Ocean acidification

The ocean is changing.

People burn fuels for energy. This puts more air into the sky. The ocean takes in this air.

This makes the water more acidic. It is harder for sea life to build shells.

Creatures like coral and snails need these shells. This can change the food for many animals. It also affects people who fish. We can help by using less fuel.

The ocean is changing in a big way. This is called ocean acidification. It happens when the sea takes in carbon dioxide from the air.

Humans release this gas when we burn fossil fuels for energy. The ocean acts like a sink. It absorbs about a quarter of these emissions.

When carbon dioxide enters the water, a chemical change occurs. It makes carbonic acid. This acid lets out hydrogen ions. These ions lower the pH of the water. A lower pH means the water is more acidic.

This change makes life hard for many sea creatures. Many animals use calcification to grow. Calcification is the way they build shells and skeletons. They need carbonate ions to do this. But the extra hydrogen ions use up those ions.

Without them, it is hard to build strong shells. Animals like corals and mollusks are at risk. This can hurt the whole food chain. It can also affect one billion people who rely on the ocean for food and jobs.

The ocean is undergoing a major chemical change. This process is known as ocean acidification. It happens as the sea absorbs carbon dioxide from the air.

This change is very important for all life on Earth. It affects how the water works and how creatures live. The ocean helps by acting as a carbon sink. It takes in about 26% of human-made carbon dioxide emissions. This helps manage the gas in our atmosphere.

There is a specific way this works in the water. When carbon dioxide enters the sea, it reacts with water. This reaction creates carbonic acid.

This acid then breaks apart into bicarbonate and hydrogen ions. The increase in free hydrogen ions lowers the pH level. A lower pH means the water is becoming more acidic. Even a small drop of 0.1 in pH is a big deal. This change represents a 26% increase in hydrogen ions.

Scientists have tracked these changes for a long time. In the pre-industrial era, CO2 levels were around 280 parts per million. Today, those levels are over 410 parts per million.

Between 1950 and 2020, the surface pH fell from 8.15 to 8.05. These rapid growth rates are unprecedented for 55 million years. This tells us the chemistry is changing very fast. We can see how much the ocean has absorbed since 1850. It holds a huge amount of the carbon we release.

This change makes life very hard for many sea animals. Many creatures use a process called calcification to grow. Calcification is how they build shells and skeletons.

They need carbonate ions to make these hard parts. However, the extra hydrogen ions use up those carbonate ions. This leaves fewer building blocks for animals like corals and mollusks.

Without enough carbonate, their shells can even begin to dissolve. This puts many species at a great risk.

These changes can hurt the whole ocean ecosystem. Many animals at the base of the food chain are at risk. This can cause a ripple effect through the entire web.

It can also affect the lives of many people. About one billion people depend on coral reefs for food and jobs. They rely on fishing, tourism, and coastal management. Reducing carbon dioxide emissions is a main way to help. This is a key goal for protecting our planet's future.

Ocean acidification refers to the ongoing decrease in the pH of the Earth's oceans. This process is driven by the absorption of carbon dioxide (CO2) from the atmosphere. As the ocean takes in this gas, its chemical balance shifts. This change is significant because it alters the fundamental chemistry of seawater. The ocean acts as a massive carbon sink for human activities. It has absorbed about 26% of all anthropogenic CO2 emissions since 1850.

This absorption helps manage atmospheric levels, but it changes the water in the process.

The mechanism of acidification begins when CO2 dissolves in seawater. Once dissolved, the CO2 reacts with water to form carbonic acid (H2CO3). This carbonic acid then dissociates, or breaks apart, into bicarbonate ions (HCO3-) and hydrogen ions (H+). The increase in the concentration of these free hydrogen ions is what lowers the pH. A lower pH value indicates that the water is becoming more acidic.

Although the ocean is still alkaline, with a pH above 8, the rising hydrogen ion concentration is a major shift. Because the pH scale is logarithmic, a small change of 0.1 represents a 26% increase in hydrogen ions.

This chemical shift directly impacts the availability of carbonate ions (CO32-). To maintain chemical equilibrium, the extra hydrogen ions combine with existing carbonate ions to create more bicarbonate. This reaction reduces the concentration of carbonate ions available in the water. This is a critical problem for marine calcifiers. These are organisms that use calcification to build their bodies. Calcification is the process of turning dissolved ions into solid calcium carbonate (CaCO3) structures.

Without enough carbonate ions, these organisms struggle to build and maintain their shells and skeletons.

Many different types of marine life are vulnerable to these changes. Mollusks, such as clams and snails, rely on stable carbonate levels. Corals are also highly sensitive because they build massive reef structures from calcium carbonate. Microscopic organisms like coccolithophores and foraminifera are also part of this group.

Even small creatures like pteropods can be affected. In some cases, the seawater can become so low in carbonate saturation that existing shells actually begin to dissolve.

This puts the very foundation of many marine habitats at risk.

Scientists have documented a rapid change in ocean chemistry over recent history. In the pre-industrial era, atmospheric CO2 levels were approximately 280 parts per million (ppm). By 2023, these levels had risen to over 410 ppm. This increase is primarily due to fossil fuel combustion and deforestation. Between 1950 and 2020, the average surface pH fell from about 8.15 to 8.05.

These rapid growth rates in CO2 are unprecedented in the last 55 million years. The ocean sink has increased in pace alongside the rise in human emissions.

The consequences of acidification extend to entire ecosystems and human societies. Reduced calcification and lowered immune responses have been observed in marine life. These changes can disrupt the food web, as many species depend on calcifying organisms for food. This could eventually lead to a decline in fish stocks. This is a major concern for the one billion people who depend on coral reefs. They rely on these reefs for fishing, tourism, and coastal protection.

A collapse in reef ecosystems would threaten these livelihoods and food chains.

Addressing ocean acidification requires looking at the broader climate system. One primary solution is the reduction of carbon dioxide emissions through climate change mitigation. Removing CO2 from the atmosphere would help reverse the acidification process. Scientists are also investigating ocean-based methods like ocean alkalinity enhancement. This would involve adding substances to the water to increase its capacity to resist pH changes. However, these methods currently have a low technology readiness level and carry many risks. Understanding the connection between the atmosphere and the ocean is vital for protecting marine life.