Ocean acidification occurs when the ocean absorbs carbon dioxide from the atmosphere. This causes a fundamental and global change in the chemistry of the ocean.
Monitoring "the Big four"
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
Nutrient runoff and pollution threaten ecological productivity.

Coastal acidification impacts are changes in water chemistry caused mostly from human activities on land. They have local effects and can threaten the health of coastal residents and ecosystems.
- Fertilizer pollution drains into waterways and coastal areas.
- Small algae “bloom” due to the nutrients, starving other organisms of oxygen. Some of these blooms may be harmful to marine life and people.
- The algae die-off, releasing CO2 that acidifies the water and puts negative stress on an already compromised environment.
Coastal acidification includes local changes in water chemistry from freshwater river inputs and excess nutrient run-off (e.g. nitrogen and organic carbon) from land. Excess nutrients from runoff and fertilizers can cause increases in algal growth. When these algal blooms die, they consume oxygen and release carbon dioxide.
The ability of an ecosystem to cope with acidification is influenced by the amount of local stressors it needs to contend with, such as high nutrient input or changes in temperature or salinity. By minimizing local stresses, some ecosystems may prove more resilient to ocean acidification.
Freshwater Acidification

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.
Be the Change

Take Action within 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.

Reduce Your Footprint
There are many actions you can take to reduce your personal carbon footprint. From helping to reduce oil consumption with petrol products to making your home more energy efficient.

Adapt to Our Changing Ocean
The NOAA Ocean Acidification Program (OAP) works to build knowledge about how to adapt to the consequences of ocean acidification and conserve marine ecosystems as acidification occurs.
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.