High resolution modeling of the Indian Ocean circulation designed for Lagrangian dispersion applied to marine plastic pollution

Our project is part of an international and multidisciplinary IRD collaboration aiming to better understand the distribution of plastic litter in the Indian Ocean. This basin, rich in biodiversity, is subject to strong anthropogenic pressure with more than 2.2 billion inhabitants connected to the Ocean via river basins and intense maritime traffic (Honorato-Zimmer et al., 2022). The ocean dynamics is complex, with strong regional and seasonal variability and intense eddy activity as in the Mozambique Channel. To address these issues, we have developed a configuration of the hydrodynamic model SYMPHONIE (Marsaleix et al., 2008) over the Indian Ocean to study the land-sea transfers and sub-basins connectivity. We created a curvilinear grid with two high resolution poles, of the order of 1km, centered on the Mozambique Channel and the Indian coast, from the Arabian Sea to the Bay of Bengal. We show that this high resolution allows us to represent the mesoscale and partly sub-mesoscale structures that play a fundamental role in the transfer and retention of particles at sea. Our simulation is forced by daily riverine freshwater discharges whose plumes influence coastal and seasonal dynamics but also plastic river inputs (Weiss et al., 2021). Thus, we address the challenges of locating and quantifying anthropogenic sources in modeled plastic deployment scenarios as well as simulating their dispersion affected by sinking or rising velocities in ocean currents. Finally, we propose to assess the potential impact by characterizing the major beaching areas co-located with mangrove, coral and sandy coastlines distributed around the basin.
The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)