Particles in Waves: Transport of Microplastics in the Ocean from a Particle Perspective

Michelle DiBenedetto
Postdoctoral Research Fellow


Friday, Feb. 28, 2020, 3:10pm
Chase 105

Plastic pollution in the oceans is a global reality. Small dispersed plastic pieces impact ecosystems, fisheries, and water resources throughout the world. Most of this debris breaks down and persists as small particles, or microplastics. Accurately estimating microplastics accumulation rates and assessing ecosystem risk requires understanding the transport and fate of microplastics in the ocean. Of particular interest is how the characteristics of microplastic particles, such as their shape and size, affect their transport. Particle shape couples to transport through particle orientation, as the orientation of a non-spherical particle controls the lift and drag that it feels while moving through a fluid. A theoretical study shows that spheroidal particles tend to a preferred orientation with a superimposed oscillation under waves. This behavior is a consequence of how the particle samples the flow and can be thought of as the angular analog of Stokes drift. The mean preferred orientation is found to be solely a function of the particle’s shape; it is independent of the wave parameters. The implications of this theoretical result were explored with both numerical and laboratory experiments. The effects of the waves and the particle characteristics are shown to be non-trivial for predicting dispersal of the particles. Results from this work show that accurately predicting the transport, settling velocity, vertical distribution and horizontal dispersion of anisotropic particles in wavy environments requires consideration of the shape and preferred orientation of the particles.


Michelle DiBenedetto is currently a postdoctoral scholar at Woods Hole Oceanographic Institution in the physical Oceanography and Biology Departments. She completed her doctoral work in environmental fluid mechanics at Stanford University in June 2019, where she was awarded the Stanford Graduate Fellowship and Gerald J. Lieberman Fellowship to support her research. She uses experimental, numerical, and theoretical techniques to study how the properties of microplastic particles affect their transport in typical environmental flows, such as ocean surface gravity waves. At Woods Hole, she is studying how zooplankton behave in turbulence. Michelle previously received an M.S. in Civil & Environmental Engineering from Stanford University and a B.S. in Environmental Engineering from Cornell University.