Variability and response of surface chlorophyll to the marine heatwave in the southern North Sea

This study investigates the variability and response of surface chlorophyll (CHL) concentrations in the southern North Sea to marine heatwaves (MHWs) over 26 years (1998-2023). The analysis uses daily high-resolution cloud-free SST and CHL data obtained from CMEMS. The SST showed a significant positive temporal trend, while the CHL concentration showed a non significant trend. Spatially, the CHL trend map showed high variability, with significant negative trends along the French coast and in certain regions west of the Dogger Bank and significant positive trends along the east coast of the United Kingdom, the Belgian and Dutch coasts, and the German Bight. The analysis of MHW and low chlorophyll (LCHL) events showed an increasing trend in the total number of MHW and LCHL days as well as compound MHW-LCHL days over the study period.