Assessing and optimizing the role of wind forcing and upper-ocean dynamics in marine pollution transport simulations using surface drifters in the Canary Current System

Abstract. This study investigates the sensitivity of undrogued drifter trajectory simulations in the Macaronesia region, selected for their similarity to the behavior of marine litter transport in the upper ocean. The research evaluates the influence of various physical processes, including advection schemes, horizontal dispersion, windage and Stokes drift. A total of 320 simulations were conducted, incorporating different combinations of these processes, the modeled trajectories were compared with real drifter data. The analysis demonstrated that the inclusion of windage and/or Stokes drift significantly improved the agreement between modeled and observed trajectories, particularly when windage factors (WDF) ranged from 2.5 % to 5 %. Horizontal dispersion exhibited minimal influence on the trajectories, indicating that turbulent diffusion had a limited effect under the study conditions. While both advection schemes (RK2 and RK4) produced comparable results, RK4 outperformed RK2 in scenarios involving pronounced mesoscale activity. This research highlights the relevance of using undrogued drifters to mimic marine litter transport and underscores the importance of incorporating windage and/or Stokes drift in trajectory simulations, particularly in regions like Macaronesia, where mesoscale processes play a critical role.