Modeling the Pathways and Accumulation Patterns of Micro- and Macro-Plastics in the Mediterranean

The Mediterranean is considered a hot-spot for plastic pollution, due to its semi-enclosed nature and heavily populated coastal areas. In the present study, basin-scale coupled hydrodynamic/particle drift model was used track pathways fate of plastics from major land-based sources (coastal cities rivers), taking into account most important processes (advection, stokes drift, vertical horizontal mixing, sinking, wind drag, beaching). A hybrid ensemble Kalman filter algorithm implemented correct near- surface circulation, assimilating satellite data (sea height, temperature) in hydrodynamic model. Different size classes and/or types both micro- macroplastics were Biofouling induced sinking explicitly described, as possible mechanism microplastics removal surface. simplified parameterization size-dependent biofilm growth has been adopted, function bacterial biomass (obtained biogeochemical simulation), being proxy biofouling community. simulated distributions validated against available observations, showing reasonable agreement, terms magnitude variability. An 8-year simulation identify accumulation patterns layer, water column, seafloor beaches. impact different (vertical biofouling, wind/wave drift) identified through series sensitivity experiments. For macroplastics, at sea closely related adopted sources. concentration drastically reduced away source areas, with their distribution dominated by larger (>1 mm) open agreement observations. High patches floating convergence characterized anticyclonic circulation. on beaches followed predominant southeastward direction. sub-surface maximum abundance simulated, increasing contribution smaller particles deeper layers. Accumulation limited relatively shallow areas (<500 m), bottom depth below relaxation defouling. total amount (?3,760 tonnes) comparable estimates