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.
"This is a case where we see ocean acidification having an indirect effect on a commercially viable species by reducing its food supply," Mathis says.
The shallow waters of Alaska's broad continental shelves also retain more carbon dioxide because there is less mixing from deeper ocean waters.
Another contributor is the rich biological life of Alaska waters, from tiny plankton to humpback whales. All use oxygen and emit CO2. Mathis and other scientists call it the "biological pump." Phytoplankton, like other plant life, absorbs CO2 and gives off oxygen, but when it dies and sinks in the shallow Alaska waters, decomposes and adds carbon to the water column.
Mathis has been warning fisheries managers around the state of ocean acidification. He has been hearing back of salmon returns with fewer, smaller fish reaching streams.