Ocean acidification is the term used to describe the long-term lowering of average global ocean pH. As concentrations of atmospheric carbon dioxide (CO2) increase, some of this CO2 is absorbed by the ocean. This triggers a series of chemical reactions that ultimately lead to lower pH and decreased concentration of carbonate ions in the oceans.
Since the Industrial Revolution, the average pH of surface ocean waters has decreased by 0.11 units, from 8.21 to 8.10. This may not seem significant, but the pH scale is logarithmic, meaning a decrease of a single pH unit represents a tenfold increase in acidity. The 0.1 drop in pH that we have seen corresponds to a 30% increase in ocean acidity.
The chemistry of ocean acidification is accepted and well understood by the scientific community. However, the biological impacts of ocean acidification on marine organisms and ecosystems are much more uncertain. A great deal of research is now being directed at understanding ocean acidification and its current and potential effects all over the world, including Alaska.
How will Alaska be affected by ocean acidification?
Alaska’s coastal waters are especially susceptible to ocean acidification compared to lower latitude oceans. First, cold water can absorb more CO2 than warm water, so our cold northern waters tend to be naturally high in CO2. This means that Alaska and other high latitude seas will likely see the effects of ocean acidification sooner than areas farther south. Additionally, natural factors such as high productivity, glacial melt, and upwelling increase the potential for regions around Alaska to be vulnerable to ocean acidification.
Alaska experiences large surface blooms of phytoplankton each year. Phytoplankton consumes CO2 through photosynthesis. When phytoplankton individuals die, they sink to the ocean floor and are decomposed by bacteria, which releases CO2 and lowers pH in the deep ocean.
In some parts of Alaska, deep CO2-rich water is churned up onto coastlines by natural, wind-driven upwelling. This upwelling mixes with the surface waters and lowers pH at the surface.
Glacier melt produces very dilute freshwater, and has low concentrations of the carbonate that helps the ocean buffer against lower pH. In the summer months when glacier melt is high, the surface waters of the ocean have a weaker buffer to changes in pH. This makes it easier for CO2 to decrease pH levels in the surface of the ocean.
A number of natural factors can influence sensitivity to ocean acidification in Alaska’s seas at different depths and at different times of the year. Ocean acidification is not uniform, and the range and degree of its impact can vary.