Observations of Wind-Generated Waves in Antarctic Fast Ice

Abstract

Observations of naturally induced propagating waves in the fast ice cover of McMurdo Sound, Antarctica, were made during the austral winter of 1986 with a rosette of three wire strainmeters. The data, collected over a seven-month period and including a wide range of ice conditions and wind velocities, constitute a winter wave climatology, and show for the first time the nature and magnitude of flexural-gravity waves induced by the direct action of turbulent air flow over the ice surface. It is observed that below a threshold wind velocity, corresponding roughly to the minimum group velocity for wave propagation in the ice (≈10 m s?1, no resolveable waves are produced. At wind speeds above the threshold, wave energy increases significantly with increasing wind velocity. Analyses of the wave-energy density spectra show the observed wave characteristics to be in general agreement with existing theory, although considerable scatter in the data prevents detailed comparisons. The absolute magnitudes of the observed strains were roughly one order of magnitude below the theoretical fracture strain for sea ice, indicating that over the relatively thick ice encountered in this study, wind generated waves alone are unlikely to cause fracturing; however over thinner ice, or in combination with wind stress or ocean swell, they may play an important role in the breakup of fast ice sheets.