[A-OS15] Ocean circulation and material cycle in coastal seas

[AOS15-08] Behavior of suspended particulate matter and Bottom boundary layer processes off Fukushima Prefecture

*Naoki Furuichi¹, Hideki Kaeriyama², Koichi Sugimatsu¹ (1.Fisheries Technology Institute, Japan Fisheries Research and Education Agency , 2.Fisheries Research Institute, Japan Fisheries Research and Education Agency )

Keywords:particulate matter dynamics, bottom boundary layer, turbulence, particle size distribution

Sediment matter suspension and dispersion processes are thought to play important roles in forming marine benthic ecosystems, including those of demersal fishes. We investigated the behavior of suspended particulate matter on the shelf slope areas off Fukushima, focusing on the relationships with bottom boundary layer (BBL) processes, based on field observations and numerical simulations. Field observations were conducted using Laser In-Situ Scattering and Transmissometry (LISST)-100X/200X in the coastal region off Fukushima and nearby prefectures, and the vertical profiles of the volumetric concentration of particles and particle size distribution were obtained. The observations showed that the volumetric concentration of particles near the seabed increases considerably at many stations located near shelf slopes, where the total water depth is 100–200 m. We frequently observed that particles with a radius of less than 100 µm were dominant in this high turbidity layer; BBL thickness ranged from 10–100 m, and the volumetric concentration decreased significantly above the BBL compared to that within the BBL. To understand the mechanism behind the observed results, we conducted a vertical one-dimensional numerical experiment on tidal BBL processes and particulate matter behavior. The experiments demonstrated that the tidal current efficiently developed the BBL and that the vertical distribution of particle concentration was strongly controlled by the balance between tide-induced turbulent mixing and the settling of particles. These results suggest that BBL thickness and turbulence processes are important factors determining the distribution of particulate matter concentration.