Twice a day, sea levels rise and fall with the tides. However, the effects of tidal flow extend beneath the surface. When subsurface tidal flow encounters a big obstacle—like a submarine mountain—large-amplitude waves form, mixing up ocean layers.
Here Winters presents a new three-dimensional numerical simulation of tidal flow over steep slopes and its effects. The calculations could be used to improve models of tidally generated internal waves and enhance scientists’ understanding of the global circulation of ocean water.
The new simulation focuses on the turbulent boundary layer that forms at a steep continental slope. At the edge of the continental shelf, the ocean floor can drop steeply down to the ocean basin. When subsurface tidal flow hits such a slope, the energy of the flow dissipates, and water layers of different densities and temperatures mix. Tidal flow up and down a steep slope also creates internal waves.
This simulation improves on existing models by mathematically accounting for the complexities behind energy dissipation in tidal flow over a steep obstacle.
The author tested his simulation by comparing its predictions to observations from a 2006 study of internal waves in the Bay of Biscay in western Europe. Over several tidal cycles, the simulation generated density, turbulence, mixing, and dissipation effects that closely mirrored those seen in the bay. The simulation also checked out against real-world observations near Monterey Canyon off the coast of California and the Great Meteor Seamount in the Canary Basin.
Scientists have suggested that the mixing that occurs when tidal flow encounters steep slopes plays an essential role in stirring up ocean water on global scales. This mixing connects the deep ocean to the atmosphere and transports heat, salt, nutrients, and other materials.
This new simulation could help pave the way for better models of global ocean mixing and climate change. (Geophysical Research Letters, doi:10.1002/2015GL064676, 2015)
—Sarah Stanley, Freelance Writer
Citation: Stanley, S. (2016), Simulating tidal flow and mixing at steep submarine slopes, Eos, 97, doi:10.1029/2016EO043953. Published on 21 January 2016.