Microplastic in Astonishing Quantities Found on the Seafloor

More than ten million tons of plastic are dumped into the oceans every year, but we only see about one percent of it, namely the pieces that float on the surface. But what happens to the rest of 99 percent missing garbage patches?

Plastic waste is desegregated into smaller and smaller parts in the ocean, forming microplastics that are tinier than 5 mm. New research demonstrates that powerful currents take these microplastics together with the seafloor into massive ‘drifts,’ which gather them in staggering amounts. The study found up to 1.9 million segments of microplastic is a five cm-thick layer spread across only one square meter – the highest levels of microplastics ever recorded on the seafloor.

Transports of Microplastic

Although microplastics have been discovered on the ocean floor all over the world, researchers were not clear how they got there and how they disperse. They believed that microplastics would separate out based on their size or density, in a similar way to natural sediment.

However, plastics are different: some float, but more than half of them get to the ocean floor. Plastic waste that once floated can sink as they get covered in algae, or if caught in other sticky minerals and organic matter.

Another new research has shown that rivers transport microplastics to the ocean as well, and lab investigations unveiled that massive underwater avalanches of sediment can also transport these small particles together with deep-sea canyons to further depths.

A newly-discovered global network of deep-sea currents apparently transports microplastics, designing plastic hotspots within gigantic sediment drifts.

Creatures on the Ocean Floor are Potentially Harmed

The team of scientists investigating the issue in the recent study have analyzed a region in the Mediterranean, on the western coast of Italy, known as the Tyrrhenian Sea, and examined the deep-sea currents that flow close to the seafloor.

[Image: Ian Kane, Reader in Geology, University of Manchester and Michael Clare, Principal Researcher in Marine Geoscience, National Oceanography Centre.]
These currents are conducted by discrepancies in water salinity and temperature as part of a system of ocean circulation that runs the planet. Researchers assayed sediment samples from the seafloor, taken with box-cores, which are similar to big cookie cutters.

The team then separated microplastics from the sediment and analyzed them under microscopes, utilizing infrared spectroscopy to figure out what types of plastic polymer were there. Most microplastics discovered on the seafloor are fibers from clothes and textiles, and can usually be consumed and absorbed by organisms in the oceans.

Even though individual microplastics are usually non-toxic, numerous research studies show the accumulation of toxins on their surfaces is dangerous to the organisms if ingested.

These deep ocean currents also transport oxygenated water and nutrients, which means that the seafloor hotspots where microplastics end up may also be the place where important ecosystems such as deep-sea coral reefs that have developed to rely on these flows but are now getting massive amounts of toxic microplastics instead.

The cheap plastic items we usually take for granted, usually end up somewhere on the globe ultimately. The clothes we throw may remain for decades or centuries on the seafloor, harming the creatures in their own home.

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