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DIVE INTO SCIENCE

Chemistry Basics, 3 simple reactions:

Step #1: Every day, the ocean absorbs nearly a third of the carbon dioxide we put into the atmosphere from burning fossil fuels, driving cars, and clearing forests.

Step #2: When carbon dioxide dissolves into seawater it forms carbonic acid, and lowers the pH of seawater, making it more acidic.

Step #3: Rising acidity depletes seawater of carbonate ions, an essential ingredient used by creatures like shellfish and corals to build their shells.

What It Means

Changes in our oceans' chemistry are in motion. Around the world, oceans have become 30 percent more acidic, on average, since the Industrial Revolution. Many in the scientific community believe that this change is happening faster now than at any time over the past 300 million years. Scientists estimate that the acidity of our oceans could double or triple by the end of the century.

As carbonate becomes less available, corals and shelled animals must expend more energy to build shells and that leaves them less able to find food or reproduce. The resulting stress reduces their ability to survive and compete. If seawater becomes acidic enough, the animal's shell can dissolve.

But the impact can extend beyond marine creatures that build shells. In decreased pH in laboratory experiments, squid become lethargic, krill embryos fail to hatch, and reef fish get confused and are no longer able to detect predators. Finfish are also at risk because of changes in the food web. If shelled plankton at the bottom of the food chain start to struggle, commercially valuable finfish could have more trouble finding food.

The pH Factor

A pH unit is a measure of acidity ranging from 0-14. The lower the value is, the more acidic the environment. The ocean becoming more acidic means the pH is moving to a lower value. Pure water has a pH close to 7.

Seawater is not an acid because it measures above neutral on the pH scale. But adding carbon dioxide lowers the pH and causes it to shift towards the acidic end of the scale. Scientists refer to any change in that direction as "acidification," just as we may say a day is "warming" when snow starts to melt, even though it's still chilly outside.

Inside the Lab

photo of Paul McElhany

Paul McElhany in the lab

In a cramped NOAA laboratory in Seattle, researchers have begun to test how other valuable marine creatures will fare. With space so limited that the research equipment is encroaching on the parking lot, scientists are only able to run experiments on a few species at a time including oysters, geoduck, rockfish, crab, and tiny plankton that are important to the diets of the marine life you see at a local aquarium.

So far they and other labs in the region have run experiments on only about a dozen locally collected calcifying species. Yet there are an estimated 600 species throughout the Puget Sound that use calcium carbonate, which will become harder to produce in more acidic seas. This means we know little or nothing about how 98 percent of these calcifiers will respond.

It's even trickier to predict how changes may ripple across the food web. If sea urchins fare poorly, their overall numbers may not change much if predators like sea stars also decline. Fewer shrimplike creatures at the bottom of the food chain, such as copepods, could change the overall system much more dramatically than a decline in sea cucumbers, according to hypothetical modeling. Food web research underscores the importance of knowing which species will be most affected by ocean acidification.

"Everything suggests we're going to see changes and that there will be winners and losers," explains Paul McElhany, lead ocean acidification researcher for NOAA's Northwest Fisheries Science Center. He switched his focus from salmon restoration after realizing that habitat restoration projects may not matter anymore if the basic chemistry of the ocean changes. "It seems like a big enough problem that it could shuffle the entire ecosystem."

Learn more about the science:

U.S. Ocean Carbon and Biogeochemistry program FAQs
http://www.whoi.edu/OCB-OA/FAQs
NOAA: PMEL Carbon Program
http://www.pmel.noaa.gov/co2/story/Ocean+Acidification
NOAA Ocean Acidification Program
http://www.oceanacidification.noaa.gov
U.S. Ocean Carbon and Biogeochemistry program
http://www.whoi.edu/OCB-OA
Ocean Acidification International Coordination Centre
http://oceanacidification.wordpress.com
European Project on Ocean Acidification
http://www.epoca-project.eu/index.php/what-is-ocean-acidification/the-other-co2-problem-animation.html
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