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Wiggins, SM, Leifer I, Linke P, Hildebrand JA.  2015.  Long-term acoustic monitoring at North Sea well site 22/4b. Marine and Petroleum Geology. 68, Part B:776-788.   10.1016/j.marpetgeo.2015.02.011   AbstractWebsite

Marine seeps produce underwater sounds as a result of bubble formation and fragmentation upon emission from the seabed. The frequency content and sound levels of these emissions are related to bubble size distribution and emission flux, providing important information on methane release from the seafloor. Long-term passive acoustic monitoring was used to continuously record seep sounds over a 7-month period within the blowout crater at the abandoned well site, 22/4b, in the central North Sea. Also recorded were water column fluid velocities and near-seafloor water conductivity, temperature, and pressure. Acoustic signatures were primarily from ∼1 to 10 kHz. Key features were relatively broad spectral peaks at about 1.0, 1.5, 2.2, 3.1, 3.6 and 5.1 kHz. Temporal variations in spectral levels were apparently associated with tides. The recordings also documented a series of major episodic events including a large and persistent increase (∼10 dB) in overall sound levels and spectral broadening on 8 December 2011. The acoustic temporal pattern of this event was consistent with other recorded large transient events in the literature, and the major event was correlated with dramatic changes in other measurements, including increased water column fluid velocities, increased pressure and decreased salinity, indicating real changes in emission flux. Observed seabed morphology changes reported elsewhere in this special issue, also likely were related to this event. These data demonstrate the dynamic nature of marine seepage systems, show the value of monitoring systems, and provide direct supporting evidence for a violent formation mechanism of many widespread seep-associated seabed features like pockmarks.

Wiggins, SM, Hildebrand JA, Gieskes JM.  2002.  Geothermal state and fluid flow within ODP Hole 843B: results from wireline logging. Earth and Planetary Science Letters. 195:239-248.   10.1016/s0012-821x(01)00590-8   AbstractWebsite

Borehole fluid temperatures were measured with a wireline re-entry system in Ocean Drilling Program Hole 843B, the site of the Ocean Seismic Network Pilot Experiment. These temperature data, recorded more than 7 years after drilling, are compared to temperature data logged during Leg 136, approximately I day after drilling had ceased. Qualitative interpretations of the temperature data suggest that fluid flowed slowly downward in the borehole immediately following drilling, and flowed slowly upward 7 years after drilling. Quantitative analysis suggests that the upward fluid flow rate in the borehole is approximately 1 m/h. Slow fluid flow interpreted from temperature data only, however, requires estimates of other unmeasured physical properties. If fluid flows upward in Hole 843B, it may have led to undesirable noise for the borehole seismometer emplaced in this hole as part of the Ocean Seismic Network Pilot Experiment, Estimates of conductive heat flow from ODP Hole 843B are 51 mW/m(2) for the sediment and the basalt. These values are lower than the most recent Hawaiian Arch seafloor heat flow studies. (C) 2002 Elsevier Science B.V. All rights reserved.

Wiggins, SM, Oleson EM, McDonald MA, Hildebrand JA.  2005.  Blue whale (Balaenoptera musculus) diel call patterns offshore of southern California. Aquatic Mammals. 31:161-168.   10.1578/AM.31.2.2005.161   AbstractWebsite

Diel and seasonal calling patterns for blue whales (Balaenoptera musculus) were observed in coastal waters off southern California using seafloor-mounted autonomous acoustic recording packages (ARPs). Automated call counting from spectrogram cross-correlation showed peak seasonal calling in late summer/early fall. When call counts were organized by daily time intervals, calling peaks were observed during twilight periods, just after sunset and before sunrise. Minimum calling was observed during the day. Nighttime calling was greater than daytime calling, but also showed a minimum between the dusk and dawn calling peaks. These peaks correlate with the vertical migration times of krill, the blue whales' primary prey. One hypothesis to explain these diel variations is that blue whale calling and foraging may be mutually exclusive activities. Fewer calls are produced during the day while prey are aggregated at depth and foraging is efficient. More calls are produced during the twilight time periods when prey are vertically migrating and at night when prey are dispersed near the sea surface and foraging is less efficient.

Wiggins, SM, Hall JM, Thayre BJ, Hildebrand JA.  2016.  Gulf of Mexico low-frequency ocean soundscape impacted by airguns. Journal of the Acoustical Society of America. 140:176-183.   10.1121/1.4955300   AbstractWebsite

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 mu Pa-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 mu Pa-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. (C) 2016 Author(s).

Wiggins, SM, Dorman LM, Cornuelle BD.  1997.  Topography can affect linearization in tomographic inversions. Geophysics. 62:1797-1803.   10.1190/1.1444280   AbstractWebsite

Linearized inverse techniques commonly are used to solve for velocity models from traveltime data. The amount that a model may change without producing large, nonlinear changes in the predicted traveltime data is dependent on the surface topography and parameterization. Simple, one-layer, laterally homogeneous, constant-gradient models are used to study analytically and empirically the effect of topography and parameterization on the linearity of the model-data relationship. If, in a weak-velocity-gradient model, rays turn beneath a valley with topography similar to the radius of curvature of the raypaths, then large nonlinearities will result from small model perturbations. Hills, conversely, create environments in which the data are more nearly linearly related to models with the same model perturbations.

Wiggins, SM, McDonald MA, Munger LM, Moore SE, Hildebrand JA.  2004.  Waveguide propagation allows range estimates for North Pacific right whales in the Bering Sea. Canadian Acoustics. 32:146-154. AbstractWebsite

The shallow and uniform water depth of the eastern Bering Sea shelf results in an acoustic waveguide. Propagation within this waveguide produces waveform dispersion which is dependent upon range. We present a means for using dispersed waveforms to determine range to calling whales from a single autonomous acoustic recording instrument. The predominant North Pacific right whale (Evbalaena japonica) call is frequency upswept from about 90 Hz to around 160 Hz and lasts approximately 1 s. The regional bathymetry of the eastern Bering Sea middle shelf is relatively uniform and shallow ( similar to 70 meters deep). This geometry provides a plane-layered waveguide in which right whale upswept calls can be detected at ranges over 50 km and have multiple modal arrivals that become dispersed, displaying different propagation velocities for different frequencies. Dispersion characteristics of modal arrivals are dependent on the calling whale's depth, the receiver's depth, the water depth, the range from caller to receiver, and various environmental parameters including water and sediment density and sound velocity. A model of sound propagation for the eastern Bering Sea middle shelf is developed from right whale call dispersion recorded on sonobuoys and seafloor acoustic recording packages, using individual calls recorded at multiple instruments. After development of the model, waveform dispersion allows estimation of caller range based on single instrument recordings. Estimating range between instrument and calling whales provides a means to estimate minimum abundance for the endangered North Pacific right whale.Original Abstract: L'eau peu profonde et uniforme de la rive Est de la mer de Bering produit un excellent guide d'ondes acoustiques. Dans ce guide de propagation, la dispersion des ondes sonores est dependante de la distance. Nous presentons ici un moyen pour utiliser la dispersion des ondes sonores pour determiner la portee de sons emis par des baleines a partir d'un unique instrument d'enregistrement du signal acoustique. La vocalisation predominate de la baleine franche du Pacifique Nord (Eubalaena japonica) est une modulation ascendante d'environ 90 a 160 Hz et d'une duree approximative de 1 s. La bathymetrie regionale de la rive Est de la mer de Bering est relativement uniforme et peu profonde ( similar to 70 m de profondeur). Cette geometrie fournit un guide d'ondes a couches horizontales ou les vocalisations modulees de baleines tranches peuvent etre detectees a des distances superieures a 50 km et ont de multiples arrivees modales qui deviennent dispersees, demontrant differente vitesse de propagation a differentes frequences. Les caracteristiques de dispersion des arrivees modales sont dependantes de la profondeur de la baleine, la profondeur du recepteur, la profondeur de l'eau. la distance de l'emetteur et du recepteur et une variete de parametres environnementaux incluant la densite de l'eau et des sediments, et la vitesse du son dans ces deux media. Un modele de la propagation du son pour la rive Est de la mer de Bering est developpe a partir de la dispersion des vocalisations des baleines tranches enregistrees a partir de bouees acoustiques et de systemes acoustiques ancres sur le fond marin, en utilisant les vocalisations individuelles enregistrees a partir de multiples instruments. Apres le developpement du modele, la dispersion de l'onde sonore permet l'estimation de la distance de la vocalisation basee sur l'enregistrement d'un seul instrument. Estimer la distance entre l'instrument et les vocalisations de baleines permet d'estimer l'abondance minimale de la baleine franche menacee d'extinction dans le Pacitique Nord.

Wiggins, SM, Hildebrand JA.  2016.  Long-Term Monitoring of Cetaceans Using Autonomous Acoustic Recording Packages. Listening in the Ocean. ( Au WWL, Lammers MO, Eds.).:35-59.: Springer New York   10.1007/978-1-4939-3176-7_3   Abstract

Autonomous acoustic recorders have advanced our understanding of cetaceans, providing information for better models of species distribution, behavior, ecology, and conservation. For over a decade, Acoustic Recording Packages (ARPs), and its broader-bandwidth successor, High-frequency Acoustic Recording Package (HARP), have been used for Passive Acoustic Monitoring (PAM) providing high-fidelity, long-term acoustic data sets for cetacean studies. Some of these studies are summarized below showing a wide range of applications and results including species signal characterization, seasonal and daily presence patterns, geographic and habitat use, population density and abundance estimations, acoustic stimuli behavioral response, and swimming behavior via array tracking. Species studied include low-frequency baleen whales and high-frequency dolphins and beaked whales.

Wiggins, SM, Frasier KE, Henderson EE, Hildebrand JA.  2013.  Tracking dolphin whistles using an autonomous acoustic recorder array. The Journal of the Acoustical Society of America. 133:3813-3818.: ASA   http://dx.doi.org/10.1121/1.4802645   AbstractWebsite

Dolphins are known to produce nearly omnidirectional whistles that can propagate several kilometers, allowing these sounds to be localized and tracked using acoustic arrays. During the fall of 2007, a km-scale array of four autonomous acoustic recorders was deployed offshore of southern California in a known dolphin habitat at ∼800 m depth. Concurrently with the one-month recording, a fixed-point marine mammal visual survey was conducted from a moored research platform in the center of the array, providing daytime species and behavior visual confirmation. The recordings showed three main types of dolphin acoustic activity during distinct times: primarily whistling during daytime, whistling and clicking during early night, and primarily clicking during late night. Tracks from periods of daytime whistling typically were tightly grouped and traveled at a moderate rate. In one example with visual observations, traveling common dolphins (Delphinus sp.) were tracked for about 10 km with an average speed of ∼2.5 m s−1 (9 km h−1). Early night recordings had whistle localizations with wider spatial distribution and slower travel speed than daytime recordings, presumably associated with foraging behavior. Localization and tracking of dolphins over long periods has the potential to provide insight into their ecology, behavior, and potential response to stimuli.

Wiggins, SM, Dorman LRM, Cornuelle BD, Hildebrand JA.  1996.  Hess Deep rift valley structure from seismic tomography. Journal of Geophysical Research-Solid Earth. 101:22335-22353.   10.1029/96jb01230   AbstractWebsite

We present results from a seismic refraction experiment conducted across the Hess Deep rift valley in the equatorial east Pacific. P wave travel times between seafloor explosions and ocean bottom seismographs are analyzed using an iterative stochastic inverse method to produce a velocity model of the subsurface structure. The resulting velocity model differs from typical young, fast spreading, East Pacific Rise crust by approximately +/-1 km/s with slow velocities beneath the valley of the deep and a fast region forming the intrarift ridge. We interpret these velocity contrasts as lithologies originating at different depths and/or alteration of the preexisting rock units. We use our seismic model, along with petrologic and bathymetric data from previous studies, to produce a structural model. The model supports low-angle detachment faulting with serpentinization of peridotite as the preferred mechanism for creating the distribution and exposure of lower crustal and upper mantle rocks within Hess Deep.

Wiggins, S.  2003.  Autonomous acoustic recording packages (ARPs) for long-term monitoring of whale sounds. Marine Technology Society Journal. 37:13-22.   10.4031/002533203787537375 pp.13-22   AbstractWebsite

Advancements in low-power and high-data capacity computer technology during the past decade have been adapted to autonomously record acoustic data from vocalizing whales over long time periods. Acoustic monitoring of whales has advantages over traditional visual surveys including greater detection ranges, continuous long-term monitoring in remote locations and in various weather conditions, and lower cost. An autonomous acoustic recording package (ARP) is described that uses a tethered hydrophone above a seafloor-mounted instrument frame. ARPs have been deployed to record baleen whale sounds in the Bering Sea, off the coast of southern California, near the West Antarctic Peninsula, and near Hawaii. ARP data have provided new information on the seasonal presence, abundance, call character, and patterns of vocalizing whales. Current development is underway for a broader-band, higher-data capacity system capable of recording odontocete whales, dolphins, and porpoises for long time periods.

Wiggins, SM, McDonald MA, Hildebrand JA.  2012.  Beaked whale and dolphin tracking using a multichannel autonomous acoustic recorder. The Journal of the Acoustical Society of America. 131:156-163.   10.1121/1.3662076   AbstractWebsite

To track highly directional echolocation clicks from odontocetes, passive hydrophone arrays with small apertures can be used to receive the same high frequency click on each sensor. A four-hydrophone small-aperture array was coupled to an autonomous acoustic recorder and used for long-term tracking of high-frequency odontocete sounds. The instrument was deployed in the spring of 2009 offshore of southern California in a known beaked whale and dolphin habitat at about 1000 m depth. The array was configured as a tetrahedron with approximately 0.5 m sensor spacing. Time difference of arrival measurements between the six sensor-pairs were used to estimate three-dimensional bearings to sources. Both near-seafloor beaked whales and near-sea surface dolphins were tracked. The tracks observed using this technique provide swimming and diving behavioral information for free-ranging animals using a single instrument. Furthermore, animal detection ranges were derived, allowing for estimation of detection probability functions. (C) 2012 Acoustical Society of America. [DOI: 10.1121/1.3662076]