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March 30, 2021

A large number of plastic debris were found on the Boso Peninsula seafloor at a depth of approximately 6,000 m
-Going to the deep-sea in search of missing plastic-

1. Key points

Little is known about the extent of plastic debris on the abyssal seafloor.
A massive number of disposable plastics, such as plastic bags and food packaging, were found around 500 km off Boso Peninsula during a seafloor survey at a depth of approximately 6,000 m. This region has been identified as a potential reservoir of plastic debris.

The density of plastic debris found on the abyssal seafloor off the Boso Peninsula (4561 items/km2 in average) was two orders of magnitude higher than previously recorded values for plastic debris on abyssal seafloors. The value was higher than those recorded for depression features, such as trenches and submarine canyons, where debris is suspected to accumulate easily.

2. Overview

A group of researchers led by Ryota Nakajima, a researcher at Research Institute for Global Change (RIGC), Marine Biodiversity and Environmental Assessment Research Center (BioEnv), Marine Plastics Research Group (M-Plastics), Japan Agency for Marine-Earth Science and Technology (JAMSTEC) undertook an assessment of the abyssal plain (*) approximately 500 km off the Boso Peninsula and at a depth of approximately 6,000 m using a human occupied vehicle (Shinkai 6500) in September 2019. They are the first time to find that a large number of plastic debris had accumulated on the seafloor at this region.

Since plastics are not readily decomposed by living organisms, there are concerns about the impact of plastic on the ecosystem. Countries around the world are working to understand the extent of marine litter and to prevent the emission of plastic pollution. Over 10 million metric tons of plastic debris continue to flow into the ocean each year but only 440,000 metric tons are found floating on the surface of the ocean. The majority of the rest disappear from the surface layer and are considered to be missing plastics. The deep seafloor is believed to be a reservoir for these plastic debris but the reality is not well understood.

Therefore, this study investigated the Kuroshio extension/recirculation gyre off the Boso Peninsula, one of the sea areas where a large number of plastic debris is expected to accumulate in adjacent waters off Japan. On the seafloor just below the assessment area (5718-5813m water depth), plastic debris, especially disposable plastics such as plastic bags, were found. The density of the debris in the abyssal zone was the highest recorded of all marine zones with similar water depths. Food packaging that was manufactured in 1984 was found in an almost intact state. This means that the deterioration of plastic is extremely slow in the deep-sea where the water temperature is low.

This finding was published in Marine Pollution Bulletin Magazine on March 30th (Japan time).

Massive occurrence of benthic plastic debris at the abyssal seafloor beneath the Kuroshio Extension, the North West Pacific
Ryota Nakajima1, Masashi Tsuchiya1, Akinori Yabuki1, Shuhei Masuda1, Tomo Kitahashi1, Yuriko Nagano1, Tetsuro Ikuta1, Noriyuki Isobe1, Haruhiko Nakata2, Heather Ritchie1, Kazumasa Oguri3, Satoshi Osafune1, Kiichiro Kawamura4, Maki Suzukawa4, Takuya Yamauchi2, Koichi Iijima1, Takao Yoshida1, Sanae Chiba1, Katsunori Fujikura1
1.Japan Agency for Marine-Earth Science and Technology (JAMSTEC)
2.Faculty of Advanced Science and Technology, Kumamoto University
3.Department of Biology, Nordcee and Danish Center for Hadal Research, University of Southern Denmark
4.Graduate School of Science and Technology for Innovation, Yamaguchi University

[Supplemental information]

Abyssal plain: A deep sea bottom with gentle slopes. The seafloor has various topographical features, similar to mountains and valleys on land, but the topography of the abyssal plain seafloor (especially 4000m-6000m) is mostly flat.


(For this study)
Ryota Nakajima, Researcher, Research Institute for Global Change(RIGC), Marine Biodiversity and Environmental Assessment Research Center(BioEnv), Marine Plastics Research Group (M-Plastics), JAMSTEC
(For press release)
Public Relations Section, Marine Science and Technology Strategy Department, JAMSTEC
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