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Microstructure and Mooring Observations of Enhanced Mixing in the Kerama Gap
Author(s) -
Inoue Ryuichiro,
Tanaka Takahiro,
Nakamura Hirohiko,
Yanagimoto Daigo,
Fujio Shinzou,
Yasuda Ichiro
Publication year - 2020
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2019jc015553
Subject(s) - sill , geology , mixing (physics) , mooring , seafloor spreading , internal tide , oceanography , turbulence , thermal diffusivity , eddy diffusion , internal wave , atmospheric sciences , mechanics , petrology , physics , quantum mechanics
Abstract Microstructure and mooring observations were conducted around the Kerama Gap, near the midpoint of the Ryukyu Island chain, in December 2016. We observed enhanced mixing near raised seafloor topography with vertical diffusivity from 10 −2 to 10 −1 m 2 s −1 in the bottom water and found that tides were important drivers of enhanced mixing above sills. Two‐dimensional numerical simulations of a vertical cross section of the Kerama Gap indicated that breaking internal tides play an important role in the enhanced mixing behind the sill near the entrance to the gap. In addition, M2 internal tides radiating from the sills at the gap's entrance and exit may correspond to the observed enhanced vertical shear and mixing around the salinity minimum layer of the North Pacific Intermediate Water (NPIW) in the Kerama Gap. Simple quantitative arguments based on the observed turbulence data suggest that the enhanced mixing at the sill may influence the renewal of the bottom water and the NPIW in the Okinawa Trough, about 10% of required fluxes in the Kerama Gap estimated in past studies, indicating its importance on the distributions of water masses and water properties in the North Pacific.