Transport of floating marine litter in the coastal area of the south-eastern Bay of Biscay: A Lagrangian approach using modelling and observations

Marine litter is identified as the major ocean pollution today, with a significant impact on the environment. The transport of litter by ocean circulation is still poorly understood, and the management of marine litter remains a major challenge for local authorities. This work investigates the transport of floating marine litter (FML) in the coastal area of the south-eastern Bay of Biscay. It provides a first assessment of the use of operational ocean observations and models for the support of FML management in this region. The study is based on a Lagrangian modelling approach, using ocean surface velocity forcing by (i) measurements with High-Frequency Radars and (ii) predictions from the IBI Copernicus model. The IBI model is first assessed in a Lagrangian perspective using different observations of surface ocean currents and transport. Then, analyzing a multiyear hindcast of the Lagrangian model, high retention is shown in the southeast during spring and summer. Northward dispersion is obtained along the French coast during autumn and winter. In winter, large river inflows are not compensated by the inner shelf transport, resulting in the highest material densities along the coast. The results also suggest that the Iberian Poleward Current may act as a cross-shore transport barrier in the area.