Using dynamic ocean color provinces to elucidate drivers of North Sea hydrography and ecology

Ocean biogeochemical provinces have historically been used to characterize regions of similar biogeography, allowing for large-scale comparisons and the definition of possible management units. Recent studies have shown that ocean color (OC) may be used as a proxy for a range of physical and biological parameters, allowing for a more direct approach in defining and monitoring provinces. The current work investigates whether OC-derived provinces (area of a given OC type) can be identified in the North Sea and if they can provide insight into the system's dynamics. The analysis workflow was organized into three main steps: 1. OC type classification based on clustering of normalized reflectance spectra, 2. OC type characterization following match-ups to other biological and physical covariates, and 3. Exploration of drivers of OC province dynamics. Based on data from 1997–2019, four main OC types were identified, which are shown to be related to bio-optical, physical, and zooplankton community covariates. Atlantic-associated OC types varied in their coverage of the North Sea on seasonal and interannual scales, with increased penetration related to periods of a weakened circulation. Interannual variability of OC province extent was also found to correlate with an index of the Subpolar Gyre. These results indicate that the dynamics of OC provinces in the North Sea are likely driven by the interaction between large-scale circulation and local wind-driven and baroclinic currents. The perspective offered by OC provinces helps elucidate spatiotemporal patterns of plankton and is proposed as a novel operational index for additional exploration of ecosystem functioning.