Assessing the microplastic retention in mesoscale eddies south of the Canary Islands

Abstract

Marine microplastic pollution is a growing environmental concern, yet little is known about its distribution in the water column and the role of mesoscale processes in shaping it. This study investigates the capacity of mesoscale eddies in the Canary Eddy Corridor to trap and redistribute microplastics. Two eddies, an intrathermocline and a cyclonic eddy, were tracked using the Mesoscale Eddy Trajectories Atlas (META) developed by Aviso+ Altimetry and in situ sampled from 50 m to 1200 m depth. In situ oceanographic data and microplastic concentrations were analyzed to assess spatial patterns and explore possible physical mechanism driving them. Results show that small plastic fragments (<100 μm) dominate in both eddies, but significant differences are found in fibers, higher in the cyclone, and large fragments (>100 μm), higher in the intrathermocline. Relative retention of microplastic was found in both eddies with similar values for small fragments but the intrathermocline eddy showed less accumulation of fibers than the cyclone. Microplastic accumulation tended to occur at the eddy borders, particularly in the intrathermocline eddy, likely driven by a combination of submesoscale instabilities and horizontal shear. Additionally, stratification effects and large-scale transport of microplastic via Mediterranean Water may have influenced the vertical distribution. This study highlights the importance of mesoscale and submesoscale processes in microplastic dynamics and underscores the need for improved in situ sampling techniques and numerical models for a more comprehensive understanding of microplastic transport in the ocean.