Ocean acidification has an effect on the on the formation of shells and skeleton of organisms. Photo: Peter Leopold, Norwegian Polar Institute

Rationale: The ocean has taken up between 30 to 50% of the human induced CO₂. This has led to a pH decrease and a decrease in carbonate ion concentration ([CO₃^-2]). There is a large natural seasonal and interannual variability. Long-term monitoring is required to discern the change due to increased CO₂ and its impact on OA state