World Oceans Day & Ocean Acidification

June 8 is World Oceans Day and the theme this year is Healthy oceans, healthy planet. Oceans cover 71% of the earth’s surface and have a huge capacity to store heat, playing a critical role in the climate system. In addition to that role, oceans are a complex and rich ecosystem on their own — helping to sustain life on land. But there are many threats to the viability of the oceans. One of them is acidification.

Ocean acidification may not be the first thing that comes to mind when you think about impacts of more CO2 in the atmosphere. But currently, oceans absorb about a quarter of the CO2 humans produce every year. All gases in the atmosphere interact with seawater, but when CO2 mixes with the water, it forms carbonic acid. Increased carbonic acid leads to the depletion of carbonate ions, which are an essential component of minerals vital for building sea shells.

Acidity is measured on the pH scale, where 0 is most acidic, 7 is neutral, and 14 is most basic (a base is the opposite of an acid). Since the industrial revolution, the ocean pH has dropped from 8.2 to 8.1. While that does not sound like much, that's a 30% increase in acidity. Each digit on the scale indicates a change by a factor of 10. So, a pH of 7 is 10 times more acidic than an 8. At current emission rates, ocean pH may drop to 7.8 by the end of the century, creating an ocean more acidic than any seen in the past 100 million years.

The current rate in acidity change is about 50 times faster than any known historical change, making it difficult for marine life to adapt. Carbonate ions in the ocean become less abundant in a more acidic ocean, making it difficult for shellfish (clams, oysters, mussels) to build shells and skeletons. Additionally, smaller organisms, called plankton, which form the base of the oceanic food web, also have trouble adapting.

In a cascading effect, this will alter ecosystems in a way that could threaten seafood staples around the world. More than 1 billion people rely on oceans for food, and the jobs and economies in coastal communities in the U.S. depend on fish and shellfish. A report from the Convention for Biological Diversity estimates ocean acidification will cost the global economy $1 trillion annually by 2100.

Corals are threatened in a similar way. With less calcium carbonate available in a more acidic ocean, it hinders the ability for corals to maintain their reefs, which are important habitats for other marine organisms and provide some coastal protection from storms. Some research suggests that by the end of the century, reefs may erode faster than they can be rebuilt.