5:15 PM - 7:15 PM
[MIS02-P06] Vertical Distribution of Small Microplastics in the Southern Coast of Japan: Comparison with Water Mass Structure
Keywords:Small microplastics, Vertical distribution, Intermediate Oyashio Water
Small microplastics (S-MPs) smaller than 300 µm are challenging to accurately quantify in the ocean due to the lack of established sampling and analytical methods. Recent studies have reported that MP concentrations are higher in the water column than in surface waters (Choy et al., 2019; Kanhai et al., 2018), yet the underlying mechanisms remain unclear. In this study, we collected and analyzed S-MPs from the water column (0 – 1000 m) off the Kii Peninsula while implementing measures to minimize airborne contamination, and investigated their vertical distribution.
In July 2024, seawater samples were collected from 12 depth layers using Niskin bottles equipped with a conductivity-temperature-depth (CTD) profiler. The analysis revealed that S-MP concentrations peaked at a depth of 150 m. The vertical transport of MPs is likely influenced not only by biological processes but also by water mass structure (Liu et al., 2020). Additionally, previous studies have reported that low-salinity water masses of Oyashio origin migrate southward and intrude into the mid-depth layer (200–800 m) off the southern coast of Japan (Yang et al., 1993). Our salinity profile analysis identified a low-salinity water mass between 130 and 200 m, coinciding with the S-MP concentration peak at 150 m. This suggests that the transport S-MPs along with southward Oyashio water in the subsurface layers south of Japan.
In July 2024, seawater samples were collected from 12 depth layers using Niskin bottles equipped with a conductivity-temperature-depth (CTD) profiler. The analysis revealed that S-MP concentrations peaked at a depth of 150 m. The vertical transport of MPs is likely influenced not only by biological processes but also by water mass structure (Liu et al., 2020). Additionally, previous studies have reported that low-salinity water masses of Oyashio origin migrate southward and intrude into the mid-depth layer (200–800 m) off the southern coast of Japan (Yang et al., 1993). Our salinity profile analysis identified a low-salinity water mass between 130 and 200 m, coinciding with the S-MP concentration peak at 150 m. This suggests that the transport S-MPs along with southward Oyashio water in the subsurface layers south of Japan.