Connecting Mixing to Upwelling Along the Ocean's Sloping Boundary

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Abstract
Deep‐ocean upwelling, driven by small‐scale turbulence, plays a key role in climate by regulating the ocean's capacity to sequester heat and carbon. Recent theoretical studies have hypothesized that such upwelling may primarily occur within a bottom boundary layer (BBL) along the sloping seafloor. A dye experiment in a continental‐slope canyon during the BLT‐Recipes program revealed very rapid BBL‐focussed upwelling, endorsing this notion. Here, we elucidate the dynamical connection between the mixing and the upwelling. We show that along‐canyon upwelling stems from episodic turbulent mixing cells up to 250 m high, generated by tides sweeping up‐ and down‐canyon. The tidal currents support a vertical shear that periodically advects dense waters over slower‐flowing lighter waters, reducing BBL stratification. This triggers instabilities that mix the dense waters with neighboring lighter waters, resulting in net along‐boundary upwelling. Our findings substantiate the view that deep‐ocean upwelling can predominantly occur along the ocean's sloping boundaries.
Funding Information
  • Natural Environment Research Council (NE/S001433/1)
  • National Science Foundation (1756264)
  • National Science Foundation (1756324)
  • Office of Nuclear Energy

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