In-situ observation of particle size distribution of suspended particles in seawater in the shelf region off Miyagi, Fukushima and Ibaraki Prefectures

Kaeriyama, Hideki*; Furuichi, Naoki*; Sugimatsu, Koichi*; Otosaka, Shigeyoshi  

In order to overview the distribution of suspended particles near the coastal seafloor, an in-situ analyzer of particle size distribution was deployed in the coastal area (100 200 m depth) of Miyagi, Fukushima and Ibaraki Prefectures in September 2017 and June-July 2018. In the observation in September 2017, as a whole, maxima of suspended particle concentration were observed in the subsurface layer (around 40 m in depth) and above the seabed. In the subsurface layer, relatively coarse particles with a particle size of 74 - 330 m was predominant. This layer corresponded with the peak depth of the chlorophyll fluorescence intensity, and it was inferred that the coarse particles were derived from phytoplankton. Seawater near the seafloor contained fine particles with a grain size of 3.78 - 63 m was dominant while coarser particles as observed in the subsurface layer were also observed near the seabed in some shelf-edge stations. It was suggested that particles carried from the surface layer tend to retain in the bottom water of the shelf margin.