Ananda Pascual (IMEDEA (UIB-CSIC), Spain); Diego Cortes-Morales (IMEDEA (UIB-CSIC), Spain); Maxime Ballarotta (CLS, France); Marie-Isabelle Pujol (CLS, France); Laura Fortunato (Università degli studi di Napoli Parthenope, Italy); Baptiste Mourre (IMEDEA (UIB-CSIC), Spain)

In this study we investigate the improvements in monitoring surface mesoscale activity in the western Mediterranean Sea enabled by the new wide-swath altimetry data from the SWOT mission. We compare the recently released high-resolution surface current product (MIOST v2.0.1 and previous versions), which integrates SWOT KaRIn observations during the 2023–2024 science phase, with the operational Copernicus Marine DUACS product (optimal interpolation method). Eddy fields are analyzed using an eddy identification and tracking algorithm, the py-eddy-tracker. We observe differences between the number of eddies identified, especially in coastal regions. The differences in eddy characteristics—such as radius, amplitude, and kinetic energy—are quantified by identifying eddies present in both datasets. To complement this Eulerian approach and to assess the practical implications of these differences, we conduct Lagrangian simulations using OceanParcels to evaluate the retention capacity of Algerian eddies and their role in transporting marine debris. This case study focused on the Cabrera National Park shows that including the SWOT KaRIn data affects the detection of mesoscale pathways relevant to pollution exposure. We quantify the differences in retention capacity of Algerian eddies identified in both fieldsets, observing significant differences in retention strengths, and even opposite effects (retention vs leakage). These findings help us to quantify the improvements provided by including the SWOT KaRIn data in gridded altimetric products. Moreover, this application highlights the added value of SWOT data for advancing operational ocean monitoring, with direct implications for marine conservation, pollution risk assessment, and sustainable maritime operations.