On the modification of tides in a seasonally ice-covered sea

New observations from eight moorings located in Foxe Basin, Hudson Strait, and Hudson Bay are used to study the seasonal variability of the M-2 tide. Significant seasonal variations of the M-2 surface elevation are found in all these regions and at all seasons. The largest variations occur during winter while both elevation increase (Hudson Strait) and decrease (Hudson Bay, Foxe Basin) are observed. These variations are found recurrent at the stations where multiyear observations are available. Observations from a velocity profiler are consistent with a seasonal damping of the tides because of friction under ice. Numerical simulations with a sea ice-ocean coupled model and realistic forcing qualitatively reproduce most of the features of the observed variability. The simulations show that the winter M-2 variations are essentially caused by the under-ice friction, albeit with strong regional differences. Under-ice friction mostly occurs in a limited region (Foxe Basin) and can account for both increased and decreased M-2 elevations during winter.