Abstract
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 10–800 Hz in 2017–2018 and 10–6400 Hz in 2018–2019. Co-located measurements of ice draft, salinity, temperature, and current profiles, along with nearby meteorological measurements, provide time series of environmental forcing and conditions. An updated seasonal baseline for ambient noise in Barrow Strait is calculated and compared against historical measurements, along with a review of noise-generating mechanisms and transmission loss models in the Arctic.
Highlights
The Arctic Ocean is the northernmost body of water in the world and features constant ice cover, causing temperature and salinity profiles unlike any other ocean basin
To help distinguish the sources of noise that might contribute to the ambient noise, the Arctic Ocean can be divided into four different regimes (Carey and Evans 2011): 1. The central Arctic: permanently covered with pack ice 2
A Monte Carlo simulation study driven by historical observations showed that when a vessel was within the study region, the Tallurutiup Imanga National Marine Conservation Area (TINMCA), the 24-h sound exposure level predicted that vessel noise would be audible to narwhals, belugas, and bowheads for 85%, 81%, and 88% of the time, respectively, but never above the National Oceanic and Atmospheric Administration’s limit of temporary threshold shift, where temporary hearing loss will occur (NMFS 2018)
Summary
The Arctic Ocean is the northernmost body of water in the world and features constant ice cover, causing temperature and salinity profiles unlike any other ocean basin These unique profiles keep cool freshwater at the surface and, together, generate a unique sound speed profile which has a positive gradient with increasing depth causing horizontally propagating sound waves to be refracted towards the surface. The mechanisms of natural ambient noise generation must be understood in order to accurately model and predict the background against which increasing the sounds of anthropogenic activity (noise pollution) will be added to the marine habitat. Recent work on the use of permanent monitoring systems for the real-time reporting of ambient noise is presented
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