Low-frequency ocean acoustics – measurements from the Lofoten-Vesterålen Ocean Observatory, Norway

This paper will focus on acoustic measurements from the Vesterålen cabled ocean observatory, located 15 km offshore northern Norway, at a depth of 255 m. The measurements were made with a calibrated Ocean Sonic hydrophone SB35-ETH, recording since 2013. The hydrophone node is located in a large (ca. 15 km) canyon, not far from shipping lanes. We have measured acoustic variability up to the third-octave band centered on 125 Hz, the second shipping band identified in the European Marine Strategic Framework Directive (MSFD). Time scales from months (spanning several seasons across 2018) to hours have been investigated, considering broadband Source Pressure Levels (SPL, between 1--125 Hz), SPLs over 1-Hz frequency bands (to identify variability within third-octave bands and associate them with potential sources), and percentile contributions over the different frequency bands. Sounds from shipping and fin whale vocalisations are important contributors. Early analyses show it is also possible to detect sounds from far-away earthquakes apparently propagating in the water column (e.g. an mb = 4.9 event in the Jan Mayen Fracture Zone, 830 km away), and other noise sources over ranges of up to 2212 km.