An experimental model of wave attenuation in pancake ice

In the winter, when the Antarctic sea ice cover is expanding, the far edge of the marginal ice zone is populated by small floes with characteristic diameters much smaller than ocean wavelengths and known as pancake ice. This form of sea ice was once only typical of Antarctic waters, but it is now observed in the Arctic due to the intensification of the wave action following ice retreat. Despite recent studies, the governing physics controlling how waves propagate through pancake ice is not understood. To cast new light on the propagation of waves in ice. an experimental model was setup in the Sea Ice Wind Wave Interaction (SIWWI) flume at the University of Melbourne, which allows operations at sub-zero temperatures. To simulate pancakes, the ice cover was modelled using ice cubes with characteristic dimension of a few centimeters (much smaller than the generated wavelength) and different concentrations. Experiments consisted of tracking the propagation of regular and irregular wave fields along the flume to monitor the dissipative effect of the ice cover. Results indicate that wave attenuation depends on ice concentration, with as low as 20 - 40% of energy going through high density covers. Although observations reveal that the ice cover attenuates wave energy over the entire spectrum, energy attenuation is more effective at high frequencies, inducing a significant downshift of the spectral peak.