Reduced Ocean Carbon Sink in the South and Central North Sea (2014–2018) Revealed From FerryBox Observations
Vlad A. Macovei, Wilhelm Petersen, Holger Brix, Yoana G. Voynova
Abstract
Abstract 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.