Mean surface seawater acidity

This indicator shows the yearly mean concentration of hydrogen ions in surface seawater in the northeastern Atlantic and adjacent seas, expressed in nanomoles per litre (nmol/l). An increase in the concentration of hydrogen ions corresponds to a decline in pH value and an increase in seawater acidity. This trend is caused by an increase in atmospheric carbon dioxide (CO2) concentrations, which increases the uptake of CO2 by the ocean. The Copernicus Marine Service has reconstructed the trends in global ocean acidification from 1985 onwards.