Authorship：Lead author   Language：English   Publisher：Environmental Science and Technology  

The vertical distribution of small microplastics (SMPs; 10–300 μm in size) and its relation to water masses were investigated through seawater sampling and hydrographic surveys from the sea surface to 1000 m in the North Pacific Ocean. The average ± standard deviation of SMP concentrations in 12 layers at four stations was 6910 ± 2620 particles m^–3. Concentrations were high in isopycnal layers between potential densities of 23 and 25σ<inf>θ</inf>(100–300 m depths). Elevated concentrations were also frequently detected below the North Pacific Intermediate Water (NPIW), characterized by a salinity minimum around the 26.6–27.0σ<inf>θ</inf>(approximately 600 m depth) isopycnal layers. A simple modeling approach to reproduce the observed SMP distribution suggested two pathways for SMPs floating in surface convergence zones. One pathway is the weak settling of SMPs of which the density becomes close to neutral, causing the along-isopycnal subduction from isopycnal layers outcropping at the sea surface to subsurface layers above the NPIW. Therefore, the global inventory of weakly settling near-neutral SMPs is expected to be high in the subsurface layers. Meanwhile, the strong settling via biological processes causes the other pathway from the surface euphotic layer to deep layers that never outcrop at the sea surface.

DOI： 10.1021/acs.est.5c08983

Web of Science

Scopus

PubMed

Authorship：Lead author   Language：English   Publisher：Science of the Total Environment  

Polystyrene foam is widely used due to its lightweight, impact resistance, and excellent thermal insulation properties. Meanwhile, weak adhesion between beads in polystyrene foam leads to fragmentation, generating a substantial amount of microplastics (<5 mm). Such polystyrene foam debris littered on beaches diminishes the aesthetic value of coastal areas, negatively impacting tourism. Due to its density lower than other plastics, polystyrene foam macroplastics float on the sea surface and, thus, they are significantly influenced by wind drag during oceanic transport. In contrast, polystyrene foam microplastics drifting beneath the sea surface are carried mostly by ocean currents. These properties of polystyrene foam macroplastics and microplastics hinder the elucidation of their transport, distribution, and fate in nature, despite their potential to adversely impact marine ecosystems. To elucidate the generation, transport, and fragmentation processes of polystyrene foam ocean plastics, we conducted concurrent visual observations and surface net towing from seven training vessels around Japan during 2014–2020. Overall, the abundances of polystyrene foam ocean plastics were higher in the Sea of Japan than in the North Pacific south of Japan. The average abundances of polystyrene foam microplastics and macroplastics were 0.33 pieces/m³ and 0.45 pieces/km, respectively, over the entire sea area around Japan. In the Sea of Japan, the peak abundances of polystyrene foam macroplastics occurred in upstream of the Tsushima Current, while the peak for microplastics occurred downstream, suggesting that continuous fragmentation occurred during transport between the two peaks. Backward-in-time particle tracking model experiments suggested that the sources of polystyrene foam macroplastics observed in the Sea of Japan included aquaculture buoys and styrene debris beached around the Tsushima Strait. The present study demonstrated that reducing the release of polystyrene foam aquaculture floats will likely diminish the abundance of ocean plastics in the Sea of Japan.

DOI： 10.1016/j.scitotenv.2024.171421

Web of Science

Scopus

PubMed

Language：Japanese   Publisher：The Japanese Society of Fisheries Science  

DOI： 10.2331/suisan.wa3079

Web of Science

Scopus

CiNii Research

Language：Japanese   Publisher：The Plankton Society of Japan  

「練習船による漂流・海底ごみ調査からみた日本周辺海域の海洋プラスチックごみの現状について」の講演要旨

DOI： 10.24763/bpsj.69.2_105_2

CiNii Research