Six years of low-frequency underwater noise off the Oregon coast from the OOI Regional Cabled Array System (RCA) and interpretive linkage with RCA Oceanographic Data

Abstract

Approximately 6 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 acoustic 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 the analysis limit to less than 100 Hz. Seasonal warming results in a highly repeatable annual change in the levels at shipping frequencies (50–70 Hz) of order 4 dB which is out-of-phase with concurrent observations of shipping density. Using data from the shallow-water profiler (RCA station SF03A) the influence seasonal warming on the acoustic observations are studied. It is shown how higher ocean surface temperatures cause mode excitation support to move deeper and away typical ship source depths resulting in less efficient transmission of underwater sound. Deviations in the seasonal trends are also observed and shown to be correlated to atypical climatic events such as the warm water blob event of 2015–2016, and suppressed shipping activity during economic downturns, such as observed during COVID-19.