Oceanward surface transport from the NW African upwelling zone by coastal jet detachment and filaments

Abstract

The oceanward surface transport of particles, including marine litter, from the northwestern African upwelling zone is influenced by multiple interacting physical processes. This study applies the OceanParcels Lagrangian framework to investigate the mechanisms that may contribute to oceanward surface transport in this region, motivated by the hypothesis that the northwestern African upwelling system could represent a potential source of marine litter in the vicinity of the Canary Islands. The simulations suggest that the coastal jet stream and its detachment, upwelling filaments, and Stokes drift play key roles in shaping particle trajectories. In particular, coastal jet detachment appears to organize surface transport into narrow, oceanward-oriented particle corridors, while upwelling filaments may provide additional offshore export pathways. Stokes drift introduces a predominantly southward deflection that can reduce or modulate oceanward advection and enhance alongshore transport. These results provide a process-based, model-derived first assessment of previously understudied oceanward transport corridors in the NW African upwelling system. They are consistent with the hypothesis that this region may contribute to surface tracer transport toward the Canary Islands. However, caution is required when extrapolating these findings to marine debris, as windage is not included and may significantly alter transport pathways. Continued investigation, including observational validation and improved surface forcing representations, will help further constrain the mechanisms shaping particle transport in the NW African upwelling system.