Semi-diurnal oscillations are a ubiquitous feature of polar sea-ice motion. Over much of the Arctic basin, inertial and semi-diurnal tidal variability have similar frequencies so that periodicity alone is inadequate to determine the source of oscillations. We investigate the relative roles of tidal and inertial variability in Arctic sea ice using a barotropic ice–ocean model with sea ice embedded in an upper boundary layer. Results from this model are compared with ‘levitated’ ice–ocean coupling used in many models. In levitated models the mechanical buoyancy effect of sea ice is neglected so that convergence of ice, for example, does not affect the oceanic Ekman flux. We use rotary spectral analysis to compare simulated and observed results. This helps to interpret the rotation sense of sea-ice drift and deformation at the semi-diurnal period and is a useful discriminator between tidal and inertial effects. Results indicate that the levitated model generates an artificial inertial resonance in the presence of tidal and wind forcing, contrary to the embedded sea-ice model. We conclude that sea-ice mechanics can cause the rotational response of ice motion to change sign even in the presence of strong and opposing local tidal forcing when a physically consistent dynamic ice–ocean coupling is employed.
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