Ocean Circulation Modulating the Nutrient Distribution and Fluxes at Regional and Fine Scales: A Case Study in the Northwestern Mediterranean Sea

Abstract In the oligotrophic ocean, nutrient distribution plays a key role in controlling primary production via upward fluxes. In spring 2023, the BioSWOT‐Med cruise investigated how fine‐scale ocean dynamics influence nutrient availability in the Mediterranean Sea. Combining SWOT satellite observations with targeted Lagrangian high‐resolution sampling, the study focused on a 50 km domain encompassing contrasting waters across the North Balearic Front and a fine‐scale anticyclonic eddy. Clear contrasts appeared in nutriclines depths and gradients and in nutrient diapycnal fluxes. Within the eddy, isopycnals and nutriclines were deepened and vertical nutrient gradients weakened, limiting local supply despite turbulence associated with near‐inertial waves. Nevertheless, along‐isopycnal gradients and lateral stirring generated nutrient transport from the eddy toward surrounding waters, the eddy acting counterintuitively as a nutrient relay. SWOT‐resolved fine‐scales reveal previously unresolved interactions between physical dynamics and nutrient availability, particularly important for biogeochemical and ecosystem functioning in oligotrophic regions.