Ocean Blues Print
Written by Sandra Hines   
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Since the Industrial Revolution, Earth’s oceans have swallowed nearly half of all fossil-fuel carbon emissions. Damage could be reaching the tipping point, threatening the entire marine food web.

It can melt the shells of the tiny snails that, at times, make up half the diet of juvenile salmon, pollock, herring and cod in the North Pacific. It can halt the growth of the protective armor on microscopic plankton found in such abundance that they make the sea appears aqua blue from outer space.

It could help destroy Earth’s coral reefs—where a quarter of all the organisms in the ocean spend at least part of their lives, and which are a living resource for 300 million people.

“We’re talking about tiny marine plants and animals—that larger organisms depend on—being affected from the tropics to temperate and arctic waters. We can see this as a worldwide problem,” says Richard Feely, a University of Washington affiliate professor of oceanography.

Another doomsday scenario because of global warming? Not exactly.  While human-made carbon dioxide is the cause, Feely is not blaming higher temperatures alone for this nightmare. Instead he’s talking about ocean waters becoming more acidic, a process called ocean acidification.

Unlike climate change—which can reveal itself in varied ways, including making some places colder—ocean acidification is a straightforward response of seawater to excess carbon dioxide, says Oceanography Professor James Murray, the founding director of the University’s Program on Climate Change. While the debate continues on how much global warming is human-caused, there is no quarrel over changing ocean chemistry. Oceanographers agree that ocean acidification is the result of carbon dioxide generated since the Industrial Revolution. In the past 200 years, the oceans have absorbed about 525 billion tons of carbon dioxide from the atmosphere, nearly half of all fossil-fuel emissions.

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Threatened by rising levels of carbon dioxide in the oceans: white speckled hermit crab. Photo by Paige Gill.
If you can estimate how much excess carbon dioxide humans will put into the atmosphere in coming years, then scientists can tell you how much ocean acidification to expect. “The predictions point to a dire state of affairs,” Murray says. “The whole marine food web could be affected.”

As human-made carbon dioxide gas dissolves into seawater, it threatens the shells, protective coatings and skeletons of tiny organisms. These organisms use substances in the water to build and maintain their “armor and bones” in a process called calcification.  If the ocean chemistry changes enough, they can become weak and even shell-less.

In addition, larger organisms are in danger.  Oyster and mussel shells can thin. The latest work shows some types of crabs are also affected. Even organisms that don’t depend on calcification appear susceptible. Acidification of seawater triggers changes in the size of fish egg sacs and eggs, and causes mortality rates of 60 percent to 80 percent in a variety of fish species when they are in their vulnerable larval form.

At present, the chemistry of the oceans is changing at least 100 times more rapidly than it has during the 650,000 years preceding our industrial era, wrote Feely and colleagues last year. “If current carbon dioxide emission trends continue, computer models show that the ocean will continue to undergo acidification to an extent and at rates that have not occurred for tens of millions of years.”

Haven’t heard about ocean acidification? You’re not alone.