Acoustic properties of Arctic sea ice, from year-long underwater measurements in Cambridge Bay, Canada

The Arctic environments are fragile and undergoing rapid changes. Their underwater signatures are measured with Passive Acoustic Monitoring (PAM) . Autonomous recorders and ocean observatories now enable the measurement of extremely large time-series, ranging from seconds to years and ultimately decades. Their analyses can in turn inform management of the different Arctic regions, working toward compliance with UN Sustainable Development Goal SDG-14. A key component of Arctic environments is sea ice, whose extent decreased by 30%, with predictions of an ice-free Arctic summer within the next decade(s).
This study focuses on the seafloor observatory in Cambridge Bay (Canada) operated by Ocean Networks Canada (ONC). Shallow-water ambient sound is supplemented with ice draft measured above the hydrophone, air temperature and salinity from a shore station (all operated by ONC). Ice cover/type are provided by satellite charts from the Government of Canada Ice Archive, using the WMO Egg Code. The period of analysis spans August 2018 to May 2019, including free-water and ice-covered seasons.
PAMGuide (Merchant et al., 2015) provided broadband Sound Pressure Levels (SPLs), Third-Octave band Levels (TOLs), Power Spectral Densities (PSDs) and percentile contributions up to 32 kHz. Acoustic events are identified using their broadband SPL relative to the background noise and their respective durations. Frequency analyses show bimodal peaks in the 200 and 800 Hz bands in the winter months, with monthly averaged levels 20 dB above background. Based on comparison with previous studies of ice noise, these are associated with thermal ice cracking. Daily broadband noise increases as temperature increases, confirming quieter periods during ice cover. The number of transient ice events correlates with colder temperatures and increased daily temperature variation. This investigation found ice noise in Cambridge Bay, an area of land-fast, first-year ice, to be predominantly made of broadband transients, with frequencies concentrated below 1 kHz.