Seasonal variation of the global low-frequency ocean soundscape from 25 years of NOAA-PMEL hydrophone deployments

Robert P Dziak1, TK Lau2, Haru Matsumoto3, David Mellinger4, Joseph Haxel2, Samara Haver5, Delwayne R Bohnenstiehl6, Jason Gedamke7, Leila Hatch8, Won Sang Lee9, Megan McKenna10, Julie Perrot11, Jean-Yves Royer12 and Deborah K Smith13, (1)NOAA Pacific Marine Environmental Laboratory, Seattle, WA, United States, (2)NOAA Newport, Newport, OR, United States, (3)Oregon State University, CIMRS, Newport, OR, United States, (4)NOAA/OSU Cooperative Institute for Marine Resources Studies, Newport, United States, (5)Oregon State University, CIMERS, Newport, United States, (6)North Carolina State University, Marine, Earth and Atmospheric Sciences, Raleigh, United States, (7)NOAA Fisheries, Office of Science and Technology, Silver Spring, United States, (8)NOAA Office of National Marine Sanctuaries, Scituate, United States, (9)Korea Polar Research Institute, Incheon, South Korea, (10)National Park Service Natural Sounds and Night Skies Division, CO, United States, (11)University of Western Brittany, Brest, France, (12)Univ. Brest / CNRS, Laboratoire Geosciences Ocean, Plouzane, France, (13)National Science Foundation, Arlington, VA, United States
Over the last 25 years, NOAA’s Pacific Marine Environmental Laboratory (PMEL) has collected continuous ambient sound data using calibrated, moored hydrophones deployed throughout the world’s oceans. In total, there have been 349 individual hydrophone mooring deployments within 17 geographic subregions including multiple stations across the U.S. EEZ, the south, equatorial and north Atlantic Ocean, eastern and western tropical Pacific Ocean, as well as sites within the central Indian, Arctic and Southern Oceans. Almost all deployments were associated with ad-hoc geophysical or biological experiments with a variety of U.S. government agency, academic, and international partners. This diversity in research goals enabled global coverage; unfortunately, the majority of the hydrophone deployments were non-contemporaneous. Nevertheless these acoustic records offers one of the more spatially comprehensive views of the variation in global-ocean ambient sound levels. Instrument packages at all stations were built in-house at PMEL with the first prototype deployed in 1995, which further enabled standardized, cross-calibrated measurement comparison.

Overall, our analysis goal was to elucidate consistent seasonal variation in sound levels over the 25-year archive. The 10-45 Hz band was chosen for analysis to maximize overlap in frequency among the many acoustic datasets with varied sample rates. This frequency band is ideal because there are a variety of sound sources in this band, including anthropogenic (shipping, airguns), geophysical (sea-ice, seismo-volcanic), biological (baleen whales), and meteorological (wind-driven wave-noise) sources. We present global maps of sound level distributions at the 50th percentile, in the 10-45 Hz band, derived from the mean from all PMEL hydrophone recordings during each month of the year. We also estimate the spherical and cylindrical sound propagation out to a several hundred km radius around each station to produce a broader scale view of sound transmission in each ocean basin. Each hydrophone was moored at sound channel depths (500-1000 m) to record ambient sound over as large a detection radius as possible.