27 Jul 2023
 | 27 Jul 2023

Aggregation of Slightly Buoyant Microplastics in Three-Dimensional Vortex Flows

Irina I. Rypina, Lawrence J. Pratt, and Michael Dotzel

Abstract. Although the movement and aggregation of microplastics at the ocean surface has been well studied, less is known about the subsurface. Within the Maxey-Riley framework governing the movement of small spheres with high drag in fluid, aggregation of buoyant particles is encouraged in vorticity-dominated regions. We explore this process in an idealized model of a three-dimensional eddy with an azimuthal and overturning circulation. In the axially symmetric state, particles that do not accumulate at the top boundary are attracted to a closed contour consisting of periodic orbits. Such a contour exists when drag on the particle is sufficiently strong. For small slightly-buoyant particles, this contour is located close to the periodic fluid trajectory. If the symmetric flow is perturbed by a symmetry-breaking disturbance, additional attractors arise near periodic orbits of fluid particles within the resonance zones created by the disturbance. Disturbances with periodic time dependence produce even more attractors, with a shape and location that recurs periodically, and which are composed of quasiperiodic orbits of rigid particles. Not all such contours attract, and particles released in the vicinity may instead be attracted to a nearby attractor. Examples are presented along with mappings of the respective basins of attraction.

Irina I. Rypina et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on egusphere-2023-1624', Francisco Beron-Vera, 04 Aug 2023
  • RC1: 'Comment on egusphere-2023-1624', Francisco Beron-Vera, 08 Aug 2023
  • RC2: 'Comment on egusphere-2023-1624', Anonymous Referee #2, 28 Aug 2023
  • AC1: 'Comment on egusphere-2023-1624', Irina I. Rypina, 29 Sep 2023
  • AC2: 'Comment on egusphere-2023-1624', Irina I. Rypina, 29 Sep 2023
  • AC3: 'Comment on egusphere-2023-1624', Irina I. Rypina, 29 Sep 2023
  • AC4: 'Comment on egusphere-2023-1624', Irina I. Rypina, 29 Sep 2023

Irina I. Rypina et al.

Irina I. Rypina et al.


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Short summary
This paper investigates aggregation of small, slightly buoyant, rigid body particles in a three-dimensional vortex flow. Our goal was to gain insights into the behaviour of slightly buoyant marine microplastic particles in a flow that qualitatively resembles ocean eddies. Attractors are mapped out for the steady axisymmetric, steady asymmetric, and non-steady asymmetric vortices over a range of flow and particle parameters. Simple theoretical arguments are used to interpret the results.