Is low frequency ocean sound increasing globally?

Jennifer L Miksis-Olds,Stephen M Nichols

doi:10.1121/1.4938237

Abstract

Low frequency sound has increased in the Northeast Pacific Ocean over the past 60 yr [Ross (1993) Acoust. Bull. 18, 5-8; (2005) IEEE J. Ocean. Eng. 30, 257-261; Andrew, Howe, Mercer, and Dzieciuch (2002) J. Acoust. Soc. Am. 129, 642-651; McDonald, Hildebrand, and Wiggins (2006) J. Acoust. Soc. Am. 120, 711-717; Chapman and Price (2011) J. Acoust. Soc. Am. 129, EL161-EL165] and in the Indian Ocean over the past decade, [Miksis-Olds, Bradley, and Niu (2013) J. Acoust. Soc. Am. 134, 3464-3475]. More recently, Andrew, Howe, and Mercer's [(2011) J. Acoust. Soc. Am. 129, 642-651] observations in the Northeast Pacific show a level or slightly decreasing trend in low frequency noise. It remains unclear what the low frequency trends are in other regions of the world. In this work, data from the Comprehensive Nuclear-Test Ban Treaty Organization International Monitoring System was used to examine the rate and magnitude of change in low frequency sound (5-115 Hz) over the past decade in the South Atlantic and Equatorial Pacific Oceans. The dominant source observed in the South Atlantic was seismic air gun signals, while shipping and biologic sources contributed more to the acoustic environment at the Equatorial Pacific location. Sound levels over the past 5-6 yr in the Equatorial Pacific have decreased. Decreases were also observed in the ambient sound floor in the South Atlantic Ocean. Based on these observations, it does not appear that low frequency sound levels are increasing globally.

Highlights

The observed increasing trends in both the Pacific and Indian Oceans have been attributed, in part, to increases in noise produced by shipping (Andrew et al, 2002; McDonald et al, 2006; McKenna et al, 2012; Frisk, 2012; Miksis-Olds et al, 2013), yet decreases of sound levels in the Northeast Pacific were observed as shipping activity continued to rise (Andrew et al, 2011; Wilcox et al, 2014) Recent observations of the prevalence of seismic airgun activity in the Atlantic Ocean has increased the awareness of this source type and its increasing contribution to the ocean soundscape (Klinck et al, 2012; Nieurkirk et al, 2012)
This study examined decadal trends in ambient sound levels in the South Atlantic and Equatorial Pacific Oceans for comparison to the trends identified in the Northeast Pacific and Indian Oceans (Ross, 1993, 2005; Andrew et al, 2002; McDonald et al, 2006; Chapman and Price, 2011; Miksis-Olds et al, 2013, 2014)
Recordings from the CTBTO IMS hydrophone triads deployed on opposite sides of Wake Island (H11) in the Equatorial Pacific, Ascension Island (H10) in the South Atlantic Ocean, and Diego Garcia (H08) in the Indian Ocean were made available by the AFTAC/US NDC (Air Force Tactical Applications Center/U.S National Data Center) (Fig. 1)

Summary

Introduction

Low frequency (10–100 Hz), deep water ambient sound levels in the Northeast Pacific Ocean have increased at approximately 3 dB/decade (0.55 dB/yr) up until the 1980s (Ross, 1993, 2005; Andrew et al, 2002; McDonald et al, 2006) and slowed to 0.2 dB/yr (Chapman and Price, 2011). This study examined decadal trends in ambient sound levels in the South Atlantic and Equatorial Pacific Oceans for comparison to the trends identified in the Northeast Pacific and Indian Oceans (Ross, 1993, 2005; Andrew et al, 2002; McDonald et al, 2006; Chapman and Price, 2011; Miksis-Olds et al, 2013, 2014). Data from the Comprehensive Nuclear-Test Ban Treaty Organization International Monitoring System (CTBTO IMS) were analyzed from recording locations off Ascension Island (South Atlantic) and Wake Island (Equatorial Pacific). Neither of these locations is located in near proximity to any major shipping lanes.

Methods

Results

Discussion

Conclusion