Not only do oceans provide food, habitat, and places to swim and sail, but they also help control the Earth’s climate, acting as giant sponges for our carbon dioxide emissions. You might think “Wow, that’s a great way to get rid of all the extra greenhouse gases we’re producing!”, but too much CO2 can lower the pH of the ocean, making the oceans more acidic. This series of chemical reactions, called ocean acidification, can be harmful to coral reef formation and to shell-building organisms like clams and crabs.
Watch this short video to learn the chemistry behind ocean acidification.
Analyzing data collected from ocean transects and fixed buoy stations, scientists calculate that Earth’s oceans absorb 25% of all CO2 emitted annually (1). Over the past 250 years, 560 billion tons of CO2 has been absorbed. During this same time period, the pH of the world’s oceans has fallen from 8.2 to 8.1 (1). While a 0.1 difference doesn’t sound very significant, it translates to a 30% change in pH over a relatively short time scale (2).
Source: The Center for Microbial Oceanography: Research and Education (C-MORE), an NSF Science and Technology Center (EF-0424599).
Let’s look at some data on changes in Hawaii’s air and ocean chemistry to help demonstrate the relationship between carbon dioxide and ocean acidification. In the graphs to the right, the top graph compares concentrations of carbon dioxide (CO2) measured in the atmosphere at the Mauna Loa Observatory (red) against CO2 measured offshore in seawater (blue). Both sets of data show an increase in CO2 concentrations over the past 25 years. The bottom graph shows a downward trend in in ocean pH over the same timeframe. As more CO2 is absorbed by the ocean, the pH becomes lower. Over the past 25 years, the pH of ocean waters near Hawaii has become more acidic.
Much like the other indicators of climate change, there are regional differences, or “hotspots” of ocean acidification. Coastal upwelling in the Pacific Ocean, urbanization of coastal areas, and changes in sea ice extent can affect the rate at which acidification occurs and also the extent of the impacts to marine life and the coastal economy (1).