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‘Osteoporosis of the Sea’: Rising Ocean Acidification Imperils Sea Life

Norway—the lives of many depend on the sea.  ©Ximonic (Simo Räsänen)/Wikimedia CC BY-SA 3.0
Norway—the lives of many depend on the sea. ©Ximonic (Simo Räsänen)/Wikimedia CC BY-SA 3.0

Oceans play a vital role in the health and well-being of planet Earth. They support much more than the life within them. They provide life and livelihood to many who live on or by the sea. They also absorb excess carbon dioxide from the atmosphere. As such, these carbon sinks absorb more carbon dioxide (CO2) from the atmosphere than they release. So that should be a good thing, right? 

The atmospheric concentration of CO2 has increased by almost 48% since the late 1700s. Some of it returns to the Earth, where it's stored in forests and oceans. These increased CO2 levels are wreaking havoc in the planet's largest water bodies by causing ocean acidification. 

What is Ocean Acidification?

Ocean acidification refers to the lowering of pH levels in the world’s seas. While ocean acidification can occur naturally, the current increased acidification is believed to be largely due to human activities, especially the burning of fossil fuels.

Here's how ocean acidification works: Once CO2 dissolves in water, it undergoes chemical changes. As it dissolves, it combines with water, creating carbonic acid. The carbonic acid further breaks down, creating hydrogen and bicarbonate ions. When too few carbonate ions remain, an imbalance occurs, lowering the water's pH and increasing its acidity.

Chart showing lowering of seawater pH.  ©University of Hawaii/Wikimedia CC BY-SA 4.0
Chart showing lowering of seawater pH. ©University of Hawaii/Wikimedia CC BY-SA 4.0

Carbon Dioxide in Water

Carbon dioxide is released into the atmosphere through various avenues, including exhalation by humans and animals, the burning of fossil fuels, and deforestation. There is a natural cycle of oxygen and CO2, with humans and animals breathing in oxygen and exhaling CO2, while plants take in CO2 and use it to grow, giving off oxygen in the process.

55.8 million years ago, the Earth's temperature increased by about 9°F (5°C) attributed to increased levels of CO2.

Oceans hold much of the CO2 generated; in fact, they take in roughly 30% of what was released into the atmosphere.

Scientists, studying rock and soil samples, discovered that nearly 56 million years ago, the Earth's temperature increased by about 9°F. Scientists attribute this to increased levels of CO2 and speculate that it may have been due to increased volcanic eruptions, extensive wildfires, or dissolution of ocean sediments.

Measuring Ocean Acidification 

Liquids are measured on a pH scale of 0 to 14 based on the concentration of hydrogen ions. Pure water has a pH of 7, or neutral. Anything below 7 is acidic, and anything higher is alkaline.

Today's average ocean water pH stands at 8.1. Before the Industrial Revolution, when humans began using fossil fuels for manufacturing, the level was 8.2. And while that change may not look like much, the pH scale is measured logarithmically. So, for one pH unit lowered, acidity increases by a factor of 10. Put another way, today’s oceans are about 25% more acidic than in the late 1700s.

Perils of Acidic Oceans

Ocean acidification is sometimes referred to as “osteoporosis of the sea.” Animals, like oysters and corals, use calcium and carbonate to build shells and skeletons. Four types of carbon—dissolved CO2, carbonate, carbonic acid, and bicarbonate—should exist in a balance in ocean water. But the ideal ratio is no longer maintained as CO2 increases. The carbonate ion concentration lessens, creating bicarbonate due to the higher level of CO2.

Ocean acidification impedes calcification.  ©NOAA/Wikimedia
Ocean acidification impedes calcification. ©NOAA/Wikimedia

With ocean acidification, smaller amounts of carbonate ions become available, meaning there is less calcium carbonate to construct or preserve hard shells and skeletons. Clams, corals, mussels, and oysters, for example, hold a vital role in the food chain, but when the pH drops, these animals' shells and skeletons are weakened.

 Effects of ocean acidification—ragged, dissolving shell ridges. ©NOAA Photo Library CC BY 2.0
Effects of ocean acidification—ragged, dissolving shell ridges. ©NOAA Photo Library CC BY 2.0

Fish may also be affected by ocean acidification—researchers studying sardine-like grunion off the California coast found their larvae suffered an increased mortality rate. More studies on fish are underway.

Harvard postdoctoral researcher Valentina Di Santo studied the problem in skates in laboratory conditions. She found that they seemed to grow faster while their wings' cartilage skeleton grew heavier. With a heavier skeleton, it takes more energy to swim long distances, which could affect migration.

Addressing Ocean Acidification

While the most effective way to reduce ocean acidification may be to limit the use of fossil fuels, there are other solutions.

For instance, when ocean acidification caused a drastic impact on the West Coast's shellfish industry during the 2000s, the National Oceanic and Atmospheric Administration (NOAA), along with the U.S. Integrated Ocean Observing System (IOOS), developed an early warning system for approaching acidic seawater. This system allows hatcheries to schedule fish production for times when water quality is favorable.

Hatcheries can schedule fish production when water quality is favorable. 

Another localized solution might come from aquatic plant colonies like the giant kelp forests off the California coastline because they store CO2 and release oxygen. And scientists have seen a decrease in CO2 in the surface waters around the kelp.

In the Great Barrier Reef off Australia, scientists injected alkalinity into the reef in a process called artificial ocean alkalinization (AOA) to counter the effect of about four years of increased ocean acidification.

Raising Awareness About Ocean Acidification

The most effective way to prevent further acidification of the oceans is to limit the release of CO2 into the atmosphere. This can be accomplished by reducing the use of fossil fuels. Another way to help, as NOAA advocates, is to raise awareness of the problem. They suggest participating in habitat restoration efforts or talking about ocean acidification to people whose businesses could be impacted by its harmful effects.

While the buildup of CO2 in the oceans is creating a slight decrease in the water's pH levels, it is already impacting sea life and people who depend on the oceans for their primary food and income source. And the problem is expected to increase: In environmental scientist and marine ecologist Dr. Jane Lubchenco's words, ocean acidification is “climate change's equally evil twin.” It is impacting life on this planet in significant ways, but through timely, sustained effort, the oceans can thrive.


*Cassie Journigan is a writer who lives in the north-central region of Florida in the United States. She focuses on issues related to sustainability. She is passionate about numerous topics, including the Earth’s changing climate, pollution, social justice, and cross-cultural communications.


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