  This study describes a specific type of critical layer for near-inertial
waves (NIWs) that forms when isopycnals run parallel to sloping bathymetry.
Upon entering this slantwise critical layer, the group velocity of the waves
decreases to zero and the NIWs become trapped and amplified, which can enhance
mixing. A realistic simulation of anticyclonic eddies on the Texas-Louisiana
shelf reveals that such critical layers can form where the eddies impinge onto
the sloping bottom. Velocity shear bands in the simulation indicate that
wind-forced NIWs are radiated downward from the surface in the eddies, bend
upward near the bottom, and enter critical layers over the continental shelf,
resulting in inertially-modulated enhanced mixing. Idealized simulations
designed to capture this flow reproduce the wave propagation and enhanced
mixing. The link between the enhanced mixing and wave trapping in the slantwise
critical layer is made using ray-tracing and an analysis of the waves'
energetics in the idealized simulations. An ensemble of simulations is
performed spanning the relevant parameter space that demonstrates that the
strength of the mixing is correlated with the degree to which NIWs are trapped
in the critical layers. While the application here is for a shallow coastal
setting, the mechanisms could be active in the open ocean as well where
isopycnals align with bathymetry.
