Tidal vertical mixing beneath Filchner-Ronne Ice Shelf

High Salinity Shelf Water (HSSW) flowing into the cavity beneath Filchner-Ronne Ice Shelf (FRIS) occupies the lower portion of the water column. Tidal mixing is likely to be a primary mechanism for mixing HSSW up through the water column, where it is transformed through melting at the underside of the ice shelf into Ice Shelf Water (ISW), a precursor of Antarctic Bottom Water (AABW). Beneath the ice shelf, frictional stress influences tidal currents not only at the seabed but also at the ice shelf base, inducing vertical mixing. In deep water regions of the ice shelf cavity with slow tidal currents, the frictional boundary layers occupy a small fraction of the water column but in shallow regions they could occupy the entire water column and dominate the tidal dynamics. Furthermore, the northern portion of FRIS lies close to 74°28' S, the critical latitude for the M2 tidal constituent. At this latitude the inertial or Coriolis frequency ( f ) equals the M2 tidal frequency (ω) resulting in a strong depth-dependent tidal current with thick boundary layers that increase as the critical latitude is approached [Furevik and Foldvik, 1996]. As boundary layers are usually turbulent, vertical mixing is likely to be enhanced near the critical latitude. The work presented here is concerned with the influence of polarisation of the tidal current ellipse on vertical mixing in the stratified, sub-ice shelf water column. The polarisation range’s from a purely circular clockwise current, through a flat or degenerate ellipse, to a purely circular anticlockwise current.

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