What Is Ocean Acidification and What Causes It?

Ocean acidification is the ongoing decrease in the pH of the Earth’s oceans, caused primarily by the absorption of carbon dioxide (CO2) from the atmosphere. This process significantly alters the ocean’s chemistry, impacting marine life and ecosystems on a global scale.

The Chemistry Behind Ocean Acidification

Ocean acidification isn’t about the ocean becoming literally acidic like lemon juice or vinegar. The ocean is naturally alkaline, having a pH value slightly above 7. The issue is that the ocean is becoming less alkaline, moving closer to neutral on the pH scale. This shift, even if small, has profound consequences.

Here’s the breakdown: When atmospheric CO2 dissolves in seawater, it reacts to form carbonic acid (H2CO3). Carbonic acid then dissociates (breaks down) into bicarbonate ions (HCO3-) and hydrogen ions (H+). It’s the increase in hydrogen ions that lowers the ocean’s pH, leading to acidification.

Furthermore, the increase in H+ ions reduces the availability of carbonate ions (CO32-). These carbonate ions are crucial building blocks for many marine organisms, particularly those that build shells and skeletons from calcium carbonate (CaCO3), such as corals, shellfish, and plankton.

The Primary Cause: Atmospheric Carbon Dioxide

The overwhelming majority of ocean acidification is caused by human activities that release vast amounts of CO2 into the atmosphere. The burning of fossil fuels (coal, oil, and natural gas) for energy production, deforestation, and industrial processes are the primary contributors.

Before the Industrial Revolution, the atmospheric CO2 concentration was around 280 parts per million (ppm). Today, it’s over 415 ppm and continuing to rise. The ocean has absorbed approximately 30% of the CO2 released into the atmosphere since the start of the Industrial Revolution, acting as a significant carbon sink. While this absorption initially helped to mitigate climate change by reducing the greenhouse effect, it’s now leading to significant and detrimental changes in ocean chemistry.

Impacts on Marine Life

Ocean acidification poses a serious threat to a wide range of marine organisms and ecosystems. Organisms that build shells and skeletons from calcium carbonate are particularly vulnerable.

• Shellfish: Oysters, clams, mussels, and other shellfish struggle to build and maintain their shells in more acidic waters. This can lead to slower growth, weaker shells, and increased mortality rates, affecting aquaculture and wild populations.

• Corals: Coral reefs are among the most biodiverse ecosystems on Earth. Ocean acidification weakens coral skeletons, making them more susceptible to erosion, disease, and bleaching. This ultimately leads to the degradation and loss of coral reefs.

• Plankton: Many species of plankton, which form the base of the marine food web, also rely on calcium carbonate for their shells. Ocean acidification can disrupt plankton populations, with cascading effects throughout the entire ecosystem.

• Fish: While fish don’t build shells, they can still be affected by ocean acidification. It can impact their physiology, behavior, and reproductive success. Some fish species may struggle to regulate their internal pH in more acidic waters, affecting their oxygen uptake and overall health.

• Ecosystem Disruption: The interconnectedness of marine ecosystems means that the impacts of ocean acidification on one species can ripple through the entire food web. Changes in plankton populations can affect fish populations, which in turn can affect seabirds and marine mammals.

Addressing Ocean Acidification

The most effective way to combat ocean acidification is to reduce atmospheric CO2 emissions. This requires a global effort to transition to renewable energy sources, improve energy efficiency, and protect and restore forests.

Beyond reducing emissions, other potential strategies include:

• Ocean Alkalinity Enhancement: This involves adding alkaline substances to the ocean to neutralize acidity. However, this is a complex and controversial approach with potential environmental risks.

• Carbon Capture and Storage: This involves capturing CO2 from industrial sources and storing it underground or in the ocean.

• Protecting and Restoring Coastal Ecosystems: Seagrass beds and mangrove forests can absorb CO2 from the atmosphere and help to buffer against ocean acidification in local areas.

Frequently Asked Questions (FAQs) About Ocean Acidification

H2 What is the pH Scale and How Does it Relate to Ocean Acidification?

The pH scale measures the acidity or alkalinity of a solution. It ranges from 0 to 14, with 7 being neutral. Values below 7 are acidic, and values above 7 are alkaline (or basic). Ocean acidification is a decrease in the ocean’s pH value, meaning it is becoming less alkaline, even though it remains above 7. A change of just one pH unit represents a tenfold change in acidity. Therefore, even small changes in pH can have significant impacts on marine life.

H2 Is Ocean Acidification the Same as Climate Change?

No, ocean acidification and climate change are distinct but related problems. Both are caused by the increase in atmospheric CO2, but they have different effects. Climate change refers to the warming of the planet due to the greenhouse effect caused by CO2 and other greenhouse gases. Ocean acidification specifically refers to the change in ocean chemistry caused by the absorption of CO2. Both pose significant threats to the environment.

H2 What are the Specific Impacts of Ocean Acidification on Coral Reefs?

Ocean acidification reduces the saturation state of aragonite, a form of calcium carbonate that corals use to build their skeletons. This makes it more difficult for corals to build and maintain their skeletons, leading to slower growth, weaker structures, and increased susceptibility to erosion and disease. Combined with rising ocean temperatures (also due to climate change), ocean acidification exacerbates coral bleaching, a phenomenon where corals expel their symbiotic algae, leading to their starvation and death.

H2 How Does Ocean Acidification Affect the Marine Food Web?

Ocean acidification can disrupt the marine food web at multiple levels. It directly affects organisms at the base of the food web, such as plankton, which are crucial for supporting larger organisms. Changes in plankton populations can have cascading effects throughout the food web, affecting fish populations, seabirds, and marine mammals. The loss of key species can destabilize entire ecosystems.

H2 Which Areas of the Ocean are Most Vulnerable to Acidification?

Polar regions are particularly vulnerable to ocean acidification because cold water absorbs more CO2. Coastal areas are also more susceptible due to runoff from land, which can contain pollutants and nutrients that exacerbate acidification. Upwelling zones, where deep, CO2-rich water rises to the surface, are another area of concern.

H2 Can Ocean Acidification be Reversed?

Reversing ocean acidification entirely would require a significant and rapid reduction in atmospheric CO2 concentrations, bringing them back to pre-industrial levels. While this is a long-term goal, it’s unlikely to be achieved in the near future. Mitigation efforts, such as reducing emissions and protecting coastal ecosystems, can help to slow the rate of acidification and protect vulnerable areas.

H2 What is Being Done Globally to Address Ocean Acidification?

International collaborations, such as the Global Ocean Acidification Observing Network (GOA-ON), are working to monitor ocean acidification and understand its impacts. Many countries have implemented policies to reduce CO2 emissions and protect marine ecosystems. Research is also ongoing to explore potential mitigation strategies, such as ocean alkalinity enhancement and carbon capture.

H2 What Can Individuals Do to Help Reduce Ocean Acidification?

Individuals can take several actions to reduce their carbon footprint and help combat ocean acidification. These include:

• Reducing energy consumption by using energy-efficient appliances, conserving electricity, and driving less.
• Supporting renewable energy sources.
• Eating sustainable seafood.
• Reducing waste and recycling.
• Advocating for policies that address climate change and ocean acidification.

H2 Are There Any Benefits to Increased CO2 in the Ocean?

While some marine plants might initially experience increased growth due to higher CO2 levels, the overall effects of ocean acidification are overwhelmingly negative. The benefits are minimal and do not outweigh the detrimental impacts on calcifying organisms, ecosystems, and the marine food web.

H2 How Does Ocean Acidification Compare to Other Environmental Threats Facing the Oceans?

Ocean acidification is one of several major threats facing the oceans, alongside climate change, pollution, overfishing, and habitat destruction. These threats often interact and exacerbate each other. For example, rising ocean temperatures due to climate change can make corals more vulnerable to ocean acidification.

H2 Is There a Threshold of Ocean Acidity Beyond Which Impacts Become Irreversible?

While there isn’t a single, universally defined threshold, scientists are concerned that exceeding certain levels of acidification could lead to irreversible changes in marine ecosystems. The loss of coral reefs, the decline of shellfish populations, and the disruption of the marine food web could have long-lasting and potentially irreversible consequences.

H2 What Role Does Ocean Observing Play in Understanding and Addressing Ocean Acidification?

Ocean observing systems are crucial for monitoring ocean acidification, tracking its progress, and understanding its impacts on marine life. Data collected from these systems helps scientists to develop models, predict future changes, and inform policy decisions. The GOA-ON network plays a vital role in coordinating ocean observing efforts globally and ensuring that data is shared and used effectively. It provides necessary baseline information to track long-term changes and inform effective mitigation strategies.