Diffusiophoretic dispersion of microplastics in oceanic surface flows

Microplastic spreading in the oceans poses a significant global biogeochemical threat. Understanding its transport pathways is therefore of essence in our efforts to predict and mitigate this problem. Before these particles can reach the deep oceanic layers through sedimentation and vertical mixing, surface currents can transport them over vast distances. Through table-top experiments and numerical simulations, designed to mimic the nearly two-dimensional conditions of large-scale oceanic flows, we demonstrate that even slight salinity gradients, which are prevalent in the oceans, can profoundly influence the dispersion of particles in both ordered and chaotic flows. These solute gradients lead to diffusiophoretic migration of particles across the flow streamlines, resulting in either enhanced dispersion or trapping. Our findings suggest that the interaction between flow and salinity gradients can play a crucial role in modulating the dispersion of contaminants and microplastics in marine environments.