The ocean's pH is dropping, and it is not a slow process.
In short: Often called the 'evil twin' of climate change, ocean acidification is a chemical shift driven by rising carbon dioxide. As the water becomes more acidic, it disrupts the very building blocks of marine life, threatening species that rely on calcium carbonate to survive.
Ocean acidification is a reduction in the pH of seawater, a process driven primarily by the absorption of atmospheric carbon dioxide. Over millions of years, seawater stayed mildly alkaline, averaging a pH of roughly 8.2. However, since the Industrial Revolution in the 1800s, the burning of fossil fuels and processes like deforestation have caused atmospheric CO2 to climb from 280 parts per million (ppm) to nearly 400 ppm today.
This chemical shift has profound biological consequences. When CO2 dissolves in seawater, it lowers the pH, making the water more acidic. This process interferes with the ability of marine organisms to form calcium carbonate, which is essential for building shells and exoskeletons. Vulnerable species include sea urchins, clams, oysters, and sea snails. Interestingly, research by Justin Ries and colleagues suggests that responses vary; while some species like conchs (Strombus alatus) deteriorate, others surprisingly thrive under higher CO2 concentrations.
The scale of this change is rapid. Although the ocean's pH has only dropped from 8.2 to 8.1, this represents a 25% increase in acidity over the last two centuries. Scientists note that the current rate of acidification is occurring faster than changes seen in the last 20 million years. While the ocean currently absorbs about one quarter of human-emitted CO2, the impact is felt unevenly, with half of this anthropogenic CO2 concentrated in the upper 400 meters of the water column.
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Sources
- Summary by Intellect · source: Ocean acidification | Biodiversity and human impacts | High school biology | Khan Academy
- Also: Ocean Acidification
- Also: What is ocean acidification? | Natural History Museum
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