Researchers at Woods Hole developed a 3D fluid model showing that spherical microplastics can converge into stable, twisted closed-loop 'eddies' beneath the ocean surface. Using a rotating-cylinder laboratory analogue and mathematical analysis, they found attractors that spiral up and down, concentrating particles below the surface. The model may guide more effective subsurface sampling and cleanup, but it assumes spherical particles and omits small-scale turbulence, so real-world behavior may differ.
Underwater Tornadoes: Microplastics Form Twisted, Closed-Loop Eddies Beneath the Ocean Surface
Plastic Tornadoes Are Churning in Our OceansRosemary Calvert - Getty Images
More than a century after the invention of synthetic plastics, microscopic fragments of those materials—microplastics—have become a global environmental and public-health concern. NASA estimates that over eight million tons of microplastics enter the world’s oceans each year, and these particles have been detected from coastal storm systems to human tissues. Yet locating where microplastics accumulate below the surface remains a major scientific challenge.
New 3D Model Reveals Hidden Structures
Researchers Larry Pratt and Irina Rypina at the Woods Hole Oceanographic Institution addressed this problem with a three-dimensional fluid model that simulates how spherical microplastic beads behave in chaotic, ocean-like currents. Their study, published in the journal Chaos, combines mathematical analysis with a laboratory analogue to reveal surprising, organized patterns in what might otherwise seem like random motion.
Rotating-Cylinder Analogue
To mimic large-scale circulation on a manageable scale, the team used a rotating cylinder in which the sidewall and lid spin at different speeds. That configuration reproduces circulation patterns analogous to currents that span hundreds of kilometers, allowing researchers to test how small particles move within complex flows.
Pratt explained: 'If you just threw a small particle into the water with some arbitrary velocity, viscous drag would rapidly bring its motion close to that of the fluid.' This is why particle trajectories often follow the fluid closely—but finite particle inertia can still produce important differences.
Key Findings: Twisted Closed-Loop Attractors
The mathematical analysis predicts that spherical microplastic particles do not remain uniformly dispersed. Instead, they can converge into multiple stable attractors—closed-loop flow structures that twist and spiral upward and downward beneath the surface. The authors liken these features to an "idealized eddy" or a closed-loop tornado that concentrates particles away from the surface and into persistent subsurface bands.
Limitations and Caveats
The theory relies on simplifications: it assumes spherical particles and does not fully account for small-scale turbulence or irregular particle shapes, both of which are common in real ocean conditions. The authors emphasize that changes in particle properties and flow parameters can alter where and whether these attractors form.
Implications for Sampling and Cleanup
Despite its simplifications, the model offers a useful framework for targeting subsurface sampling efforts. If targeted surveys validate these predicted accumulation zones, conservationists and cleanup planners could prioritize areas where microplastics concentrate below the surface—potentially improving the effectiveness of removal and mitigation strategies.
Bottom line: The study provides a new theoretical lens for understanding how microplastics move in three-dimensional ocean flows. While more work is needed to test the model against field data and account for realistic particle shapes and turbulence, the findings point to previously hidden patterns that could help focus future research and remediation efforts.
