The northern European shelf as increasing net sink for CO2.

We developed a simple method to refine existing open ocean maps towards different coastal seas. Using a multi linear regression we produced monthly maps of surface ocean f CO₂ in the northern European coastal seas (North Sea, Baltic Sea, Norwegian Coast and in the Barents Sea) covering a time period from 1998 to 2016. A comparison with gridded SOCAT v5 data revealed standard deviations of the residuals 0 ± 26 μatm in the North Sea, 0 ± 16 μatm along the Norwegian Coast, 0 ± 19 μatm in the Barents Sea, and 2 ± 42 μatm in the Baltic Sea.We used these maps as basis to investigate trends in f CO₂, pH and air-sea CO₂ flux. The surface ocean f CO₂ trends are smaller than the atmospheric trend in most of the studied region. Only the western part of the North Sea is showing an increase in f CO₂ close to 2 μatm yr^-1, which is similar to the atmospheric trend. The Baltic Sea does not show a significant trend. Here, the variability was much larger than possibly observable trends. Consistently, the pH trends were smaller than expected for an increase of f CO₂ in pace with the rise of atmospheric CO₂ levels. The calculated air-sea CO₂ fluxes revealed that most regions were net sinks for CO₂. Only the southern North Sea and the Baltic Sea emitted CO₂ to the atmosphere. Especially in the northern regions the sink strength increased during the studied period. [ABSTRACT FROM AUTHOR]