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Trends in low frequency ambient noise for a site 80 km off the Oregon coast over approximately four years ending August 2020

Approximately 4 years of underwater noise data recorded from the Regional Cabled Array (RCA) network, at the site known as Hydrate Ridge, is studied for purposes of examining long term trends. The data originate from station HYS14 located on the seabed at a depth of approximately 800 m and 80 km offshore of Newport, OR. The sample rate is 200 Hz, setting to the analysis limit to less than 100 Hz. A distinctive feature of the data is the sound pressure level in the frequency range of 20 Hz that reflects the migratory timing of fin whales, which peaks near the start of the new year, and reaches a minimum around June. There is a suggestion that the level between 10 and 70 Hz attributable shipping activity, is reduced in the spring of 2020 by about 2 dB relative the three prior years, possibly owing reducing economic activity linked with Covid-19. At the time of this writing independent verification of with shipping data is ongoing. [This study was partially supported by U.S. Office of Naval Research and by the UW Cooperative Institute for Climate, Ocean and Ecosystem Studies (CICOES).]