The Role of Jets on Mixing Across the Continental Shelf Break of West Antarctica

We use both quasigeostrophic and primitive equation models at high resolution to study what controls this mixing across the continental shelf break of West Antarctica. The model geometry is an idealized channel representing the ACC and interacting with a sloping shelf topography. Results show that there are essentially three regimes controlling the mixing according to the width of the continental shelf break: (1) for very sharp shelves, mixing is continuous and no jet is observed on the shelf break, (2) for intermediate widths, a very strong and stable jet is observed on the shelf break, but becomes periodically unstable (leading to major mixing events), and (3) for wide shelves, a multiple jets regime is observed and mixing is very weak. Surprisingly, mixing is strongest for intermediate widths, where a stable jet (that suppress mixing) is observed for long periods of time. An argument invoking the link between vertical shear and mixing is used to explain this counter-intuitive result. Experiments using a sinusoidal shelf break were also carried out. These show a behavior similar to that described above in the very long and very short shelf break wavelength limits. However, the jet formation can be totally suppressed when the wavelength of the shelf break corresponds to the typical size of an eddy.