Ocean eddies — rotating masses of water tens to hundreds of kilometers across that spin off from major currents — are known to transport heat, salt, and nutrients. They are also, it turns out, collecting microplastics.
Researchers at the University of Las Palmas de Gran Canaria sampled two eddies south of the Canary Islands: one cyclonic (rotating counterclockwise in the Northern Hemisphere) and one intrathermocline (embedded within the thermocline, the boundary between warm surface water and cold deep water). In both, microplastic concentrations in the upper two hundred meters were higher than regional background levels. The eddies were accumulating pollution.
The composition differed by eddy type. Small fragments dominated both structures, but fibers were significantly more prevalent in the cyclonic eddy, while larger fragments accumulated in the intrathermocline one. The particle type retained depends on the eddy's internal dynamics — its rotation speed, its depth structure, its degree of isolation from surrounding water.
The finding that complicates cleanup efforts is that an eddy's history matters. Where it formed, what other eddies it interacted with, how long it's been spinning — all of these influence its microplastic cargo. Two eddies of the same type, the same size, in the same ocean can carry different concentrations of different particles because they had different biographies.
Eddies are dynamic reservoirs. They don't just passively carry what they encounter — they selectively retain certain particle types based on their internal physics. The ocean's microplastic distribution isn't a simple function of where plastics enter the water. It's a function of where eddies form, how they move, and what they hold. The transport infrastructure of the ocean is sorting the pollution.