Underwater acoustic measurements in northern sea ice covered coastal regions

Abstract

Sea ice cover regulates the interactions between the atmosphere and the ocean in polar regions which in turn affects the underwater soundscape. As sea ice cover declines with the changing climate, the sound it generates, and its impact on sound propagation in the water column will be modified. The decline in sea ice cover will also affect how humans contribute to the soundscape by changing how we travel and access the ocean, whether on the sea ice or by water. This project uses passive acoustic sensors to understand how sea ice affects underwater ambient noise in two northern coastal regions. Data from a real-time acoustic observatory were used to evaluate the seasonal cycle and frequency trends in ambient noise in the Northwest Passage. Cross-correlation and linear regression were used to assess the strength and nature of the inferred relationships between forcing mechanisms and noise levels. The analysis considers the interactions and contributions of wind, ocean currents and ice. A vertical array of hydrophones deployed from sea ice recorded the underwater sound of a snowmobile travelling on sea ice in Nunatsiavut. This project determined that the ice-coupled sources of the snowmobile generate the majority of its underwater sound. An underwater source level was calculated to determine the contribution from snowmobile noise to the underwater soundscape in Postville and Hopedale, NL. A seasonal ice observatory was established in Postville during the 2024 landfast ice season. The observatory measured various atmospheric, ice, and ocean properties using ice-deployed measurement systems such as wind speed, atmospheric temperature, bottom pressure, snow depth, and underwater sound levels. This project combines environmental data measured at the observatory with hydrophone measurements to understand the contribution of ice cracking and saltation to significant acoustic events detected in the ambient sound field. Contributions from saltation noise dominate the beginning of the landfast ice season. Then, thermal ice cracking and motion-based cracking with the influence of the tides dominate acoustic events in the middle of the winter. Finally, high frequency cracking sounds are associated with ice melting at the end of the landfast ice season.