Ocean acidification
What is ocean acidification?
How much has the ocean’s pH changed since the industrial revolution?
Why is a small change in pH a big deal?
What happens when carbon dioxide mixes with seawater?
Which animals are most harmed by ocean acidification?
What happened to pteropod shells in tests with more acidic water?
How does acidification affect clownfish?
Which sea organisms might actually benefit from higher carbon dioxide levels?
What pH level might ocean surface water reach by 2100?
Why do scientists and leaders care about ocean acidification?
An Ocean Changing from the Inside Out
Over the last 200 years, humans have changed the air around Earth by burning fossil fuels like coal, oil, and gas.
This has released more carbon dioxide into the atmosphere. About thirty percent of this extra carbon dioxide is absorbed by the ocean. That means the ocean has become more acidic—its waters are less alkaline than before.
What Does pH Mean?
Scientists measure how acidic or alkaline water is using something called the pH scale. The scale goes from 0 to 14.
A pH of 7 is neutral. Numbers lower than 7 mean the water is acidic. Numbers above 7 mean it is alkaline. Water that is acidic has more hydrogen ions, making its pH lower. Sometimes even a small change in pH can mean a big increase in acidity.
For example, the ocean’s surface water pH has fallen by 0.1 units. That may sound small, but it actually means the ocean is about 30 percent more acidic than before the industrial era .
How Carbon Dioxide Changes Ocean Water
When carbon dioxide from the air mixes with seawater, it forms a weak acid called carbonic acid. This acid then breaks apart into pieces, including hydrogen ions.
When seawater has more hydrogen ions, it becomes more acidic. This process is called
ocean acidification .
Who Is Affected in the Ocean
Some ocean animals depend on the water being a certain pH to build their shells or skeletons. Animals like oysters, clams, corals, sea urchins, starfish, and tiny pteropods need parts called carbonate ions to build calcium carbonate shells or skeletons.
When the water becomes more acidic, there are fewer carbonate ions available. That makes it harder for these animals to grow strong shells. In some cases, their shells can begin to dissolve .
In real tests, scientists put tiny ocean snails called pteropods in water with the acidity expected by the year 2100. After just 45 days, their shells started to dissolve. This is already happening today in cold waters off Antarctica.
Effects on Other Animals
Ocean acidification affects more than just shell-building animals. Fish like clownfish rely on their sense of smell to avoid predators and to find places to live.
In more acidic water, their sense of smell and ability to make good choices about where to live can be harmed . If fish cannot survive or reproduce well, the animals that eat them may also be affected.
Are Any Organisms Helped?
Not all sea life is harmed. Plants in the ocean, like algae and seagrasses, may benefit from higher levels of carbon dioxide. They can use this extra gas to grow, just like land plants . Some scientists are even studying whether growing seaweed could help reduce acidification in local areas.
What the Future May Bring
If humans continue producing carbon dioxide at current rates, the ocean’s surface pH may fall to about 7.8 by the year 2100. That would make it as acidic as it was 14 to 17 million years ago, during a warm period when many animals went extinct.
This change in pH is not just far out at sea. It is happening near coastlines and in areas called estuaries where rivers meet the ocean. Billions of people rely on ocean fish and shellfish for food and jobs. In many places, jobs depend on healthy fish populations and coral reefs.
What Scientists Are Doing
Ocean acidification is part of the larger problem of climate change. Scientists, resource managers, and leaders are working together to monitor acidification, study how it affects ecosystems, and use that information to help communities and governments make decisions.
For example, in the U.S. Pacific Northwest, young Dungeness crab are already being harmed by acidic water, prompting further study and action .
While it is still difficult to predict exactly how everything will change in the future, researchers know this problem is real and growing. A strong scientific understanding will help people act in time to protect ocean life and the communities that depend on it.
pH – A measure of how acidic or alkaline water is.
Acidic – When a substance has a low pH and high hydrogen ion level.
Alkaline – When a substance has a high pH and low acidity.
Carbon dioxide (CO₂) – A gas released when burning fossil fuels.
Carbonic acid – A weak acid formed when carbon dioxide mixes with water.
Hydrogen ion – A particle that makes water more acidic.
Carbonate ion – A particle needed by animals to build shells and skeletons.
Calcium carbonate – The material that makes up many shells and skeletons.
Pteropod – A tiny sea snail whose shell can dissolve in acidic water.
Coral – A sea animal that builds reefs using calcium carbonate.
Estuary – A coastal area where rivers meet the sea.
Algae – Simple aquatic plants that may grow faster in higher CO₂.
Seagrass – A marine plant that uses carbon dioxide to grow.
Ecosystem – A community of living things and their environment.
Larvae – Young animals that are not yet adults, like baby crab or fish.
Hypothesize – To make an educated guess and then test it (scientists use this word).
Monitor – To watch or check something over time.
Mitigate – To make something less serious or harmful.
Fossil fuels – Natural fuels like coal, oil, and gas.
Climate change – Long-term changes in Earth’s weather and temperature.
► COMPREHENSION QUESTIONS
— please answer with complete sentences
What is ocean acidification?
How much has the ocean’s pH changed since the industrial revolution?
Why is a small change in pH a big deal?
What happens when carbon dioxide mixes with seawater?
Which animals are most harmed by ocean acidification?
What happened to pteropod shells in tests with more acidic water?
How does acidification affect clownfish?
Which sea organisms might actually benefit from higher carbon dioxide levels?
What pH level might ocean surface water reach by 2100?
Why do scientists and leaders care about ocean acidification?
► From EITHER/OR ► BOTH/AND
► FROM Right/Wrong ► Creative Combination
THESIS — Argue the case that small changes in things are no big deal, so why be worried?
ANT-THESIS — Argue the case that small changes only look small and may be a very big deal indeed.
SYN-THESIS — Create a perspective about “small changes” that includes both perspectives.
