[A-OS14] Coastal physical processes associated with mixing, eddies, internal waves

[AOS14-01] Enhancement of turbulent mixing over tidal sandwaves and formation of front: an observational study in Seto Inland Sea

*Eisuke Tsutsumi¹, Xinyu Guo², Naoki Yoshie², Takahiro Endoh³, Takeshi Matsuno³, Sachihiko Itoh¹ (1.Atmosphere and Ocean Research Institute, The University of Tokyo, 2.Center for Marine Environmental Studies, Ehime University, 3.Research Institute for Applied Mechanics, Kyushu University)

Keywords:Flow-seabed interaction, Microstructure turbulence measurement, Tidal mixing front, Seto Inland Sea

It is known that in Iyo-nada, Seto Inland Sea, Japan large sandwaves are formed in the southwest. The generation mechanism of large sandy bedforms has been intensively studied in rivers, estuaries, coastal and shelf seas. However, there has been less attention to how sandwaves affects ocean circulations and environments. In this study, we report on the significant enhancement of vertical mixing by sandwaves from a total of 24 field campaigns consisting of microstructure turbulence and current measurements in Iyo-nada conducted during 2012–2019. We document elevation of turbulence energy dissipation rate to O(1 W m⁻²) over large sandwaves, flow separation at the sandwave crest, and the associated downstream turbulent wakes due to the form drag. This strong turbulence suggests that the turbulent buoyancy flux in the large sandwave region exceeds the surface buoyancy flux, creating a contrast in the vertical mixing regime to the region without sandwaves and promoting the formation of a front between the two regions.