By: Ashley Hill
Ocean acidification is a hefty buzz word in the marine science community. It was coined in 2003 by two climatologists and since then scientists have recognized its negative effects on corals, shellfish, and even plankton. Ocean acidification, or OA, is a direct result of increased amounts of carbon dioxide in the atmosphere. The change in seawater chemistry becomes more noticeable as we continue to use fossil fuels. Let’s delve into exactly what’s happening and why it is a problem! Consider solutions to this problem as you read, it’s challenging!
1. Ocean acidification is a simple chemical change occurring in the ocean as a result of carbon emissions from the atmosphere. When carbon dioxide dissolves in seawater, it combines with the existing water molecules and carbonate ions. Through this reaction, two bicarbonate ions are created—binding up carbonate ions (this is bad, you’ll see why as you read). This continuous reaction in the ocean causes a reduction in pH, carbonate ions, and the saturation states of calcium carbonate minerals. Essentially the ocean becomes more acidic, there are fewer essential building blocks for calcareous (or calcifying) organisms, and the maximum amount of building blocks for those organisms in ocean is lowered.
2. Increased ocean acidity is a BIG problem. Before the Industrial Revolution (beginning in the early 1700s), the oceanic pH was 8.2. Since then, the pH has dropped to 8.1. Generally, anything with a pH of 7 or lower is considered acidic—so the ocean is becoming more acidic as the pH drops. Small changes in the pH of the ocean can have a negative impact on organism growth, reproduction, and crucial chemical communication because the changes are logarithmic—basically, pH 4 is 10 times more acidic than pH 5, and pH 4 is 100 times more acidic than pH 6. So WHY is this a big problem? As the ocean becomes more acidic, it affects calcifying organisms. Remember the carbonate in the reaction above, how the carbonate ions are getting bound up? Calcifying organisms use the carbonate ions along with calcium to create their calcium carbonate shells (or skeletons).
3. The resulting biological effects of ocean acidification are serious. The biological impacts of ocean acidification are not completely understood at this point because it is a relatively new area of study. Previously, scientists thought oceans taking in carbon dioxide was okay…this meant less carbon dioxide in the atmosphere, which was a good thing. Now, though, they are seeing the biological effects on the creatures in the ocean.
- Corals need calcium carbonate to build their homes, the coral reef structures we are all familiar with (and are actively restoring). The increased acidity and lowered availability of carbonate ions make it hard for corals to build their structures and maintain the existing structure.
- Other shelled animals, like mussels and oysters, have trouble building shells—this is a problem for their larvae too; the larvae have problems building their shells right from the start.
- Zooplankton that have calcareous structures are also at risk in acidic seawater. Plankton play a critical role in the oceanic food web, they provide nutrition for nearly all larger sea life, whether directly or indirectly. They also contribute to carbon cycling, an important aspect for all ecosystems.
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