9.7 Ocean Acidification

Dissolving CO2 in seawater increases the hydrogen ion (H+) concentration in the ocean and thus decreases ocean pH, as follows:

Ocean acidification is caused by the absorption of excess atmospheric CO2 into the ocean. As more CO2 is released into the atmosphere, the oceans will continue to become more acidic. Humans are inadvertently causing ocean acidification by increasing atmospheric CO2 with the burning of fossil fuels and deforestation. Over the last 200 years of global industrialization, ocean pH levels have dropped by 0.1 pH units. The pH scale is logarithmic, meaning that a change of 0.1 would translate to a 30% increase in ocean acidity levels. 🧪

As CO2 dissolves in seawater, it forms carbonic acid, which, in turn, reduces the pH of the water. This process can have a number of negative effects on marine life, including making it more difficult for organisms like corals, snails, clams, and shellfish to build and maintain their skeletons and shells. 🐚

Carbonic acid reduces available calcium carbonate in the ocean. Calcium carbonate is important for marine organisms because it provides a strong and durable material for building skeletons and shells. These structures are essential for protecting the organisms from predators and for maintaining their shape and buoyancy. Additionally, calcium carbonate is also used by many organisms to control their internal pH and regulate the number of calcium ions in their bodies.

Additionally, acidification can also alter the behavior and physiology of fish. Many fish use their sense of smell to locate food, find mates, and avoid predators. Acidification can disrupt the ability of fish to detect certain odors, making it more difficult for them to interact with stimuli in their external environment. 🐠

In contrast, ocean plants like seagrass and algae tend to thrive in a CO2-rich environment. These conditions, lack of adequate herbivores, and exploding plant growth could create hypoxic, eutrophicated environments. 

Scientists are predicting that at current CO2 production, ocean acidity could increase by over 100% in the next 100 years. This change would present a significant challenge to marine organisms and impact human populations that rely on them. 

One organism of concern is the pteropod. These tiny pelagic snails make up the basis of the food chain for a wide variety of animals. Scientists have studied these organisms in ocean waters that simulate predicted acidity levels, and their shells completely dissolve in less than 50 days! The collapse of this species would have a domino effect on the organisms that rely on it for food. Whales, salmon, and other pelagic organisms would most likely not survive the total collapse of pteropods. 🌀

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