Eddy-induced chlorophyll variability in the Norwegian Sea revealed by Bio-Argo observations

Mesoscale eddies play a vital role in shaping marine biogeochemical processes, particularly influencing chlorophyll (Chl) distribution in oceanic systems. Understanding how eddies affect Chl distribution is critical for assessing regional productivity. The presented study focuses on the Norwegian Sea region, which is characterized by the high intensity of mesoscale eddy activity and complex dynamical processes. To study the eddy impact on the Chl distribution in the region of interest, we employed a colocalization method that combines altimetry data with Bio-Argo profiles, allowing us to derive composite Chl structures for both cyclonic (CEs) and anticyclonic (AEs) eddies. Our study provides insights into the subsurface 2D and 3D patterns of eddy-induced Chl distribution, showing that both CEs and AEs can enhance Chl concentration in the Norwegian Sea, with AEs driving greater Chl elevation during the summer months. Our analysis reveals that both eddy types are associated with positive subsurface Chl anomalies, reaching up to 0.5–0.7 mg/m³, with the strongest signals confined to the upper 50 m. While CEs exhibit peak anomalies near 25 m depth, AEs show a more complex dipole-like structure with maxima located both in the core and at the periphery within a depth layer of ∼20–50 m. The obtained results also demonstrated remarkably high concentration of Chl within the Lofoten Vortex. Given the prevalence of mesoscale eddies in the region, these findings suggest their crucial role in the biogeochemical dynamics of the Norwegian Sea.