As a (bad) joke, marine scientists have called ocean acidification the “other” global ocean problem, “The Other CO2 Problem,” or even climate change’s evil twin.
Don’t be fooled by this playful language though. Ocean acidification (OA) poses very serious biological and economic threats to marine ecosystems around the world. Unfortunately, compared to sea surface warming and sea level rise, OA has historically gone “under the radar” and until recently, most climate models underestimated the rate and severity of OA. In this blog, we explain the science behind this pervasive ocean problem and why it’s a challenge for New England’s waters.
Globally, oceans are acidifying 10x faster than they have in 300 million years. As a carbon sink, the ocean is supposed to sequester CO2 among other gases from the atmosphere, helping to regulate the greenhouse effect to an extent. In fact, a quarter of all carbon emissions end up in the ocean.
But in today’s world, where there is too much CO2 in the atmosphere, too much CO2 enters the ocean. Since the industrial revolution, human emissions have deposited over 530 billion tons of CO2 into the seas.
Before industrialization, the average ocean pH was 8.2, and today it is 8.1. While that may seem like a small difference, the –0.1 change in pH really means that the ocean contains 30% more hydrogen ions than it did just a few hundred years ago. Consequently, the blue planet’s chemistry is changing drastically.
A Chemical Double-Whammy
The reaction works something like this:
When CO2 mixes with seawater, it forms carbonic acid. Carbonic acid disassociates or breaks down into one hydrogen ion and one bicarbonate molecule. Bicarbonate then dissociates into two hydrogen ions and one carbonate molecule.
For every CO2 molecule that enters the ocean, three hydrogen ions are created. This creates two major problems for ocean life.
First: The more hydrogen ions a solution has, the more acidic it is. So when CO2 enters the ocean and undergoes this process, the water acidifies—hence, ocean acidification. Acidified seawater can weaken or even dissolve animals’ shells and bone structures. OA may also reduce survivorship in oysters, coral, and maybe even fish larvae.
Second: As the concentration of hydrogen ions increases, the water’s concentration of carbonate decreases. This is a problem because calcifying animals—such as clams, mussels, and lobsters—rely on carbonate to build their shells and bones. But excess hydrogen ions obstruct this process. When this occurs, organisms must devote more energy to acquiring carbonate, which means they have less energy for everything else. This added stress can impact growth rates and development.
Clayton Starr, TalkingFish, 3 October 2019. Article.