Numerical simulations of non-buoyant plastic dispersion around the Iberian Peninsula

Abstract

The continuous release and accumulation of plastics in the ocean is a major environmental concern as shown by the ongoing negotiations for a Global Plastics Treaty led by the United Nations. Numerical models have proven to be valuable tools to improve our knowledge about how marine plastics disperse, identifying, for example, accumulation areas and the pathways followed by plastics to reach them. While models have been widely used for studying floating plastic, there are fewer studies focused on plastic accumulation on the seafloor. In this study, we used a 3D Eulerian model to predict the accumulation patterns of non-floating plastics around the Iberian Peninsula. We selected four of the most common types of plastics and distinguished two scenarios: one considering only plastics from land-based sources and another from sea-based activities. The integrations simulate the dispersion of plastics over 5 years, starting from a plastic-free sea and modeling the daily introduction of plastics into the sea as would be expected under real conditions. Our experiments show an area virtually free of plastics in the southwestern Gulf of Cadiz, likely due to the magnitude of the deep-sea currents occurring in this region, which prevent plastics from settling down. Non-buoyant plastics originating in the coast tend to accumulate on the continental shelf but can gradually disperse into the open ocean and even reach seamounts, depending on how far these seamounts are from land. The inclusion of sea-sourced plastics results, as expected, in a more widespread distribution of plastics towards the open sea.