Over 10 million tons of plastic waste enters the sea every year. A terrifying fact, right? But there is on the other: in reality, we only see 1% of this plastic; the portion that floats on the surface of the ocean. What happens to the remaining 99% is still unclear.
Plastic debris is gradually divided into smaller and smaller fragments in the ocean, to form particles smaller than 5 millimetres, the so-called “microplastics”. Recently, experts have found up to 1.9 million pieces of microplastic in a 5 cm thick layer covering only one square meter, the highest levels ever recorded on the ocean floor.
The plastics that once floated can sink as they are covered with algae or if tied with other sticky minerals and organic matter. Recent research has shown that rivers also carry microplastics into the ocean and laboratory experiments have revealed that avalanches of giant submarine sediments can carry these tiny particles along canyons at greater depths.
Specifically, the experts have conducted experiments at our Tyrrhenian Sea and studied the bottom currents that flow near the bottom of the sea. These currents are driven by differences in salinity and water temperature as part of an oceanic circulation system that crosses the globe. They extracted samples from the bottom of the sea and then examined them in the laboratory: most of the microplastics found on the bottom of the sea are fibres of clothes and fabrics.
These deep ocean currents also carry hydrogen peroxide and nutrients, which means that the hotspots of the seabed where microplastics accumulate can also harbour important ecosystems.