High‐frequency internal wave observations in the marginal ice zone

Abstract

Three thermistor chains extending from 15 to 65 m were deployed from ice floes in the Marginal Ice Zone north of Svalbard in a triangle with sides of 500–800 m for a period of 7 days. Vertical displacement spectra indicate that the internal wave energy level is lower than the Garrett and Munk spectrum by a factor of 2–3 but higher than other observations in the Arctic. A group of internal waves (a wave train), with frequency of 2–3 cph was observed to propagate at 0.05 m/s through the triangle in a west‐southwesterly direction during a 4‐ to 6‐hour period. A case study of this wave train, where the horizontal phase differences between the three thermistor chains were analyzed, showed wavelengths of 100–200 m and phase velocities of 0.10–0.15 m/s. Observation of the density field and the velocity field indicated that stratification dominated over vertical shear. Consequently, the dispersion relation was calculated by solving numerically the vertical mode equation for internal waves in a shearless ocean. The estimated wavelengths and phase velocities agree with the dispersion relation for first‐mode internal waves. The generating mechanisms may be tidal oscillations associated with a seamount located east of the triangle, or ice keels moving in relation to the water creating lee waves in the pycnocline.