Corals Hit an Acid Note - Sailors for the Sea

Corals Hit an Acid Note

By: Christopher Langdon, Ph.D., associate professor, University of Miami Rosenstiel School of Marine and Atmospheric Science | January 1, 2010

This is the first of three essays on coral reefs and climate change.

Oceans play a vital role in the Earth’s climate system by regulating the amount of carbon dioxide in our atmosphere.

Over hundreds of thousands, or even millions of years, oceans slowly release carbon dioxide to the atmosphere through underwater volcanic emissions and absorb it again as carbonate sediments dissolve over a long period of time. However, on shorter time scales, say only a few hundred years, the atmosphere can handily drive the carbon dioxide content of the ocean. This happens when the gas content of the atmosphere is out of balance with the oceans, much like it is becoming right now. 

The massive and rapid release of carbon dioxide into the atmosphere due to the burning of fossil fuels and deforestation has knocked the Earth’s carbon cycle out of balance. As nature struggles to restore balance, oceans are absorbing an alarming two Giga-tons of carbon, or nearly one metric ton of the carbon dioxide per person, per year. At this rate, the planet’s natural processes cannot keep pace with human carbon dioxide emissions.

Thirty percent of the total global carbon dioxide emissions since the year 1800 (about 118 billion metric tons!) have been absorbed by the ocean through a slow chemical exchange between the atmosphere and sea surface. Despite the huge size of our oceans, this accumulation is gradually lowering the pH level of the ocean’s waters, making water more acidic, and making it more difficult for corals and other important marine organisms to survive. 

In the Lab

A couple of years ago, my colleague coral reef biologist Dr. Andrew Baker and I established a laboratory specifically testing what life in the ocean might be like for animals years from now. As a chemical oceanographer I am interested in how corals respond to the combined stress of global warming and ocean acidification; two threats considered imminent in today’s climate change debate. 

In our lab, live coral fragments are placed in tanks under precisely controlled temperatures, natural light and carbon dioxide conditions, which mimic some of the environmental factors naturally occurring in the Florida Keys. 

Our research is showing that a coral’s ability to produce their limestone skeletons decreases as waters become more acidic, a conclusion which suggests that these fragile underwater organisms will grow at a slower rate, or their skeletons will become more fragile — a process that can be compared to osteoporosis in human beings. As a result, reef formations will become increasingly brittle and unable to build protective structures to shield us from hurricanes and other natural phenomena because erosion will wear them away faster that they can grow. 

Through our research, we are hoping to find ways in which to better understand, and even lessen the impact ocean acidification will have on our important marine ecosystems.

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