Dr. Jeffrey Short recently retired from a 31-year career as a research chemist at NOAA, where he worked primarily on oil pollution and other contaminant issues. He was the leading chemist for the governments of Alaska and the United States for the natural resource damage assessment and restoration of Exxon Valdez oil spill, and guided numerous studies on the distribution, persistence and effects of the oil. Dr. Short is the author of more than 60 scientific publications and has contributed to 3 books. Dr. Short is now Pacific science director with Oceana.
Q. Can you explain in layman’s terms what ocean acidification is?
A. Some of the carbon dioxide added to the atmosphere from cars, factories and other human activities has dissolved into the ocean, where it reacts with seawater to form carbonic acid. This process is exactly the same as that used to make carbonated water, which is produced by mixing carbon dioxide gas with water, which makes the water quite acidic. Natural seawater is mildly alkaline, meaning it tends to neutralize acids, but as acid is added it weakens this neutralizing ability. This weakening results from depletion of chemicals in seawater that react with the acid. The most important of these chemicals is called carbonate ion, which are also important building blocks for shelled and reef-building organisms in the sea.
Within the last 20 years, scientists have discovered that over the course of the Industrial Revolution, enough carbonic acid has been added to decrease carbonate ions in seawater by about 17% on average in the surface layer of the ocean worldwide. Scientists estimate that if carbon dioxide continues to be added to the atmosphere at the current rate, carbonate ions could fall another 20% from the current level by the end of this century, with serious consequences for marine life.
Q. What are the effects of ocean acidification, and why are so many people worried about it?
A. The most obvious effects of ocean acidification are on reef-building corals and on organisms that make shells out of calcium carbonate, including lobsters, crab, shrimp, oysters, clams, mussels, and a host of other animals. Depletion of carbonate ions makes it more difficult for these organisms to build reefs or shells. The most vulnerable period is during the embryonic stage, when organisms need shells most for protection but have little energy to spare to build them under more difficult conditions.
Experiments with coral reef-building organisms indicate that they will not be able to keep up with natural erosion by about the middle of this century, when coral reefs will begin to irreversibly die out. But ocean acidification has many other more subtle effects on how the ocean functions too. It changes some of the forms of nitrogen available to nourish marine plants, which affects their growth and distribution. It affects the potency of marine toxins, making plants and animals more or less able to defend themselves. It increases the toxicity of many pollutants discharged into coastal marine waters. It alters the ability of at least some fish to orient themselves in the water column and to release their metabolically produced carbon dioxide (i.e. “exhale”), which may make them more vulnerable to predation. It even increases the efficiency of sound transmission in seawater, making the ocean noisier for sound-sensitive marine mammals.
Moreover, these changes are happening simultaneously and fast, making it difficult for marine life to adapt. The last time the ocean acidified was anywhere near as fast as it is today was at the end of the Paleocene era 54 million years ago, and it caused a biological mass extinction in the ocean then. That is why scientists are so concerned today about ocean acidification, because it has been known to fundamentally transform the character of the ocean by killing a large proportion of the species that live in it.
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