How a Small Reef in the Kuroshio Cultivates the Ocean
Daisuke Hasegawa, Takeshi Matsuno, Eisuke Tsutsumi, Tomoharu Senjyu, Takahiro Endoh, Takahiro Tanaka, Naoki Yoshie, Hirohiko Nakamura, Ayako Nishina, Toru Kobari, Takeyoshi Nagai, Xinyu Guo
Abstract
Abstract Vertical nitrate fluxes associated with turbulent mixing and upwelling around a small reef in the Kuroshio are quantified by continuously deploying a turbulence microstructure profiler with an attached submersible ultraviolet nitrate analyzer while drifting from the upstream to the downstream of the reef. Flow separations and trains of Kelvin‐Helmholtz billows (thickness = 60 m) are identified using a shipboard ADCP and an echo‐sounder. The turbulence diffusivity associated with the vigorous turbulent mixing reaches up to O (10 −1 m 2 s −1 ), resulting in strong nitrate fluxes of O (1–10 3 mmol m −2 day −1 ). In addition, large differences between the upstream and downstream density profiles suggest a strong upwelling velocity of O (10 −3 m s −1 ), as well as an upwelling nitrate flux of O (10 2 mmol m −2 day −1 ) in the entire subsurface layer.