Oxygen concentrations in European coastal and marine waters

Description

Widespread oxygen depletion, partly due to natural conditions (stratification), occurs in the Baltic Sea and the Black Sea.
In the Baltic Sea, oxygen concentrations in the water layer near the sea floor decreased during the period 1990-2017 at 11 % of stations.
In the Greater North Sea area, decreases in oxygen concentrations during the period 1990-2017 were observed at 9 % of stations, mainly in fjords in Denmark and along the Norwegian and Swedish Coasts and at some stations in the German Bight.
Limited data were available for the Celtic Seas and the Adriatic Sea. Data coverage is not sufficient in all regional seas; it is sufficient for the Baltic and the North Seas, while data for only coastal waters are available for the Adriatic and Black Seas.
Reduced oxygen concentrations were observed at some stations in the coastal waters of the Black Sea, but there were no significant trends in oxygen concentrations during the period 1990-2017.
No significant trends in concentrations were observed for the majority of stations in all regions during the period 1990-2017.
The primary cause of oxygen depletion is nutrient input from agricultural fertilisers, causing eutrophication. The effects of eutrophication are exacerbated by climate change, in particular increases in sea temperature and in water-column stratification.