Reduced Ocean Carbon Sink in the South and Central North Sea (2014–2018) Revealed From FerryBox Observations

Surface seawater carbon dioxide partial pressure ( p CO 2 ) in the south‐central North Sea was measured between 2014 and 2018 using FerryBox‐integrated membrane sensors on ships‐of‐opportunity. Average annual p CO 2 variability was biologically controlled, with thermal effects modulating its amplitude. Deseasonalized winter trends of seawater p CO 2 were positive (4.4 ± 2.0–8.4 ± 2.9 µatm yr −1 ), biogeochemically driven, stronger than the atmospheric p CO 2 trend, and more pronounced than previous analyses. The trends calculated including all deseasonalized monthly averages were even higher (9.7 ± 2.8–12.2 ± 1.4 µatm yr −1 ). During our investigation, the southern study area became a stronger source and the northern part became a weaker sink for atmospheric carbon. Overall, average sea‐air CO 2 flux in our study area, from the Skagerrak to the Southern Bight (53°N), changed from −0.75 ± 0.61 mmol m −2  day −1 in 2014 to +0.20 ± 0.96 mmol m −2  day −1 in 2018.