August 24, 2009
High Acidity Levels In Alaskan Waters
A marine scientist said Alaska's $4.6 billion fishing industry might be in danger because marine waters in the area are turning acidic from absorbing greenhouse gases faster than tropical waters, The Associated Press reported.
Jeremy Mathis, a chemical oceanographer at the University of Alaska Fairbanks, said the same things that make Alaska's marine waters among the most productive in the world - cold, shallow depths and abundant marine life "“ also make them the most vulnerable to acidification.
Global warming's effects on Alaska have already resulted in shrinking glaciers, coastal erosion, the march north of destructive forest beetles formerly held in check by cold winters, and melting Arctic Ocean ice that also threatens many marine mammals.
Increased carbon dioxide levels in the atmosphere are thought to create ocean acidification when basicity is lowered and the acidity of marine waters increases.
The Intergovernmental Oceanographic Commission shows that 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.
Carbonic acid forms when carbon dioxide dissolves in seawater, decreasing the amount of calcium carbonate, which is used by marine creatures to construct shells or skeletons.
Mathis reported that last spring he collected water in the Gulf of Alaska and found samples to be more acidic than expected - and higher than in tropical waters.
He noted that the results matched his findings in the Chukchi and Bering seas off Alaska's west and northwest coast.
Mathis uncovered multiple sites in the Gulf of Alaska 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. 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," he said.
Mathis explained that they are spending energy responding to acidity changes, and then that energy is diverted away from growth, foraging and reproduction.
He said a tiny pteropod, known as the sea butterfly or swimming sea snail, could also be affected by acidification. The seal snails make up nearly half of the diet of pink salmon and Mathis warned that a 10 percent decrease in pteropods could mean a 20 percent decrease in an adult salmon's body weight.
"This is a case where we see ocean acidification having an indirect effect on a commercially viable species by reducing its food supply," Mathis said.
Alaska's shallow waters around the broad continental shelves also retain more carbon dioxide since there is less mixing from deeper ocean waters.
However, the rich biological life of Alaska waters, from tiny plankton to humpback whales, are also contributing to acidification levels, as all use oxygen and emit CO2.
Experts call it the "biological pump."
Phytoplankton absorbs CO2 and gives off oxygen, but it decomposes and adds carbon to the water column when it dies and sinks in the shallow Alaska waters.
Fisheries managers have been reporting salmon returns with fewer, smaller fish reaching streams.
Mathis said they couldn't yet correlate that to ocean acidification or any climate process, but there are indications of stress in the ecosystem. He recommended a twofold course of action: increasing studies and observation of the effects of ocean acidification, and reducing carbon emissions.
After a review of Mathis' findings, the Center for Biological Diversity renewed its call for Alaska to declare its waters impaired under the Clean Water Act.
Last year, the state rejected the group's original request for the declaration.
On the Net:
- University of Alaska Fairbanks
- Intergovernmental Oceanographic Commission
- Center for Biological Diversity