Ocean Acidifcation, Climate’s Step Sister

Until recently, ocean acidification was the quiet step-child lurking in the corner of the climate crisis. Earlier this month, the Expert Panel on Ocean Acidification, organized by the UN Department of Economic and Social Affairs, the UN Division for Ocean Affairs and the Law of the Sea, and the UN Foundation, met at UN Headquarters, to bring to light some of the affects of ocean acidification on marine life and ecosystems.

But now that it’s out of the shadows, scientists see the situation as more dire than they once thought.

Change in sea surface pH caused by anthropogenic CO2 between the 1700s and the 1990s
Credit: Wikipedia Commons

Ocean acidification – the lowering of the pH of the world’s oceans – has been taking place for decades. The National Oceanic and Atmospheric Administration (NOAA) reports that the oceans have absorbed about 50% of the CO2 released from the burning of fossil fuels. The excess CO2 reacts with hydrogen in water molecules, (H2O) to form hydrogen ions. Concentration of dissolved hydrogen ions determines how acidic the water is. Since the start of the Industrial Revolution, the astronomical increase in our appetite for fossil fuels has caused the acidity of the oceans to increase by about 30%.

Dr. J. Timothy Wootton, a professor in the Department of Ecology & Evolution at The University of Chicago began studying the ecological impacts of ocean acidification using data collected at Tatoosh Island, a group of small islands off the coast of Washington’s Olympic Peninsula over eight years ago. He and his colleagues collected data on pH, salinity, and temperature. Their results were disturbing.

“pH declines were occurring at a much faster rate than we expected,” said Dr. Wootton. The rate of decline of pH was more than an order of magnitude higher than the simulation models for the area had predicted – that is, the ocean around Tatoosh Island was become acidic ten times faster than hypothesized.

But the effects of pH decline are more subtle than the astronomical rate of change might suggest.

In a research paper published in 2008 by the National Academy of Sciences (NAS), Dr. Wootton noted that there is a “web of species interactions” that makes the ecological response to increased acidity far more complex than summary observation describes. His data showed a decrease in populations of two species of mussel, as well as in the abundance of a barnacle species. In contrast, the population of a second barnacle species, the acorn barnacle, and fleshy algae increased. In the Tatoosh Island ecosystem, Dr. Wootton and his and his colleagues observed that the pattern of species replacement changed in response to decreasing pH. Algae actually benefited. And algae remove CO2 from the atmosphere through photosynthesis.

“The emphasis has been on species with calciferous skeletons, exoskeletons,” said Dr. Wootton. “In truth, ecosystem response to changing pH is neither a simple function of having a certain kind of shell, or of decline in organism performance.”

We’d like solutions to complex problems to be simple. Often they aren’t. The overall effect on marine life of changing pH will have far-reaching consequences for the ocean ecosystem.