4:00 PM - 4:15 PM
[MIS20-09] Distribution of Microplastics in the Deep-sea Sediments
Keywords:Microplastic, Deep-sea floor, Trench
Marine plastic pollution is of global concern, and one of the Sustainable Development Goals (SDGs) set by the United Nations includes the reduction of marine pollution, including plastic, as one of its targets. Plastics are miniaturized by ultraviolet light and waves, and especially those particles smaller than 5 mm are called microplastics (MPs), and there are concerns about their adverse effects on marine organisms. It is an urgent issue to understand the actual status of MP pollution in the ocean, and it is essential to identify the sources and routes of plastic spills in order to properly regulate plastics and take measures against marine outflow.
MPs exist not only in the sea surface and water column, but also in sediments Especially, they are accumulated at the bottom of ocean trenches. In this study, we focused on the possibility of MPs transport from Sagami Bay, which has the largest population density in Japan in its hinterland, to the plate triple junction. We compared the number of MPs in the sediments of Sagami Bay and the triple junction to examine the transport process of MPs from the bathyal to the hadal zone.
Sediment samples at two stations of Sagami Bay (St. 1: off Hatsushima, 855 m water depth; St. 2: center of the bay, 1,387 m water depth) and at two stations of triple junction (St. 4, 9,218 m water depth; St. 5, 9,232 m water depth) were collected with push corers manipulated by the HOV Shinkai 6500 and a free-fall camera system, respectively, during the research cruise of R/V Yokosuka YK19-11. Sediment samples were subjected to specific gravity separation using sodium iodide (NaI), dissolution of calcium carbonate using hydrochloric acid, and dissolution of organic matter using Fenton treatment to separate MPs from the sediment. The separated MPs were stained with Nile Red and observed and counted under a fluorescence microscope.
The results shows that the number of MPs per dry weight of sediment at the sediment surface (0-1 cm) was 25.5±19.3 MPs/g at St. 1, 67.5±14.7 MPs/g at St. 2, 26.6±0.05 MPs/g at St. 4, and 48.8 MPs/g at St. 5, respectively. The highest number of MPs was detected in the center of Sagami Bay, while the same level of MPs as those in Sagami Bay was detected at the two stations at the plate triple junction, which are far from human activities. In addition, no particles larger than 250 µm in diameter were detected at the two stations of the plate triple junction, and the average diameter tended to be smaller than that of the two stations in Sagami Bay. These results suggest that the MPs at the plate triple junction are transported through the submarine canyons, and that size fractionation of MPs occurs during the transport process. In the future, we plan to analyze the accumulation and depositional processes of MPs in more detail by using micro-Fourier Transform Infrared Spectroscopy (µ-FT-IR) to identify the types of plastics and by dating of the sediments.
MPs exist not only in the sea surface and water column, but also in sediments Especially, they are accumulated at the bottom of ocean trenches. In this study, we focused on the possibility of MPs transport from Sagami Bay, which has the largest population density in Japan in its hinterland, to the plate triple junction. We compared the number of MPs in the sediments of Sagami Bay and the triple junction to examine the transport process of MPs from the bathyal to the hadal zone.
Sediment samples at two stations of Sagami Bay (St. 1: off Hatsushima, 855 m water depth; St. 2: center of the bay, 1,387 m water depth) and at two stations of triple junction (St. 4, 9,218 m water depth; St. 5, 9,232 m water depth) were collected with push corers manipulated by the HOV Shinkai 6500 and a free-fall camera system, respectively, during the research cruise of R/V Yokosuka YK19-11. Sediment samples were subjected to specific gravity separation using sodium iodide (NaI), dissolution of calcium carbonate using hydrochloric acid, and dissolution of organic matter using Fenton treatment to separate MPs from the sediment. The separated MPs were stained with Nile Red and observed and counted under a fluorescence microscope.
The results shows that the number of MPs per dry weight of sediment at the sediment surface (0-1 cm) was 25.5±19.3 MPs/g at St. 1, 67.5±14.7 MPs/g at St. 2, 26.6±0.05 MPs/g at St. 4, and 48.8 MPs/g at St. 5, respectively. The highest number of MPs was detected in the center of Sagami Bay, while the same level of MPs as those in Sagami Bay was detected at the two stations at the plate triple junction, which are far from human activities. In addition, no particles larger than 250 µm in diameter were detected at the two stations of the plate triple junction, and the average diameter tended to be smaller than that of the two stations in Sagami Bay. These results suggest that the MPs at the plate triple junction are transported through the submarine canyons, and that size fractionation of MPs occurs during the transport process. In the future, we plan to analyze the accumulation and depositional processes of MPs in more detail by using micro-Fourier Transform Infrared Spectroscopy (µ-FT-IR) to identify the types of plastics and by dating of the sediments.