Directivity of Underwater Sounds Generated in the Vicinity of Tidewater Glaciers

Abstract:

Progressive climate shifts are particularly pronounced in the Polar Regions, including glacial fjords and bays. Many different tools are now widely used to investigate the rate of glaciers’ movement, intensity of calving events and subglacial freshwater outflows or changes in an ice concentration at the sea surface. However, harsh polar conditions make the most of them difficult to conduct and temporal and spatial resolution is often unsatisfactory. Therefore, there is a growing need to develop new methods for quantifying glacier processes. Recently, the application of passive marine acoustics has proved to be promising in this field. Here measurements of ambient noise field directionality made during summer 2013 and spring 2014 in different locations in the Hornsund Fjord, Spitsbergen are presented and discussed. Field data were collected from an inflatable boat using floating buoy equipped with two omnidirectional broadband hydrophones mounted on a horizontal axis, tilt sensor and magnetic compass. A few hours of recordings were analyzed and time differences of arrivals were calculated to obtain directions to the sound sources. The results not only confirm previous observations that underwater sounds in the Hornsund fjord propagates from various directions in distinct spectral bands. They primarily reveal that determined arrival angles together with calculated noise spectral intensity may provide valuable information about the activity of individual glaciers and the distribution of melting glacial ice across the Arctic fjord. Thereby, the applicability of ambient noise oceanography in the study of tidewater glaciers is clearly shown. This work has been supported by the Polish National Science Center grants nos. 2011/03/B/ST10/04275 and 2013/11/N/ST10/01729, Office of Naval Research, Ocean Acoustics Division, grant no. N00014-1410213, and the statutory activity of the Institute of Geophysics Polish Academy of Sciences.