Dispersal of Microplastics in the Marine Environment (DIME)

With 8 million tonnes of plastic entering our oceans each year, marine plastics are one of the biggest threats facing the marine environment. Over 90% of marine plastics are microplastics (<5 mm), resulting from the degradation of larger plastics (diffuse sources), or directly input to the marine environment from point sources (e.g. synthetic textile fibres) and, due to bioaccumulation, are particularly harmful to marine life. Measurements of the transport pathways and accumulation of microplastics in the marine environment are challenging, due to the range of spatial/temporal scales, and the complexity of physical processes in the nearshore "white ribbon". We therefore adopt a multidisciplinary modelling approach to simulate the transport of plastics, from diffuse/point sources, through the marine environment. We will investigate a range of transport pathways, including localized dispersal of microplastics from their source (e.g. wastewater outflows), and subsequent dispersal into intertidal/terrestrial environments (e.g. beaches and dune systems), in addition to their entrainment and dispersal via large scale ocean currents. The project will result in revised source/pathway/sink budget estimates of microplastic fluxes across all scales of the marine environment.
Meso-scale dispersal will be simulated using grid-based (Eulerian) models, interrogating existing global model outputs, and developing project-specific coastal models. The "white ribbon" is particularly challenging, due to the interaction of multiple physical processes; and to include processes such as wave breaking and longshore currents, we will apply meshless (Lagrangian) models to simulate how particles interact with this zone - processes that would be heavily parameterized in Eulerian models. The overarching aim of the project is to quantify microplastic budgets in shelf sea environments, understanding their providence, transport pathways, and fate. Although this will primarily be achieved by the modelling approaches highlighted above, the simulations will be supplemented, and calibrated, using localized in situ sampling of microplastics from sea bed sediments.