Temporal and spatial characteristics of the Beaufort Sea ambient noise environment

Underwater ambient noise from the Beaufort Sea, collected in March 2016, is analyzed to investigate the effect that environmental changes in the region have on the spatial and temporal characteristics of the ice-generated ambient noise. In particular, the influx of warm Pacific water, so called the Beaufort Lens, has dramatically altered the level and vertical directionality of ambient noise, creating a low noise zone in the ∼75-250 m depth interval with a noise notch at low grazing angles. It is also demonstrated how the observed noise vertical directionality is consistent with ice-mechanical activity along an active pressure ridge ∼30-50 km from the recording array, as shown by satellite imagery. The discrete ranges to this ice activity explain the peak arrival angles between -10 to -15 degrees in noise vertical directionality, as well as the horizontal noise notch. Transient noise events associated with the ice activity are analyzed using an image processing approach with hierarchical clustering applied to the recorded spectrograms. The observed events are grouped into three categories-short-time-broadband, long-time-narrowband, and long-time-broadband-each likely generated through a different mechanism by the ice cover. The spectral and temporal distribution of these transients are discussed.