The mass of “invisible” microplastics found in the upper waters of the Atlantic Ocean is approximately 12 to 21 million tonnes, according to research published in the journal Nature Communications.

Significantly, this figure is only for three of the most common types of plastic litter in a limited size range. Yet, it is comparable in magnitude to estimates of all plastic waste that has entered the Atlantic Ocean over the past 65 years: 17 million tonnes. This suggests that the supply of plastic to the ocean have been substantially underestimated.

The lead author of the paper, Dr Katsiaryna Pabortsava from the U.K. National Oceanography Centre (NOC), said: “Previously, we couldn’t balance the mass of floating plastic we observed with the mass we thought had entered the ocean since 1950. This is because earlier studies hadn’t been measuring the concentrations of ‘invisible’ microplastic particles beneath the ocean surface. Our research is the first to have done this across the entire Atlantic, from the U.K. to the Falklands.“

Co-author, Professor Richard Lampitt, also from the NOC, added: “If we assume that the concentration of microplastics we measured at around 200 meters deep is representative of that in the water mass to the seafloor below with an average depth of about 3,000 meters, then the Atlantic Ocean might hold about 200 million tonnes of plastic litter in this limited polymer type and size category. This is much more than is thought to have been supplied.“

This study builds on the NOC’s cutting-edge research into marine plastic contamination, which aims to better understand the magnitude and persistence of exposure to plastics and the potential harm it can cause. This work was supported by the EU H2020 AtlantOS program and the NOC.