Tidal effects on the circulation under the ice shelves and ice shelf melting in the Amundsen Sea were investigated using a numerical model, through comparison of simulations with and without tides. In the Amundsen Sea, tidal impacts were dependant on the location of the ice shelf front with respect to the M2 effective critical latitude. The critical latitude is the latitude where the tidal frequency equals the inertial frequency. The effective critical latitude is where the tidal frequency equals the inertial frequency adjusted by relative vorticity, such as that associated with a wind-driven gyre. For ice shelves located equatorward of the M2 effective critical latitude, tides increased both mixing in front of and under the ice shelf and flow into the ice shelf cavities by as much as 50%, despite weak tides compared with the mean flows. Tides also increased melting for these ice shelves by 1–3.5 m yr−1, a 50% increase for Dotson Ice Shelf and 25% for Pine Island Ice Shelf. These enhancements were not a result of tidal residual flows, but instead originated from resonant effects, increases in the baroclinity of the velocities, and higher mixing, all of which are associated with critical latitude effects on internal tides. For ice shelves located poleward of the effective critical latitude, tides very slightly retarded flow into the cavity and slightly reduced melting.