Saturday, September 12, 2009

Global Warming Threatens Alaska's Waters With Acidification

By Dan Joling, Christian Science Monitor. Posted September 9, 2009.

Alaska's marine waters are turning acidic from absorption of greenhouse gases faster than tropical waters.

Erosion threatens to topple coastal Alaska villages. Melting ice threatens polar bears. Now, a marine scientist says the state's marine waters are turning acidic from absorbing greenhouse gases faster than tropical waters, potentially endangering Alaska's $4.6 billion fishing industry.

The same things that make Alaska's marine waters among the most productive in the world -- cold, shallow depths and abundant marine life -- make them the most vulnerable to acidification, says Jeremy Mathis, a chemical oceanographer at the University of Alaska Fairbanks.

"Ecosystems in Alaska are going to take a hit from ocean acidification," he says. "Right now, we don't know how they are going to respond."

Alaska has already seen more than its share of global warming effects: shrinking glaciers, coastal erosion, the march north of destructive forest beetles formerly held in check by cold winters, melting Arctic Ocean ice that also threatens walrus and other marine mammals.

Ocean acidification, the lowering of basicity and the increase in acidity of marine waters, is tied to increased carbon dioxide levels in the atmosphere.

Oceans absorb 22 million tons of carbon dioxide from human activities per day, removing 30 percent emitted to the atmosphere each year and mitigating the harmful impact of greenhouse gas, according to the Intergovernmental Oceanographic Commission.

When carbon dioxide dissolves in sea water, it forms carbonic acid. That decreases the amount of calcium carbonate, used by marine creatures to construct shells or skeletons.

Mathis last spring collected water in the Gulf of Alaska and found samples to be more acidic than expected -- and higher than in tropical waters. The results matched his findings in the Chukchi and Bering seas off Alaska's west and northwest coast. Cold water absorbs and holds more gas than warm water, Mathis says.

His research in the Gulf of Alaska uncovered multiple sites where concentrations of shell-building minerals were so low, that shellfish, including crab, and other organisms would be unable to build strong shells.

"We're not saying that crab shells are going to start dissolving, but these organisms have adapted their physiology to a certain range of acidity," Mathis says. "Early results have shown that when some species of crabs and fish are exposed to more acidic water, certain stress hormones increase and their metabolism slows down.

"If they are spending energy responding to acidity changes, then that energy is diverted away from growth, foraging and reproduction."

Acidification could affect the tiny pteropod, also known as a sea butterfly or swimming sea snail. It is at the base of the food chain and makes up nearly half of the diet of pink salmon. A 10 percent decrease in pteropods could mean a 20 percent decrease in an adult salmon's body weight.

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