Acidification in the Arctic Ocean is anticipated to be worse than previously expected due to a greater uptake of carbon dioxide (CO₂), new research suggests. This increase in CO₂ causes the frigid northern waters to become more acidic, which can ultimately lead to the decay of hard-shelled marine animals like mussels and “sea butterflies”.

Seawater absorbs atmospheric CO₂ as part of the natural climate cycle and sparks a series of chemical reactions that reduces the pH of seawater and carbonate ion concentrations, according to the NOAA Carbon Program. Mollusks, corals, and crustaceans pull these carbonate ions from the seawater in order to create their hard shells, but decreasing levels mean their shells will become weaker over time and, as they play a pivotal role at the base of the marine food chain, can have dire consequences for species of all predation levels.

In the Arctic Ocean, acidification is expected to have the greatest impact, finds research published in Nature. To come to their conclusions, researchers from the University of Bern employed current climate models to simulate how Arctic deep-water formation and “carbon inventory” will change based on models of surface water.

Greater regional anthropogenic carbon storage and ocean acidification are expected to get worse, and more so than previously expected. The Arctic Ocean will take up 20 percent more CO₂ over the 21st century than previously thought if atmospheric CO₂ continues to rise. This will lead to a decline in calcite by the end of the century that, when combined with “with rapidly changing physical and biogeochemical Arctic conditions, is likely to exacerbate the impact of climate change on vulnerable Arctic marine ecosystems,” the authors write.

"This leads to substantially enhanced ocean acidification, particularly between 200 and 1,000 meters", explains Jens Terhaar, a member of the group for ocean modeling at the Oeschger-Centre for Climate Change Research at the University of Bern in a statement. This can have important implications up the Arctic food chain and the larger fish and marine mammals that rely on calcium carbonate animals.

Pteropods are a key indicator of the effects of ocean acidification on calcite species. These “sea butterflies” are eaten by a number of predators of varying sizes, from krill to whales. Previous research published by NOAA found that the shells of pteropods dissolve over the course of just 45 days when “placed in seawater with pH and carbonate levels projected for the year 2100.”

The researchers conclude that the findings have “major implications” for sensitive Arctic marine ecosystems already made vulnerable by the effects of climate change and human impact. Available habitat for keystone species like pteropods (Limacina helicina) is likely to continue declining, affecting all levels of pelagic food webs while increased acidification is expected to “negatively affect the growth, survival, and behavior” of ecologically important species that rely on pteropods for food.