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Scientists have identified the highest levels of microplastics ever recorded on the seafloor.
The contamination was found in sediments extracted from the bottom of the Mediterranean, near Italy.
The analysis, led by the University of Manchester, found up to 1.9 million pieces of plastic per square meter.
These items likely included clothing fibers and other synthetic textiles, and small fragments of larger objects that had broken down over time.
The researchers’ investigations lead them to believe that microplastics (less than 1mm) are being concentrated at specific locations on the ocean floor by powerful bottom currents.
“These currents build what are called drift deposits; think of the underwater sand dunes,” explained Dr. Ian Kane, who led the international team.
“They can be tens of kilometers long and hundreds of meters high. They are among the largest accumulations of sediment on Earth. They are predominantly made of very fine silt, so it is intuitive to expect microplastics to be found within them.” he told BBC News.
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Source: I. Kane / Manchester Uni
Something of the order of four to 12 million tons of plastic waste was estimated to enter the oceans each year, primarily through rivers.
Media headlines have focused on the large aggregations of debris that float in turns or wash away with tides on shorelines.
But this visible litter is believed to represent only 1% of the marine plastic budget. The exact whereabouts of the other 99% are unknown.
Certainly some of them have been consumed by sea creatures, but perhaps the much larger proportion has fragmented and simply sunk.
Many of the fibers will come from clothing and other textiles.
Dr. Kane’s team has already shown that deep sea trenches and ocean canyons can have high concentrations of microplastics in their sediments.
In fact, the group’s water tank simulations have shown how efficiently mud, sand and silt flows of the type that occurs in canyons will drag and move fibers to even greater depths.
“A single one of these underwater avalanches (‘turbidity currents’) can transport huge volumes of sediment for hundreds of kilometers across the ocean floor,” said Dr. Florian Pohl of Durham University.
“We are only beginning to understand from recent laboratory experiments how these flows transport and bury microplastics.”
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There is nothing unusual in the study area in the Tyrrhenian basin between Italy, Corsica and Sardinia.
Many other parts of the world have strong deep-water currents driven by contrasts in temperature and salinity. The issue of concern will be that these currents also supply oxygen and nutrients to deep-sea creatures. And so, following the same route, microplastics could be installed at critical points of biodiversity, increasing the possibility of ingestion by marine life.
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Beach plastic can be a very small fraction of the waste there is
Professor Elda Miramontes from the University of Bremen, Germany, is co-author of the article in the journal Science that describes the discovery of the Mediterranean.
She says that the same effort shown in the battle against the coronavirus must now take on the scourge of ocean plastic pollution.
“We are all making an effort to improve our safety and we all stay home and change our lives, changing our working life or even stopping working,” he told BBC News. “We are doing all of this so that people are not affected by this disease. We have to think the same way when we protect our oceans.”
Roland Geyer is a professor of industrial ecology at the Bren School of Environmental Science and Management, University of California, Santa Barbara.
He has been at the forefront of researching and describing the waste streams through which plastic reaches the oceans.
He commented: “We still have a very poor understanding of how much total plastic has accumulated in the oceans. There seems to be an emerging scientific consensus, which is that most of that plastic is not floating on the surface of the ocean.
“Many scientists now think that most of the plastic is likely to be at the bottom of the ocean, but that the water column and beaches also contain large amounts.”
“We really should all be fully focused on preventing plastic from entering the oceans in the first place.”
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I.Kane / Manchester Uni
The sediments were raised as part of the work in a pipeline on the sea floor.
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