Large volumes of microplastics are transported to the deep sea by turbidity currents

Abstract Microplastics pervade the global seafloor, yet the mechanisms by which this pollutant is increasingly transported to the deep sea remain unclear. Fast-moving sediment avalanches (called turbidity currents) are hypothesized to efficiently transport microplastics into the deep sea, yet, while inferred from field sampling of the seafloor, this has never been demonstrated outside of a laboratory setting. Here, we provide the first direct field-scale evidence that turbidity currents in submarine canyons not only transport globally-important volumes of mineral and organic matter into the deep sea, but also carry large quantities of anthropogenic particles, including microfibers and microplastic fragments. In-situ hydrodynamic monitoring in the Whittard Canyon (NE Atlantic Ocean), coupled with sampling of the seafloor and material suspended by turbidity currents reveal that even a canyon whose head lies hundreds of kilometers from land acts as an efficient conduit to flush sediment and pollutants from the continental shelf to >3200 m water depth. Frequent and fast turbidity currents supply oxygen and nutrients that sustain deep-sea biodiversity and fishing grounds in, and adjacent to, such submarine canyons. Our results therefore provide the first real-world evidence to confirm that these biodiversity hotspots are co-located with microplastic hotspots, indicating that the >5000 land-detached canyons that incise all of Earth’s submerged continental margins may be important but previously-unproven conveyors of anthropogenic pollution to the deep sea.