The average pH levels in the world's oceans have dropped from 8.21 at the start of the Industrial Age (in the late 18th century) to an average 8.1 on the 1-to-14 scale, according to the IPCC. Changes will be more dramatic in coming years, the IPCC warns. Average pH levels are expected to decrease by as much as 0.4 by the end of the century, continuing the move in the acidic direction, the committee says.
Mathis and his fellow researchers are trying to understand how – and when – these changes might affect Alaska. They are making spring and fall voyages into the Bering Sea, Arctic Ocean, and Gulf of Alaska to analyze the contents of water retrieved from capsules plunged into the water column.
He cannot yet assign a specific average pH value to Alaskan waters, but other data show a clear trend line.
One indicator is the levels of calcium and aragonite. The minerals are fundamental to Alaska's offshore ecosystems. Shell-bearing animals such as king crabs and pteropods – small shell-encrusted creatures that make up the bulk of salmon's diet in the ocean – depend upon calcium carbonate.
In undersaturated zones, the calcium- and aragonite-poor water effectively robs those elements from the shells that sea creatures are trying to form. In general, the deeper the layer of saturation, the better for the fish.
Aragonite saturation in the Gulf of Alaska, of which Resurrection Bay is a part, has traditionally extended down to 250 meters, Mathis says. Calcium saturation in the gulf has reached down to about 500 meters, he says. But his data are showing that undersaturated waters are creeping up higher.
"The more man-made carbon dioxide we put into the ocean, the shallower those saturation points will become," says Mathis.
Effects of acidification are not obvious enough to be noticed by a casual observer.