Observations of ducting of acoustic energy in the Fram Strait.

Arctic areas like the Beaufort Sea are commonly characterized by the formation of sub-surface acoustic ducts. Conversely, the eastern Arctic is known for its upward refracting propagation environment, which creates surface ducts. Using moored passive acoustic recorders in the Fram Strait in the eastern Arctic Ocean, we measured the average distribution of sound energy in the water column. The moorings were deployed by the CMRE Environmental Knowledge and Operational Effectiveness program and instrumented with several oceanographic sensors and acoustic recorders. Even though some acoustic recorders failed to record for the entire experiment, we characterized the vertical distribution of the ambient noise field. We measured the formation of temporary sound energy duct-type areas in the thermocline. Using Copernicus Marine service data, we investigated the effects of the sea ice concentrations, sea ice drift and distance to the sea ice edge on the vertical distribution of ambient noise. The distance from the ice edge had a negative correlation with sounds levels, while ice drift and concentration were not correlated to the overall sound levels. Simultaneous sound speed measurements revealed the presence of potential sound channels. We investigated the possible origin of the sound energy, and the formation of potential sub-surface ducts, applying range-dependent sound propagation modelling coupled with high-resolution output of the double nested CMRE’s Pan-Arctic ocean-sea ice model.