocean acidification may be different depending on where you live. As a community member, you can take a larger role in educating the public about ocean acidification.

  • Share what you know - this is an action everyone can take.
  • Join your regional coastal acidification network
  • Participate in community science for directly monitoring ocean chemistry or other activities that reduce other stressors to our marine ecosystems.
  • Help restore or protect important marine ecosystems that we rely on for food, safety and the blue economy.

Use Your Tools

The NOAA Ocean Acidification Program aims to provide information to help people adapt to the consequences of ocean acidification. Check out our near real-time data and support tools that include:

  • Maps and visualization tools to explore ocean chemistry in your area
  • Forecasts, hindcasts, and nowcasts that help you assess what's happening and what is coming
  • Multimedia resources to better understand changing ocean chemistry and share with others

Build Adaptive Capacity

NOAA works to better understand how to mitigate and adapt to acidification on local, regional and national scales. Continued research that uses innovative technologies and approaches provides better information faster.

Addressing Ocean Acidification

The OAP works closely with coastal state governments, on-the-ground networks, impacted industries, and NGOs to develop their responses to ocean acidification. See how we take action by supporting legislation development and reporting for ocean acidification research. 

Legislation & Reporting

Bioeconomic modeling to inform Alaska fisheries management

Fishing Dock in Juneau Alaska
Image credit: Allen Shimada, NOAA NMFS

Bioeconomic models are a multidisciplinary tool that use oceanography, fisheries science and social science to assess socioeconomic impacts. Funded by the Ocean Acidification Program, researchers at the Alaska Fisheries Science Center use a bioeconomic model to study the impacts of ocean acidification on Eastern Bering Sea crab, northern rock sole and Alaska cod. The goal is to predict how ocean acidification will affect abundance yields and income generated by the fisheries. This work informs the potential economic impacts of ocean acidification and future decision making and research planning.

More about this work

Effects of ocean acidification and temperature on Alaskan crabs

Red King Crab
Image credit: David Csepp, NMFS AKFSC ABL

Long-term declines of red king crab in Bristol Bay, Alaska may be partially attributed to ocean acidification conditions. These impacts may be partially responsible for the fishery closures during the 2021–2022 and 2022–2023 seasons. Researchers found that ocean acidification negatively impacts Alaskan crabs generally by changing physiological processes, decreasing growth, increasing death rates and reducing shell thickness. Funded by the Ocean Acidification Program, scientists at the Alaska Fisheries Science Center continue to investigate the responses of early life history stages and study the potential of various Alaska crabs to acclimate to changing conditions. Results will inform models that will use the parameters studied to predict the effects of future ocean acidification on the populations of red king crab in Bristol Bay as well as on the fisheries that depend on them. Fishery managers will better be able to anticipate and manage stocks if changing ocean chemistry affects stock productivity and thus the maximum sustainable yield.

More about this work

Forecasts for Alaska Fisheries

Crab pots and fishing nets in Alaska's Dutch Harbor
Image credit: Michael Theberge

Understanding seasonal changes in ocean acidification in Alaskan waters and the potential impacts to the multi-billion-dollar fishery sector is a main priority. Through work funded by NOAA’s Ocean Acidification Program, the Pacific Marine Environmental Laboratory developed a model capable of depicting past ocean chemistry conditions for the Bering Sea and is now testing the ability of this model to forecast future conditions. This model is being used to develop an ocean acidification indicator provided to fisheries managers in the annual NOAA Eastern Bering Sea Ecosystem Status Report.

ADAPTING TO OCEAN ACIDIFICATION

The NOAA Ocean Acidification Program (OAP) works to prepare society to adapt to the consequences of ocean acidification and conserve marine ecosystems as acidification occurs. Learn more about the human connections and adaptation strategies from these efforts.

Adaptation approaches fostered by the OAP include:

FORECASTING

Using models and research to understand the sensitivity of organisms and ecosystems to ocean acidification to make predictions about the future, allowing communities and industries to prepare

Closeup of oysters cupped in someone's hands

MANAGEMENT

Using these models and predictions as tools to facilitate management strategies that will protect marine resources and communities from future changes

TECHNOLOGY DEVELOPMENT

Developing innovative tools to help monitor ocean acidification and mitigate changing ocean chemistry locally

REDUCING OUR CARBON FOOTPRINT

50 more ways to reduce your carbon footprint >

On the Road

Drive fuel-efficient vehicles or choose public transportation. Choose your bike or walk! Don't sit idle for more than 30 seconds. Keep your tires properly inflated.

With your Food Choices

Eat local- this helps cut down on production and transport! Reduce your meat and dairy. Compost to avoid food waste ending up in the landfill

With your Food Choices

Make energy-efficient choices for your appliances and lighting. Heat and cool efficiently! Change your air filters and program your thermostat, seal and insulate your home, and support clean energy sources

By Reducing Coastal Acidification

Reduce your use of fertilizers, Improve sewage treatment and run off, and Protect and restore coastal habitats

TAKE ACTION WITH YOUR COMMUNITY

You've taken the first step to learn more about ocean acidification - why not spread this knowledge to your community?

Every community has their unique culture, economy and ecology and what’s at stake from ocean acidification may be different depending on where you live.  As a community member, you can take a larger role in educating the public about ocean acidification. Creating awareness is the first step to taking action.  As communities gain traction, neighboring regions that share marine resources can build larger coalitions to address ocean acidification.  Here are some ideas to get started:

  1. Work with informal educators, such as aquarium outreach programs and local non-profits, to teach the public about ocean acidification. Visit our Education & Outreach page to find the newest tools!
  2. Participate in habitat restoration efforts to restore habitats that help mitigate the effects of coastal acidification
  3. Facilitate conversations with local businesses that might be affected by ocean acidification, building a plan for the future.
  4. Partner with local community efforts to mitigate the driver behind ocean acidification  – excess CO2 – such as community supported agriculture, bike & car shares and other public transportation options.
  5. Contact your regional Coastal Acidification Network (CAN) to learn how OA is affecting your region and more ideas about how you can get involved in your community
       More for Taking Community Action