How a Small Reef in the Kuroshio Cultivates the Ocean

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.