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Scientists discover missing plastics

Plastic pollution

A new study provides the first direct link between the behaviour of ocean currents and the concentrations of seafloor microplastics.

6 May 2020

Muriel Cozier

An international researcher team say that they have found the ‘highest levels of micro plastics ever recorded on the sea floor, with  up to 1.9 million pieces in a thin layer covering just one square meter.’

Publishing their findings in the journal Science, researchers from the UK, Germany and France have shown how deep currents act as ‘conveyor belts’, transporting tiny plastic fragments and fibres across the sea floor.  The researchers say that these currents can concentrate microplastics within huge sediment accumulations, which they have termed ‘microplastic hotspots’. These hotspots appear to be deep-sea equivalents so the so-called ‘garbage-patches’ formed by currents on the ocean surface.

‘Almost everybody has heard of the infamous ocean ‘garbage patches’ of floating plastic, but we were shocked at the high concentrations of microplastics we found on the deep-seafloor,’ said lead author of the study Dr Ian Kane from The University of Manchester.

The team collected sediment samples from the seafloor of the Tyrrhenian Sea, part of the Mediterranean Sea, and combined these with calibrated models of deep ocean currents and detailed mapping of the seafloor. In the laboratory the microplastics were separated from sediment, counted under the microscope and further analysed using infra-red spectroscopy to determine the plastic types. This information allowed the team to determine how ocean currents control the distributions of micro-plastics on the seafloor.

‘We discovered that microplastics are not uniformly distributed across the study area; instead they are distributed by powerful seafloor currents which concentrate them in certain areas,’ Dr Kane said.

Researchers assert that the floating plastic, which has caught the attention of the public, accounts for less than 1% of the plastic that enters the world’s oceans. The missing 99% is thought to occur in the deep ocean, but until now it has been unclear where it actually ended up. Microplastics on the seafloor are mainly comprised of fibres from textile clothing. These are not effectively filtered out in domestic waste water treatment plants and easily enter rivers and oceans.

Science DOI:10.1126/science.aba5899

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