How a Small Reef in the Kuroshio Cultivates the Ocean
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.
[Plain Language Summary]
Vertical nitrate fluxes associated with flow-topography interactions around a small reef in the Kuroshio Current are quantified using state-of-the-art oceanographic instruments. When the flow passes over a shallow sill on the flank of the reef, the velocity differences between layers intensify, resulting in a substantial vertical overturning and mixing of the water column. This turbulent mixing causes the observed nitrate flux from deep water to reach a value among the highest observed worldwide.
• Flow separations and trains of Kelvin-Helmholtz billows mix the water column around a small reef in the Kuroshio
• Doming of isopycnals/nitraclines suggests strong upwelling in the lee of the reef
• Turbulent nitrate fluxes reach up to O(10^3 mmol m^−2 day^−1)続きを見る