The dynamics of biofouled particles in vortical flows

When using mathematical models to predict the pathways of biofouled microplastic in the ocean, it is necessary to parametrise the impact of turbulence on their motions. In this paper, statistics on particle motion have been computed from simulations of small, spherical particles with time-dependent mass in cellular flow fields. The cellular flows are a prototype for Langmuir circulation and flows dominated by vortical motion. Upwelling regions lead to particle suspension and particles fall out at different times. The uncertainty of fallout time and a particle's vertical position is quantified across a range of parameters. A slight increase in settling velocities, for short times, is observed for particles with inertia due to clustering in fast downwelling regions for steady, background flow. For particles in time-dependent, chaotic flows, uncertainty is significantly reduced and we observe no significant increase in the average settling rates due to inertial effects. •Ocean vortices delay he sinking of biofouled microplastic particles•Delayed particle sinking creates uncertainty in a particle’s trajectory•The smallest particles in Langmuir-scale vortices exhibit the largest trajectory uncertainty•The particle’s inertia can largely be neglected in this problem•Unsteady vortical flows reduce the uncertainty of the particle’s trajectory