Numerical simulation of oil spill dispersion and weathering in the Alboran Sea: A case study of its North-Eastern Coast

Abstract

Accidental oil spills in the Alboran Sea represent a high-risk hazard because intense maritime traffic, semi-enclosed circulation, and sensitive Moroccan coastal ecosystems converge within a narrow coastal corridor. Operational-scale simulations for the Nador-Saïdia sector remain scarce, particularly for persistent heavy fuel oil and for the combined effects of mesoscale circulation, wind drift, Stokes drift, vertical mixing, and weathering. This study applies the OpenOil module of the OpenDrift Lagrangian framework to simulate a hypothetical release of 100 tons of heavy fuel oil (Generic Bunker C) offshore the Driouch coast (35.45° N, 2.95° W) over a seven-day (168 h) period, beginning on 02 July 2024 at 12:00 UTC. The model was forced with CMEMS Mediterranean physics fields, CMEMS Mediterranean wave data, and NOAA-GFS 10 m winds. The selected summer scenario represents a high-impact vulnerability case characterized by strong stratification, sea-breeze influence, peak beach-tourism exposure, and high ecological sensitivity of the Marchica Lagoon, Moulouya River estuary, and Cap des Trois Fourches. The simulations incorporated high-resolution meteorological and oceanographic forcing from CMEMS and NOAA-GFS. Results highlight the strong influence of mesoscale circulation patterns in the Alboran Sea, particularly the interaction between regional gyres, the Algerian Current, and local wind-driven drift. Lagrangian trajectories indicate a dominant east–southeastward transport, posing a direct threat to environmentally sensitive coastal areas. By the end of the simulation, 4,253 particles were stranded, corresponding to approximately 85.1 t of oil, while 747 particles remained active at sea, corresponding to approximately 14.9 t. Weathering was dominated by emulsification and viscosity increase, whereas evaporation remained limited to approximately 10–15% of the released mass and natural dispersion remained below 10%. The revised analysis indicates that high viscosity and density lower than seawater explain the long surface residence time of fresh Bunker C, while sedimentation risk becomes critical mainly in shallow, sediment-rich environments through oil-mineral aggregation. The study identifies priority coastal exposure pathways and provides management-relevant guidance for preparedness planning, including pre-positioning of response equipment adapted to viscous oils, rapid protection of lagoon inlets where feasible, and transboundary coordination between Morocco and Algeria.