Near-inertial current oscillations with 10--20cm/s amplitudes were prevalent over the Bering Sea shelf during November 1982 and again in March and April 1983 and also evident at reduced amplitudes during the intervening winter. Spectral peak frequencies were consistently within ~1% of the local inertial frequency f, in constrast to the more superinertial (~5% above f) frequencies commonly reported elsewhere. A superinertial secondary energy peak at 1.038f was evident, corresponding to the first-mode wave. Amplitudes decreased with distance shoreward from the shelf break, consistent with the effects of decreasing bottom depth and increasing mixed layer depth. The oscillations were highly coherent over ~100 km distances, similar to observations reported by Thomson and Huggett (1981) for the British Columbia coast, whereas near-inertial oscillations have been commonly reported to be uncoupled over much shorter (~10 km) distances in other regions. Vigorous near-inertial ''ringing'' was associated with rapidly passing weather systems. The decline in near-inertial oscillation amplitudes during winter was partially due to a siginificant reduction in both cyclone frequency and occurence of wind events causing clockwise wind shifts.

The decline was enhanced by reduction in the vertical stratification needed to support inertio-gravity internal waves, as the shelf waters apparently became mixed from top to bottom. The loose, mobile sea ice in the winter marginal ice zone (MIZ) did not appear to inhibit wind generation of the inertial oscillations. The presence of sea ice appears, in fact, to have contributed to the spring increase of near-inertial current amplitudes through restratification of the water column caused by melting ice. Our observations, particularly the spatial coherency and spectral properties, were generally consistent with Kundu and Thomson's (1985) model for inertio-gravity waves generated in the wake of a translating weather front. The half wavelength typical of these waves forced by transiting weather fronts on the Bering shelf appears to be ~150 km, or approximately the width of the winter MIZ. The associated near-inertial currents are 180¿ out of phase with those a half wavelength away in the direction of phase propagation. Thus a storm passing perpendicular to the ice edge can excite waves at near-inertial frequencies which compress, deform, and dilate the ice pack by up to a few percent of the MIZ width. We suggest that this mechanism, in conjunction with near-inertial interfacial shear which can increase upward heat flux, influences the width scale of the MIZ. ¿ American Geophysical Union 1987