Hydrodynamics of Mar Menor through field observations and numerical modeling: A wind-forced coastal lagoon

Coastal lagoons are ecologically critical yet highly vulnerable systems, with dynamics largely controlled by physical processes. The Mar Menor, Europe's largest hypersaline lagoon, has undergone marked ecological degradation, underscoring the need to understand its hydrodynamics and key forcing mechanisms. Here, we present a comprehensive assessment combining a year-long in situ observational dataset with high-resolution simulations using the Regional Ocean Modeling System (ROMS) implemented for the Mar Menor (ROMS-MarMenor-UPCT-H v1). Our results elucidate circulation patterns, highlighting the relative roles of meteorological and oceanic forcing, and provide essential insights for ecosystem management and restoration strategies in microtidal lagoons. Results show that astronomical tides from the adjacent Mediterranean Sea are strongly dampened within the lagoon, contributing minimally to sea level variance (<3%) and interior currents (<5%). Instead, atmospheric forcing dominates: the inverse barometer effect explains 37–51% of sea level variability, while wind drives up to 90% of current variance. Wind patterns generate a complex and dynamic circulation scheme, featuring three primary alongshore currents and multiple gyres, whose structure and rotation depend on wind direction. These patterns create a hydrodynamic division of the lagoon into northern and southern basins, with significant implications for particle retention and dispersion. Under northerly and southerly winds, the lagoon organizes into longitudinal circulation cells, featuring large-scale cyclonic or anticyclonic gyres in the central basin, often with vertical shear between surface and bottom layers flowing in opposite directions. In contrast, easterly and westerly winds induce a transverse subdivision, delineating distinct northern and southern basins separated by a frontal zone. These wind-driven conditions promote smaller-scale gyres, including one in the southernmost region and a persistent double-gyre system in the northernmost region. The resulting dynamically evolving flow structures strongly influence the retention of water, sediments, organic matter, and pollutants, highlighting the critical need for a detailed hydrodynamic characterization to inform sustainable management and support the lagoon's ecological restoration. • Comprehensive hydrodynamic assessment of Europe's largest hypersaline coastal lagoon. • Wind dominates (up to 90%) circulation inside the lagoon. • Wind direction creates distinct northern and southern basin divisions. • Complex gyre systems characterize the lagoon oceanographic structure.