Under-ice noise in Eastern Beaufort Sea: ice drift forcing, fracturing and formation of leads
Résumé
Eastern Beaufort Sea underwater noise was recorded from September 2005 to October 2006 at two stations, 300 km apart, on Mackenzie shelf break and Amundsen Gulf mouth. The region was ice-covered (> 90%) from November to mid-June. The regional under-ice background ambient noise, from a myriad of undistinguishable sources integrated over large ranges, was estimated daily for 3 acoustic bands and correlated with measured wind, in situ mean currents and large-scale ice speed as potential forcings. Correlations were observed between wind and ice drift, and ice drift and surface layer current. Ambient noise level was correlated with all these three variables. The ambient noise correlation with the large-scale ice drift suggests a connexion with the southern part of the large Beaufort gyre. Ice cracking, shearing and colliding add strong transient events above the general ambient noise level. An example of the opening and closing a ~500-km long lead along the large-scale offshore plume of multiyear ice moving along the shelf, is used to evidence the different types of wideband noise and tones, of variable duration, related to these events. Some tones are repeated with a period corresponding to waves and can sometime be confounded with marine mammal songs. These ice noise events are occurring all along the winter, and the most energetic ones correspond to lead openings.