Ocean Acidification: Air Pollutants' Impact On Marine Environments

Ocean acidification is a significant and harmful consequence of excess carbon dioxide in the atmosphere. The burning of fossil fuels and land use change, such as deforestation, are major contributors to the sharp rise in carbon dioxide emissions. As a result, the ocean absorbs a significant amount of this carbon dioxide, leading to a decrease in its pH level and an increase in acidity. This phenomenon, known as ocean acidification, has far-reaching consequences for marine life and humans who depend on it. It is a global threat, impacting every ocean and coastal estuary, and its effects are already being observed in various species, such as oysters, clams, and corals.

The burning of fossil fuels

At least one-quarter of the carbon dioxide released from burning these fossil fuels does not remain in the air but is absorbed by the ocean. Since the beginning of the industrial era, the ocean has absorbed approximately 525 billion tons of CO2 from the atmosphere, currently averaging around 22 million tons per day.

When carbon dioxide dissolves in seawater, it leads to ocean acidification, a process that lowers the pH of the seawater, making it more acidic. This chemical change in the ocean's composition has significant implications for marine life and, by extension, humans who depend on these ecosystems for food and economic activities.

Ocean acidification poses a particular challenge for shellfish and other calcifying organisms, including oysters, clams, lobsters, shrimp, and coral reefs. These organisms rely on carbonate ions to build and maintain their shells and skeletons. However, the increased acidity in seawater binds and reduces the availability of these ions, making it difficult for these organisms to survive and reproduce.

Additionally, the burning of fossil fuels has contributed to the rise in global temperatures. While the ocean's absorption of carbon dioxide has helped mitigate atmospheric CO2 levels, it has come at the cost of changing the ocean's chemistry. This altered chemistry has far-reaching consequences for marine ecosystems, including the potential decline of certain species and the disruption of the ocean's ability to store pollutants.

Carbon dioxide absorption

The air pollutant responsible for acidifying the ocean is carbon dioxide (CO2). The ocean absorbs CO2 from the atmosphere, a process known as ocean carbon uptake or the ocean carbon sink. This occurs because, as the atmospheric concentration of CO2 increases, more of it is dissolved in the surface water of the ocean.

The ocean has absorbed approximately 525 billion tons of CO2 from the atmosphere since the beginning of the industrial era, currently absorbing around 22 million tons per day. This amounts to about 40% of the carbon dioxide added to the atmosphere by fossil fuel burning. The ocean's absorption of CO2 has helped to slow the accumulation of atmospheric CO2 and, therefore, the pace of global warming.

However, this benefit has come at a cost. The increase in CO2 in the ocean alters the chemistry of seawater, a process known as ocean acidification. When carbon dioxide dissolves in seawater, the water becomes more acidic, and the ocean's pH drops. This has negative impacts on marine life, particularly shellfish and other calcifying organisms, as it makes building and maintaining shells and other calcium carbonate structures difficult.

Ocean acidification also affects other species vital to the marine ecosystem, including reef-building corals and pteropods (tiny snails eaten by several species, including fish and whales). It is weakening coral structures in the Caribbean and in cold-water reefs off the coasts of Scotland and Norway. It is also a concern for the Great Barrier Reef, where living corals have declined by half in the last three decades, reducing fish habitats and the resilience of the entire reef system.

The rate at which the ocean absorbs carbon dioxide can be influenced by human-caused changes to the atmosphere, such as the burning of fossil fuels, and natural events like volcanic eruptions. For example, the Pinatubo eruption in 1991 caused the ocean to absorb more carbon in 1992 and 1993, with the carbon sink slowly declining until 2001 when human activity began pumping more carbon dioxide into the atmosphere.

Marine life impact

Marine life is facing significant threats from air pollution, which is causing ocean acidification and eutrophication. Ocean acidification is a direct result of increased atmospheric carbon dioxide (CO2) from burning fossil fuels. The ocean absorbs CO2, leading to chemical reactions that increase acidity and decrease pH levels. This has a profound impact on marine organisms, particularly those that rely on calcium carbonate structures, such as shellfish and coral.

The increased acidity of the ocean makes it difficult for shellfish like oysters and clams to build and maintain their shells. It also weakens coral structures, reducing fish habitats and the resilience of entire reef systems. In addition, some harmful algal species produce more toxins and bloom faster in acidic waters, which can sicken fish and marine mammals and harm humans who consume contaminated shellfish.

Eutrophication is another consequence of air pollution, caused by the accumulation of nutrients in the water, often from excess nitrogen in rainwater. This stimulates excessive growth of plants and algae, leading to oxygen depletion when they die and decompose, creating "dead zones" where no organism can survive. Eutrophication can also amplify pH fluctuations, further exacerbating the effects of ocean acidification.

The impact of air pollution on marine life extends beyond shell-building organisms. Researchers study the effects of acidification on various life stages of different species, including their behaviour, energy use, immune response, and reproductive success. They have found that even if adult organisms can adapt, their young larvae may struggle. Additionally, some species of plants and algae may thrive under more acidic conditions due to increased carbon dioxide, but they are still vulnerable to other stressors like warming, pollution, and overfishing.

Overall, air pollution-induced ocean acidification and eutrophication pose severe threats to marine life, disrupting ecosystems and food chains that billions of people rely on for food and economic activities. These issues highlight the urgent need for effective air pollution control measures and sustainable development practices to protect our oceans and the life they sustain.

Human impact

Human activities, such as burning fossil fuels and changing land use practices, have significantly contributed to the increase in carbon dioxide (CO2) levels in the Earth's atmosphere. Since the beginning of the industrial era, the ocean has absorbed about 525 billion tons of CO2, currently absorbing around 22 million tons per day, which is about a third to half of all CO2 released by human activities. This absorption of CO2 by the oceans has led to a phenomenon known as ocean acidification, which poses a significant threat to marine life and human communities that depend on it.

Ocean acidification is the process by which carbon dioxide dissolves into seawater, forming carbonic acid, which then dissociates into bicarbonate and hydrogen ions, resulting in increased acidity and decreased pH levels. This change in the ocean's chemistry has direct consequences for marine organisms, particularly those that rely on carbonate ions to build and maintain their shells and skeletons, such as molluscs, corals, and some varieties of plankton. The shells of these organisms may become less dense and more fragile, making them more vulnerable to damage and dissolution.

Laboratory experiments have shown that under more acidic conditions, certain species of algae, plants, and seagrasses may actually thrive and reproduce better. However, in the wild, these organisms are also facing other stressors, such as warming waters, pollution, and overfishing, which may outweigh the potential benefits of increased CO2 levels. Additionally, the production of toxins by harmful algal species under acidic conditions can have detrimental effects on marine life, including fish, shellfish, and marine mammals, as well as humans who consume contaminated seafood.

The impacts of ocean acidification extend beyond the individual species level and have far-reaching consequences for marine ecosystems and human societies. For example, coral reefs provide essential protection to shorelines from storm surges and cyclones, sheltering habitable land for island nations. The degradation of these reefs due to acidification can lead to loss of life, property damage, and erosion, impacting tourism and the economies of coastal communities. Moreover, ocean acidification can disrupt marine food chains, affecting fisheries and the food supply for millions of people worldwide who rely on seafood as their primary source of protein.

The effects of ocean acidification are already being observed in various regions, including the Caribbean, the Great Barrier Reef, and the Antarctic. With continuing unabated CO2 emissions, the consequences are projected to worsen. By the end of the century, shellfish industries could face significant losses, and the ocean's capacity to absorb CO2 and regulate global warming may be severely compromised. Addressing the root causes of ocean acidification, such as reducing fossil fuel consumption and transitioning to more sustainable land use practices, is crucial to mitigating these impacts and preserving the health and balance of marine ecosystems.

Conservation efforts

Carbon dioxide (CO2) is the air pollutant that acidifies the ocean. The oceans absorb roughly a quarter of the CO2 released by human activities every year, resulting in a change to seawater chemistry known as ocean acidification.

The US Environmental Protection Agency (EPA) is working to address the pollutants that cause ocean and coastal acidification. These pollutants include carbon dioxide emissions, acid-rain-forming emissions, and nutrients. The EPA's Ocean and Coastal Acidification Program promotes awareness, conducts research, and monitors ocean acidification to develop solutions.

The EPA is also working to improve laboratory experiments to better match real-world ecology. This includes studying how seawater enriched with dissolved carbon dioxide and nutrients affects food chains, and how marine organisms respond to acidification, including the combined effects of acidification and oxygen depletion caused by nutrient pollution.

The EPA is collaborating with states and universities to study the impact of acidification on shellfish and coral reefs. They are developing computer models that predict changes in the ocean carbon cycle, water quality, and the social and economic impacts of ocean acidification.

The National Oceanic and Atmospheric Administration (NOAA) Ocean Acidification Program (OAP) works to prepare society for the consequences of ocean acidification and conserve marine ecosystems. This includes using models and research to understand the sensitivity of organisms and ecosystems to ocean acidification and make predictions about the future. OAP also focuses on developing innovative tools to monitor and mitigate changing ocean chemistry locally.

NOAA is also researching carbon dioxide removal (CDR) as a potential solution to ocean acidification. CDR aims to remove carbon dioxide from the atmosphere and store it on land, underground, or in the ocean. Voluntary carbon markets and private industry pilots are emerging as potential solutions, with NOAA serving as a trusted agency to monitor and evaluate these efforts.

Additionally, healthy forests can help reduce ocean acidification by absorbing CO2 from the atmosphere. Strategic forest management can enhance their capacity for carbon capture and storage. Thinning young forests can allow trees to grow larger, increasing their long-term carbon storage potential and promoting wildlife habitat.

Other conservation efforts include habitat restoration, engaging with local businesses and communities to mitigate excess CO2 emissions, and educating the public about ocean acidification through programs like aquarium outreach.

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