No abstract

In the Arctic, sound levels have historically been strongly tied to sea ice and wind speed, with very little impact of anthropogenic noise. However, climate change is causing a loss of sea ice, and consequently increased ship traffic and anthropogenic underwater noise. Here, we present the first quantitative, comparative analysis of underwater sound levels across the Canadian Arctic. We analyzed 39 passive acoustic datasets collected throughout the Canadian Arctic from 2014 to 2019 to examine spatial and temporal trends in sound pressure levels (SPL), quantify environment drivers of SPL, and estimate the influence of ship traffic on SPL. Daily mean SPL in the 50–1000 Hz bandwidth ranged from 70 to 127 dB re 1 μPa (median = 91 dB). SPL increased as wind speed increased, but decreased as both ice concentration and air temperature increased. The highest SPLs were in August-October, and the lowest in March–April. SPL increased as the number of ships increased. The highest mean SPLs were recorded near southeast Baffin Island, but the most ship noise was recorded near Pond Inlet (>1 ship/day in summer). This study provides an important baseline for underwater sound levels in the Canadian Arctic, and fills many geographic gaps on published underwater sound levels.

The main sources of noise in the Arctic Ocean are naturally occurring, rather than related to human activities. Sustained acoustic monitoring at high latitudes provides quantitative measures of changes in the sound field attributable to evolving human activity or shifting environmental conditions. A 12-month ambient sound time series (September 2018 to August 2019) recorded and transmitted from a real-time monitoring station near Gascoyne Inlet, Nunavut is presented. During this time, sound levels in the band 16–6400 Hz ranged between 10 and 135 dB re 1  μPa2/Hz. The average monthly sound levels follow seasonal ice variations with a dependence on the timing of ice melt and freeze-up and with higher frequencies varying more strongly than the lower frequencies. Ambient sound levels are higher in the summer during open water and quietest in the winter during periods of pack ice and shore fast ice. An autocorrelation of monthly noise levels over the ice freeze-up and complete cover periods reveal a ∼24 h periodic trend in noise power at high frequencies (>1000 Hz) caused by tidally driven surface currents in combination with increased ice block collisions or increased stress in the shore fast sea ice.

Numerous studies of ocean ambient noise and under-ice acoustic propagation and reverberation in the Canadian Arctic have been carried out since the 1960s. These studies, largely led by scientists at the Defence Research Establishment Pacific and Defence Research and Development Canada, have been motivated by the need to improve sonar performance prediction in the Arctic over the wide range of seasonal ice, oceanographic, and meteorological conditions at high latitudes. Aside from the valuable insight into the physics of noise generation by sea ice and sound propagation under sea ice, they provide a historical baseline for Arctic ambient noise against which modern measurements can be compared. In 2017, the Department of Fisheries and Oceans added passive acoustic monitoring to their Barrow Strait Real Time Observatory, reporting power spectral density over the acoustic band of 10

As part of the Sustainable Nunatsiavut Futures project, a field experiment to determine the acoustic properties and underwater radiated sound level of a snowmobile was designed and executed. The fieldwork consists of lowering acoustic recorders under the sea ice and driving a snowmobile with a known position and velocity to evaluate its speed-dependent source level. This experiment is the first step toward collaborative Dalhousie and community research on underwater sound as it relates to the marine habitat, human use of the ocean, and sea-ice in Nunatsiavut. Due to COVID-19, the planning stages were coordinated virtually, and the fieldwork in Nunatsiavut was conducted by local Inuit Research Coordinators (IRCs), while a twin Dalhousie-led experiment was conducted in Caraquet, New Brunswick. A single hydrophone sensor was used in Nunatsiavut, and a vertical array of hydrophones was used in Caraquet to obtain underwater sound data from a moving snowmobile. Skidoo specifications for each site were recorded as well as sea-ice thickness, temperature, salinity, and sound-speed data were collected. Spectrograms of skidoos traveling at different speeds were computed. Comparisons between received levels at different velocities, sites, and ranges are shown, and the impact of sea ice and snowmobile specifications on received levels are discussed.