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).
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