A microplastic particle drifts on the surface of a warm sea. Within days, invisible hitchhikers, bacteria and single-celled algae, cover it.
This living film acts as ballast: the particle becomes heavier and starts to sink. In a new global model, oceanographers have for the first time tracked the fate of such "hitchhiking" plastic across the entire planet. To the usual coordinates (latitude, longitude, and depth) they added one more: the biomass density on the particle's surface. Thus, each piece of plastic now has its own story of sinking and resurfacing.
Once caught in a subsurface jet, a particle can travel far from the center of a garbage patch. Later, bacteria die off, the film thins, and the plastic resurfaces, but in a different place. This makes subtropical garbage patches more diffuse, and their peak concentrations drop.
Comparison with trawl survey data showed that the model with biofouling makes fewer errors. The share of large discrepancies with observations nearly halved — from 25% to 13%.
Ocean plastic is not just trash; it's a transportation system with a living engine. Microbes silently redistribute it throughout the water column, and now this mechanism can be seen in numbers.
The bacterial film on a microplastic particle weighs several times less than the particle itself, but that's enough to send it on a multi-day journey into the depths.
In Stanislaw Lem's novel "Solaris," the ocean itself controlled the movement of particles — Earth's ocean does something similar with the help of microbes.