The findings, published in the journal Environmental Science and Technology, show that these powerful flows could be capable of traveling at speeds of up to eight meters per second, carrying plastic waste from the continental shelf to depths of more than 3,200 meters.
Over 10 million tonnes of plastic waste enter the oceans each year. While striking images of floating debris have driven efforts to curb pollution, this visible waste accounts for less than 1% of the total. The missing 99%—primarily made up of fibers from textiles and clothing—is instead sinking into the deep ocean.
Scientists have long suspected that turbidity currents play a major role in distributing microplastics across the seafloor—the University of Manchester was among the first to demonstrate this through their research on ‘Microplastic Hotspots’ in the Tyrrhenian Sea, published in the journal Science. However, until now, the actual process has not been observed or recorded in a real-world setting.
The latest study conducted by the University of Manchester, the National Oceanography Centre (UK), the University of Leeds (UK), and the Royal Netherlands Institute for Sea Research provides the first field evidence showing the process.
The findings pose a significant threat to marine ecosystems and highlight the urgent need for stronger pollution controls.
Dr. Peng Chen, lead author of the study at the University of Manchester, said, “Microplastics on their own can be toxic to deep-sea life, but they also act as ‘carriers’ transferring other harmful pollutants such as PFAS ‘forever chemicals’ and heavy metals, which makes them an environmental ‘multistressor’ which can affect the entire food chain.”
The research focused on Whittard Canyon in the Celtic Sea, a land-detached canyon over 300 km from the shore. By combining in-situ monitoring and direct seabed sampling, the team witnessed a turbidity current in action, moving a huge plume of sediment at over 2.5 meters per second at over 1.5 km water depth. The samples directly from the flow revealed that these powerful currents were not only carrying sand and mud but also a significant quantity of microplastic fragments and microfibers.
Further analysis found that the microplastics on the seafloor are mainly comprised of fibers from textiles and clothing, which are not effectively filtered out in domestic wastewater treatment plants and easily enter rivers and oceans.
Dr. Ian Kane, Geologist and Environmental Scientist at the University of Manchester, who designed and led the research, said: “These turbidity currents carry the nutrients and oxygen that are vital to sustaining deep-sea life, so it is shocking that the same currents are also carrying these tiny plastic particles.”
“These biodiversity hotspots are now co-located with microplastic hotspots, which could pose serious risks to deep-sea organisms.
“We hope this new understanding will support mitigation strategies going forward.”
“The role of canyons acting as an important pathway for the transport of matter, including plastics from shelves to the deep sea, has been emphasized in this study,” said Dr. Furu Mienis of the Royal Netherlands Institute for Sea Research. “During several expeditions within the NOW-funded BYPASS? Project we were able to sample sediment along the Whittard Canyon axis to depths over 3,000 m water depth. At all sites plastics were observed in the sediments. With thousands of canyons incising the continental margins globally, many more of these deep-sea plastic hotspots deposition areas are to be expected.”
Dr. Mike Clare of the National Oceanography Centre, who was a co-lead on the research, added: “Our study has shown how detailed studies of seafloor currents can help us to connect microplastic transport pathways in the deep-sea and find the ‘missing’ microplastics. The results highlight the need for policy interventions to limit the future flow of plastics into natural environments and minimize impacts on ocean ecosystems.”
The study team is now focusing on efforts to better understand the effect that microplastics have on marine organisms, such as sea turtles and deep-sea fauna.
