We can't find the internet
Attempting to reconnect
Something went wrong!
Hang in there while we get back on track
Clustering of buoyant tracer in quasi-geostrophic coherent structures
Summary
Using Lagrangian particle tracking in a turbulent quasi-geostrophic ocean model, researchers found that buoyant floating tracers cluster inside coherent vortex structures due to ageostrophic circulation effects, with implications for understanding how surface plastic debris concentrates in ocean eddies.
We have investigated the dynamics of floating tracer in an idealised turbulent quasi-geostrophic ocean by advecting Lagrangian particles in a high-resolution velocity field enhanced by the potential flow associated with vortex stretching. At first order in the Rossby number expansion, this component of the ageostrophic circulation can be derived through a diagnostic equation in terms of the geostrophic velocities. Borrowing methods from the theory of Lagrangian coherent structures, we identify coherent material loops around strong vortex cores using the Lagrangian averaged vorticity deviation (LAVD). Building on studies of clustering in kinematic, stochastic velocity fields, we utilise methods from statistical topography to show that the coherent vortices dominate the distribution of extreme values of the concentration field. We find that the presence of clusters and voids in a coherent vortex depends on more than just the sense of rotation, but also on the full evolution of the vorticity over its lifecycle. We identify the mechanism behind the cluster formation that respects the symmetries of the quasi-geostrophic equations but can be expected to hold robustly in more complicated regimes, due to the simple physical description. The association of cluster formation with vortex stretching implies that LAVD is a particularly relevant metric for floating tracer dynamics. The detection of intense clustering also has implications for reaction rates between ocean-borne flotsam, meaning that our results are relevant to understanding the general risk of floating microplastics and marine biological populations.
Sign in to start a discussion.
More Papers Like This
On Clustering of Floating Tracers in Random Velocity Fields
This mathematical modeling study explores how floating particles — including microplastics — cluster into dense patches on the ocean surface under turbulent currents, finding that realistic time-correlated ocean flows produce clusters far faster than simpler models predict. Understanding this clustering behavior is important for accurately assessing where microplastic pollution concentrates in the ocean and how organisms encounter it at ecologically meaningful densities.
Particle dispersion and clustering in surface ocean turbulence with ageostrophic dynamics
This paper is not directly about microplastics; it uses numerical ocean simulations to model how small-scale turbulence and ageostrophic dynamics affect the clustering and dispersion of floating particles at the ocean surface, with relevance to understanding how marine debris concentrates in convergence zones.
Large eddy simulations of the accumulation of buoyant material in oceanic wind-driven and convective turbulence
Researchers used large eddy simulations to show that buoyant materials like microplastics accumulate at specific ocean surface zones driven by convergent currents under both wind-driven and convective turbulence, improving understanding of how plastics concentrate at the sea surface.
Aggregation of Slightly Buoyant Microplastics in Three-Dimensional Vortex Flows
This modeling study found that slightly buoyant microplastics preferentially accumulate in vorticity-dominated regions below the ocean surface in three-dimensional eddy flows. This explains why microplastics are found throughout the water column rather than just at the surface, and has implications for their ingestion by organisms at various depths.
Ordering of trajectories reveals hierarchical finite-time coherent sets in Lagrangian particle data: detecting Agulhas rings in the South Atlantic Ocean
Scientists developed a new algorithm for detecting coherent ocean eddies — swirling water masses that can trap and transport floating particles — in large datasets of particle trajectories. Understanding how ocean circulation features move microplastics is important for predicting where marine plastic pollution accumulates.