Unveiling the Mystery of Microplastic Accumulation in the Ocean
The ocean is a vast, mysterious place, and one of its most pressing secrets is the accumulation of microplastics. While we know the location of the great garbage patches, the hidden depths of the ocean still hold many unknowns. But here's where it gets controversial...
A recent study published in the journal Chaos by researchers from the Woods Hole Oceanographic Institution has shed light on a theory of how microplastic particles accumulate in ocean eddies. The study, titled 'A theory for attractors of microplastic particles in the resonant structures of a 3D eddy', offers a fascinating insight into the behavior of these tiny particles in the vast ocean.
The researchers, Larry Pratt and Irina Rypina, began by modeling how fluid moves in a rotating cylinder, a laboratory setup commonly used to investigate large-scale ocean and atmospheric flows. When the cylinder lid is tilted, fluid trajectories change, and particle paths are broken up into a tangled flow of chaotic orbits and new donut-shaped circulations. These circulations can give rise to attractors of slightly buoyant, small particles, stable behaviors that a system settles into.
"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," said Pratt. "So, to a first approximation, the microplastic particles are just following the fluid trajectories." However, the complication is that the microplastics have inertia and disrupt the fluid around them, causing them to slowly stray from the fluid's usual path.
Pratt and Rypina exploited the mathematics behind this to develop a theory for how and where particles accumulate. Applying the theory to ocean flows can help determine subsurface areas with high concentrations of microplastics. They found that particle accumulation occurs in the center of tubelike structures that wind around circular currents. Many such structures may exist, resulting in multiple 'attractors' of small particles. Each attractor resembles a twisted, closed loop that particles move along, spiraling upward and downward in the 3D flow.
The study's conclusions reflect experimentally and numerically observed flows, but the researchers have plans to add more realistic complications. "The main thing we need to consider is the effects of small-scale turbulence. The theory is valid for spherical particles, but most microplastics in the ocean have very irregular shapes," said Pratt. "Another challenge for the future is trying to track those, [and] in the immediate future, we're hoping that the theory will inform sampling strategies and lead to a better understanding of where plastics might be accumulating."
This study is a significant step forward in understanding the behavior of microplastics in the ocean. It offers a new perspective on the accumulation of these tiny particles and provides a basis for further research and development of sampling strategies. But the question remains: what other secrets does the ocean hold, and how can we uncover them?
What do you think about this study? Do you agree with the researchers' findings? Share your thoughts in the comments below!
