Abstract
The ocean soundscape of the Gulf of Mexico (GOM) has not been well-studied, although it is an important habitat for marine mammals, including sperm and beaked whales, many dolphin species, and a potentially endangered baleen whale species. The GOM is also home to high levels of hydrocarbon exploration and extraction, heavily used commercial shipping ports, and significant fishery industry activity, all of which are known contributors to oceanic noise. From 2010-2013, the soundscape of three deep and two shallow water sites in the GOM were monitored over 10 - 1000 Hz. Average sound pressure spectrum levels were high, >90 dB re 1 μPa(2)/Hz at <40 Hz for the deep water sites and were associated with noise from seismic exploration airguns. More moderate sound pressure levels, <55 dB re 1 μPa(2)/Hz at >700 Hz, were present at a shallow water site in the northeastern Gulf, removed from the zone of industrial development and bathymetrically shielded from deep water anthropogenic sound sources. During passage of a high wind event (Hurricane Isaac, 2012), sound pressure levels above 200 Hz increased with wind speed, but at low frequencies (<100 Hz) sound pressure levels decreased owing to absence of noise from airguns.
Highlights
Ocean soundscapes have both anthropogenic and natural sources, and often vary across frequencies, locations, and time-periods (Hildebrand 2009)
During 2010–2013, five high-frequency acoustic recording packages (HARPs) sampling at 200 kHz continuously were deployed for 2–9 months per deployment in the Gulf of Mexico (GOM) at sites with names based on the Bureau of Ocean Energy Management (BOEM) lease blocks in which the sites were located: Green Canyon (GC), Mississippi Canyon (MC), Main Pass (MP), DeSoto Canyon (DC), and Dry Tortugas (DT) (Fig. 1; Table I)
The hydrophones were composed of two channels, one for low-frequency (2 kHz), we focus on only the low-frequency band for this paper
Summary
Ocean soundscapes have both anthropogenic and natural sources, and often vary across frequencies, locations, and time-periods (Hildebrand 2009). At a deep-water site in the northeastern Pacific it was shown that sound pressure spectrum levels at 40 Hz have increased about 3 dB per decade over the last 40 yr, attributed primarily to an increase in commercial shipping and to the site’s deep-water exposure to the Pacific Ocean basin (McDonald et al, 2006). For approximately 1 month in 2001 in the northern GOM, Newcomb et al (2002) recorded similar sound pressure spectrum levels using similar equipment to Snyder (2007), at shallower depths on the continental slope at 600–1000 m.
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