Confronting Ocean Acidification: Protecting the Diversity of Life Below Water

Writer: Y8 Siyu (April) Chung

We are acidifying the oceans 10 times faster than at any point in the last 300 million years. And yet, most people have never even heard of ocean acidification. Ocean Acidification is indubitably one of the quietly unfolding, yet most pressing environmental issues our planet faces today. As part of the United Nations Sustainable Development Goal 14.3, reducing ocean acidification is critical for preserving marine biodiversity, ensuring food security, and maintaining the health of our oceans. The oceans, long regarded as Earth’s natural carbon sink, are now beginning to show the consequences of absorbing too much carbon dioxide (CO2) — consequences that are slowly, but surely affecting our daily lives. Unlike oil spills or plastic pollution, ocean acidification isn’t something that can be seen clearly with the naked eye. Its change is subtle and silent, but the damage it causes is anything but. The seriousness of this issue is massive, around 25% of all the  CO2 released into the atmosphere being absorbed by the oceans, disrupting the oceans’ natural chemistry, and being the primary cause of ocean acidification.

Fig 1. Diagram showing the detailed process of the chemical reactions behind ocean acidification

When the CO2 released into the atmosphere dissolves in the ocean, it forms water (H2O) and carbonic acid (H2CO3), as shown in the equation below. [Shown in Fig 1]

CO2 (aq) + H2O → H2CO3

Carbonic acid, when present in seawater, dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-). As the hydrogen ion concentration of the water increases, the acidity increases as well.

H2CO3 → H+ + HCO3-

Additionally, the free hydrogen ion then produced from the above reaction combines with a dissolved carbonate ion (CO32-) to form another bicarbonate ion. This reaction makes less carbonate (CO32-) ions available in the seawater that marine organisms need to build their shells.

H+ + CO32- → HCO3-

Fig 2. Diagram showing the overall process of Ocean Acidification

Since the pre-industrial era, the ocean’s average pH has significantly dropped from 8.2 to 8.1. This may sound minimal, but because the pH scale is logarithmic, it represents a 30% increase in acidity — a dramatic chemical shift in less than two centuries. Organisms such as oysters, sea urchins, crabs, and clams depend on carbonate to create strong calcium carbonate structures, building hard shells or exoskeletons. However, the reaction makes less carbonate ions available in the seawater for these organisms, and when carbonate becomes scarce, their shells become weaker, thinner, and more prone to damage. This not only threatens individual species, but can also potentially disrupt entire ecosystems and food webs. [Woods Hole Oceanographic Institution, 2023] 

A study conducted by Northeastern University provides a relevant example of this, noting that while photosynthetic organisms like algae and seagrasses might temporarily benefit from increased CO2 levels, calcifying species suffer greatly. Some species show a parabolic growth pattern: their shell development initially increases, but quickly declines once acidity passes a certain threshold. [Shown in Fig 3] This irregular growth makes it extremely difficult for species to adapt.

Fig 3. Impact of Ocean Acidification on the shell growth of calcifying species

One of the most concerning real-world consequences of this is already being felt by the oyster farmers in the United States. On both coasts, mass die-offs of oyster larvae have been reported, as the larvae simply could not access enough carbonate to build their initial shells, leading to widespread failure in their reproduction and survival. This once had a devastating economic impact on the multi-million dollar industry, and it’s perhaps just one example of how ocean acidification can affect human lives.

A second case study, by Dr. Sindia M. Rivera-Jimenez of Santa Fe College, reinforces the scale of the threat. Her research notes that atmospheric CO2 concentrations are on track to double compared to pre-industrial levels by the year 2100. [Shown in Fig 4] If this happens, oceans will become more acidic than they’ve been at any point in the last several million years. For many marine species, this may mean a future they cannot survive through. [Rivera-Jimenez, Sindia M. ,N.D]

Fig 4. Data showing increase of recorded CO2 levels in the ocean

So what can be done? Multiple strategies have been suggested, but reducing fossil fuel emissions strongly remains the most fundamental yet powerful solution. This means transitioning to clean energy sources, improving energy efficiency, and reducing emissions from transportation, industry, and agriculture. By cutting CO2 emissions at the source, we essentially reduce the amount entering the ocean — and slow the pace of acidification. Other supportive methods include conserving energy, encouraging public transport, and investing in climate-friendly infrastructure. These strategies align with not only the prevention of ocean acidification, but also offer co-benefits such as improved air quality, and healthier communities.

However, these solutions come with notable challenges. Transitioning away from fossil fuels requires political will, international cooperation, and long-term investment. It also demands significant changes in consumer behavior and corporate accountability. While this may not be easy, it is an essential sacrifice for individuals to make in an attempt to dwindle the rapid change ocean acidification has and is making to the countless marine species living below the waves.

Ocean acidification can be seen as not only an ongoing problem our planet is facing, but also a clear reminder that the atmosphere and ocean are deeply connected. What we release without thought into the air doesn’t disappear as many people might confound — it dissolves into the water, changing the diversity of life beneath the surface. People commonly carry a misconception that the greenhouse gases we release only impact the atmosphere we see in our daily lives, but that is hardly the case. Reducing CO₂ emissions is not just about the climate and the atmosphere above — but also about protecting the marine life below.

Citations

Anderson, Kara. “Ocean Acidification: Causes, Issues and Solutions.” Greenly.earth, 24 Aug. 2024, greenly.earth/en-gb/blog/ecology-news/ocean-acidification-causes-issues-and-solutions. Accessed 1 May 2025

European Environment Agency. “Ocean Acidification.” Www.eea.europa.eu, 29 May 2024, www.eea.europa.eu/en/analysis/indicators/ocean-acidification. Accessed 1 May 2025

Hu, Shelia. “Ocean Acidification: What You Need to Know.” Www.nrdc.org, NRDC, 13 Oct. 2022, www.nrdc.org/stories/ocean-acidification-what-you-need-know. Accessed 1 May 2025

Marine Science Center, Northeastern University. Impact of Ocean Acidification on Marine Species. cos.northeastern.edu/wp-content/uploads/2018/06/Ocean-Acidification-Case-Study.pdf. Accessed 24 April 2025

NOAA. “What Is Ocean Acidification?” National Ocean Service, NOAA, 2024, oceanservice.noaa.gov/facts/acidification.html. Accessed 1 May 2025

“Ocean Acidification.” National Oceanic and Atmospheric Administration, U.S. Department of Commerce, 25 Feb. 2025, www.noaa.gov/education/resource-collections/ocean-coasts/ocean-acidification. Accessed 1 May 2025

Rivera-Jimenez, Sindia M. A Case Study on Ocean Acidification. www.sesync.org/sites/default/files/case-studies/Ocean%20Acidification%20Case%20Study%20%E2%80%93%20Student%20Handouts.pdf. Accessed 24 April 2025

Union of Concerned Scientists. “CO2 and Ocean Acidification: Causes, Impacts, Solutions.” Union of Concerned Scientists, 30 Jan. 2019, www.ucs.org/resources/co2-and-ocean-acidification. Accessed 1 May 2025

Woods Hole Oceanographic Institution. “Ocean Acidification.” Woods Hole Oceanographic Institution, 2023, www.whoi.edu/know-your-ocean/ocean-topics/how-the-ocean-works/ocean-chemistry/ocean-acidification/. Accessed 1 May 2025