Recent Publications

Weekly Highlighted Publication

Eddy properties in the Southern California Current System

Impact:
This study has focused on mesoscale activity in the Southern CCS using a 5-km horizontal resolution model. Using an eddy detection and tracking algorithm based on the Okubo-Weiss parameter, we found that mesoscale activity in the SCCS was dominated by cyclonic eddies, consistent with in situ data (Stegmann and Schwing 2007). On average, these eddies have a diameter of 50 km and can remain distinct for up to 190 days. The vertical structure of the average cyclonic eddy obtained from averaging ~ 4000 eddies shows a consistent doming of isopycnals in the eddy center, bringing deep, cold, salty, and nutrient-rich water closer to the surface. These cyclonic eddies are formed at the coast through current instabilities, mostly in the fall. Eddies consistently trapped water from the northward-flowing California Undercurrent and the southward-flowing shallow California Current, and transported these water masses offshore at a speed of ~ 2 km day−1.

Search Recent Publications

  • Abstract Summary:

    The magnitude and spectral shape of the optical backscattering coefficient of particles, b(bp)(lambda), is being increasingly used to infer information about the particles present in seawater. Relationships between b(bp) and particle properties in the Arctic are poorly documented, and may differ from other oceanic regions which contribute the majority of data used to develop and parameterize optical models. We utilize recent field...

  • Abstract Summary:

    A deep-water experiment in the Pacific made in situ measurements of the volume attenuation coefficients of sea water in the mid-frequency range. The frequency, temperature, salinity, pH, and pressure dependent seawater attenuation coefficients were determined using a vertical line array that received and identified over 2000 unique paths from 1200 mid-frequency 3-9 kHz LFM source transmissions at a convergence zone range and depth up to 400 m...

  • Abstract Summary:

    The deployment and recovery of autonomous or remotely piloted platforms from research vessels have become a way of significantly extending the capabilities and reach of the research fleet. This paper describes the use of ship-launched and ship-recovered Boeing-Insitu ScanEagle unmanned aerial vehicles (UAVs). The UAVs were instrumented to characterize the marine atmospheric boundary layer (MABL) structure and dynamics, and to measure ocean...

  • Abstract Summary:

    We examine the geometry, kinematics, and dynamics of weakly nonlinear narrow-banded deep-water wave packets governed by the modified nonlinear Schrodinger equation (Dysthe, Proc. R. Soc. Load. A., vol. 369, 1979, pp. 105-114; MNLSE). A new derivation of the spatial MNLSE, by a direct application of Whitham's method, elucidates its variational structure. Using this formalism, we derive a set of conserved quantities and moment evolution...

  • Deike L., Melville W.K, Popinet S..  2016.  Air entrainment and bubble statistics in breaking waves. Journal of Fluid Mechanics. 801:91-129.
    Abstract Summary:

    We investigate air entrainment and bubble statistics in three-dimensional breaking waves through novel direct numerical simulations of the two-phase air-water flow, resolving the length scales relevant for the bubble formation problem, the capillary length and the Hinze scale. The dissipation due to breaking is found to be in good agreement with previous experimental observations and inertial scaling arguments. The air entrainment properties...

  • Abstract Summary:

    Bioinspired ZrO2-epoxy, two-phase composite materials were fabricated by the freeze casting fabrication technique followed by polymer infiltration. These materials were intrinsically controlled by adding varying concentrations of the monofunctional alcohols ethanol (EtOH), n-propanol (n-PrOH) and n-butanol (n-BuOH). The microstructures of freeze cast scaffolds created with these alcohol additives demonstrated maximum pore areas (peak A(p)) at...

  • Walstead SP, Deane GB.  2016.  Determination of ocean surface wave shape from forward scattered sound. Journal of the Acoustical Society of America. 140:787-797.
    Abstract Summary:

    Forward scattered sound from the ocean surface is inverted for wave shape during three periods: low wind, mix of wind and swell, and stormy. Derived wave profiles are spatially limited to a Fresnel region at or near the nominal surface specular reflection point. In some cases, the surface wave profiles exhibit unrealistic temporal and spatial properties. To remedy this, the spatial gradient of inverted waves is constrained to a maximum slope...

  • Abstract Summary:

    The pH on the total proton scale of the Tris-HCl buffer system (pH(Tris)) was characterized rigorously with the electrochemical Flamed cell in salinity (S) 35 synthetic seawater and S = 45-100 synthetic seawater-derived brines at 25 and 0 degrees C, as well as at the freezing point of the synthetic solutions (-1.93 degrees C at S = 35 to -6 degrees C at S = 100). The electrochemical characterization of the common equimolal Tris buffer [R-Tris...

  • Abstract Summary:

    The abyssal flow of water through the Samoan Passage accounts for the majority of the bottom water renewal in the North Pacific, thereby making it an important element of the meridional overturning circulation. Here the authors report recent measurements of the flow of dense waters of Antarctic and North Atlantic origin through the Samoan Passage. A 15-month long moored time series of velocity and temperature of the abyssal flow was recorded...

  • Abstract Summary:

    Actinomycete bacteria of the common genus Streptomyces can be routinely isolated from shallow and deep ocean sediments. Although commonly considered a terrestrial genus, and most abundantly found in soil, Streptomyces strains are found that have distinct requirements for seawater and routinely do not show significant similarity, with terrestrial strains by 16S ribosomal DNA phylogenetic sequence comparisons. Our examination of the culture...

  • Highlighted Publication
    Guass O., Haapanen L.M, Dowd S.E, Sirovic A., McLaughlin R.W.  2016.  Analysis of the microbial diversity in faecal material of the endangered blue whale, Balaenoptera musculus. Antonie Van Leeuwenhoek International Journal of General and Molecular Microbiology. 109:1063-1069.
    Abstract Summary:

    Using bacterial and fungal tag-encoded FLX-Titanium amplicon pyrosequencing, the microbiota of the faecal material of two blue whales living in the wild off the coast of California was investigated. In both samples the most predominant bacterial phylum was the Firmicutes with Clostridium spp. being the most dominant bacteria. The most predominant fungi were members of the phylum Ascomycota with Metschnikowia spp. being the most dominant. In...

  • Abstract Summary:

    Tonal vocalizations or whistles produced by many species of delphinids range from simple tones to complex frequency contours. Whistle structure varies in duration, frequency, and composition between delphinid species, as well as between populations and individuals. Categorization of whistles may be improved by decomposition of complex calls into simpler subunits, much like the use of phonemes in classification of human speech. We identify a...

  • Wiggins SM, Hall J.M, Thayre B.J, Hildebrand JA.  2016.  Gulf of Mexico low-frequency ocean soundscape impacted by airguns. Journal of the Acoustical Society of America. 140:176-183.
    Abstract Summary:

    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...

  • Abstract Summary:

    We develop an optical classification of marine particle assemblages from an extensive dataset of particle optical properties collected in the Chukchi and Beaufort Seas. Hierarchical cluster analysis of the spectral particulate backscattering-to-absorption ratio partitioned the dataset into seven optically-distinct clusters of particle assemblages, each associated with different characteristics of particle concentration, composition, and...

  • Song HC.  2016.  An overview of underwater time-reversal communication. Ieee Journal of Oceanic Engineering. 41:644-655.
    Abstract Summary:

    Time reversal (TR) exploits spatial diversity to achieve spatial and temporal focusing in complex environments. Over the last decade, the TR concept has been applied successfully to phase-coherent acoustic communications in time-varying multipath ocean environments, as an alternative to conventional adaptive multichannel equalization. Temporal focusing ( pulse compression) mitigates the intersymbol interference (ISI) and subsequent single-...

  • Michalopoulou Z.H, Gerstoft P.  2016.  Passive fathometer reflector identification with phase shift modeling. Journal of the Acoustical Society of America. 140:EL125-EL130.
    Abstract Summary:

    In passive fathometer processing, the presence of wavelets in the estimate of the medium's Green's function corresponds to the location of reflectors in the seabed; amplitudes are related to seabed properties. Bayesian methods have been successful in identifying reflectors that define layer interfaces. Further work, however, revealed that phase shifts are occasionally present in the wavelets and hinder accurate layer identification for some...

  • Highlighted Publication Regional bathymetry of the CNTL15RR cruise
    DeSanto J.B, Sandwell DT, Chadwell C.D.  2016.  Seafloor geodesy from repeated sidescan sonar surveys. Journal of Geophysical Research-Solid Earth. 121:4800-4813.
    Abstract Summary:

    Accurate seafloor geodetic methods are critical to the study of marine natural hazards such as megathrust earthquakes, landslides, and volcanoes. We propose digital image correlation of repeated shipboard sidescan sonar surveys as a measurement of seafloor deformation. We test this method using multibeam surveys collected in two locales: 2500m deep lightly sedimented seafloor on the flank of a spreading ridge and 4300m deep heavily sedimented...

  • Abstract Summary:

    The Antarctic minke whale (Balaenoptera bonaerensis) is a difficult species to study because of its low visual detectability and preference for living within the sea ice habitat, accessible only by ice-strengthened vessels. Recent identification of the Antarctic minke whale as the source of the seasonally ubiquitous bio-duck call has allowed the use of this sound, as well as downsweeps, to investigate seasonality trends and diel patterns in...

  • Abstract Summary:

    Sunlight induced chlorophyll a fluorescence (SICF) can be used as a probe to estimate chlorophyll a concentrations (Chl) and infer phytoplankton physiology. SICF at approximate to 685 nm has been widely applied to studies of natural waters. SICF around 740 nm has been demonstrated to cause a narrow reflectance peak at approximate to 761 nm in the reflectance spectra of terrestrial vegetation. This narrow peak has also been observed in the...

  • Abstract Summary:

    Microscopic-scale processes significantly influence benthic marine ecosystems such as coral reefs and kelp forests. Due to the ocean/'s complex and dynamic nature, it is most informative to study these processes in the natural environment yet it is inherently difficult. Here we present a system capable of non-invasively imaging seafloor environments and organisms in situ at nearly micrometre resolution. We overcome the challenges of...

  • Abstract Summary:

    This study investigated the effects of using duty-cycled passive acoustic recordings to monitor the daily presence of beaked whale species at three locations in the northwest Atlantic. Continuous acoustic records were subsampled to simulate duty cycles of 50%, 25%, and 10% and cycle period durations from 10 to 60 min. Short, frequent listening periods were most effective for assessing the daily presence of beaked whales. Furthermore,...

  • Melville W.K, Lenain L., Cayan DR, Kahru M, Kleissl J.P, Linden P.F, Statom N.M.  2016.  The Modular Aerial Sensing System. Journal of Atmospheric and Oceanic Technology. 33:1169-1184.
    Abstract Summary:

    Satellite remote sensing has enabled remarkable progress in the ocean, earth, atmospheric, and environmental sciences through its ability to provide global coverage with ever-increasing spatial resolution. While exceptions exist for geostationary ocean color satellites, the temporal coverage of low-Earth-orbiting satellites is not optimal for oceanographic processes that evolve over time scales of hours to days. In hydrology, time scales can...

  • Abstract Summary:

    As a part of the US Air-Sea Interactions Regional Initiative, the first extensive set of turbulent kinetic energy dissipation rate (epsilon) measurements from microstructure profilers were obtained in the Bay of Bengal (BoB) and around Sri Lanka during 2013-2015. The observations span almost 1,200 km meridionally, and capture the dynamics associated with a variety of mesoscale and submesoscale features. High freshwater input in the northern...

  • Abstract Summary:

    Upper-ocean turbulent heat fluxes in the Bay of Bengal and the Arctic Ocean drive regional monsoons and sea ice melt, respectively, important issues of societal interest. In both cases, accurate prediction of these heat transports depends on proper representation of the small-scale structure of vertical stratification, which in turn is created by a host of complex submesoscale processes. Though half a world apart and having dramatically...

  • Abstract Summary:

    The aeolid nudibranch Fiona pinnata (Eschscholtz, 1831) is an obligate rafter that occurs exclusively on macroalgal rafts and other floating substrata, and has a seemingly cosmopolitan marine distribution. Mitochondrial (mtDNA) and nuclear DNA sequence data were generated from specimens collected worldwide to test for global connectivity in this species. Phylogeographic analyses revealed three divergent mtDNA lineages, two of which were...

  • Zhao Z, Alford MH, Girton JB, Rainville L, Simmons HL.  2016.  Global observations of open-ocean mode-1 M2 internal tides. Journal of Physical Oceanography. 46:1657-1684.
    Abstract Summary:

    AbstractA global map of open-ocean mode-1 M2 internal tides is constructed using sea surface height (SSH) measurements from multiple satellite altimeters during 1992–2012, representing a 20-yr coherent internal tide field. A two-dimensional plane wave fit method is employed to 1) suppress mesoscale contamination by extracting internal tides with both spatial and temporal coherence and 2) separately resolve multiple internal tidal waves....

  • Abstract Summary:

    An L-configured, three-component short period seismic array was deployed on the Ross Ice Shelf, Antarctica during November 2014. Polarization analysis of ambient noise data from these stations shows linearly polarized waves for frequency bands between 0.2 and 2 Hz. A spectral peak at about 1.6 Hz is interpreted as the resonance frequency of the water column and is used to estimate the water layer thickness below the ice shelf. The frequency...

  • Walstead SP, Deane GB.  2016.  Intensity statistics of very high frequency sound scattered from wind-driven waves. Journal of the Acoustical Society of America. 139:2784-2796.
    Abstract Summary:

    The interaction of vhf 100-1000 kHz underwater sound with the ocean surface is explored. The bistatic forward scatter of 300 kHz sound is measured in a wind driven wave channel. Fluctuations in arrival amplitude are described by the scintillation index (SI) which is a measure of arrival intensity variance. SI initially increases with wind speed but eventually saturates to a value of 0.5 when the root-mean-square (rms) roughness is 0.5 mm. An...

  • Chen Z., Gerstoft P, Bromirski PD.  2016.  Microseism source direction from noise cross-correlation. Geophysical Journal International. 205:810-818.
    Abstract Summary:

    Inhomogeneous noise sources surrounding stations produce asymmetric amplitudes in cross-correlation functions that yield preferential source directions. Here we show that preprocessing biases the dominant source direction estimate towards the source producing long-duration signals by down-weighting high-amplitude signals. Tests with both synthetic data and observations show that conventional preprocessing, where only earthquakes and local...

  • Sirovic A., Hildebrand JA, McDonald M.A.  2016.  Ocean ambient sound south of Bermuda and Panama Canal traffic. Journal of the Acoustical Society of America. 139:2417-2423.
    Abstract Summary:

    Comparisons of current and historic ocean ambient noise levels are rare, especially in the North Atlantic. Recent (2013-2014) monthly patterns in ocean ambient sound south of Bermuda were compared to those recorded at the same location in 1966. Additionally, trends in ocean traffic, in particular, Panama Canal traffic, over this time were also investigated. One year of ocean ambient noise measurements were collected in 1966 using cabled,...

  • DeMott PJ, Hill T.CJ, McCluskey C.S, Prather KA, Collins DB, Sullivan RC, Ruppel MJ, Mason R.H, Irish V.E, Lee T. et al..  2016.  Sea spray aerosol as a unique source of ice nucleating particles. Proceedings of the National Academy of Sciences of the United States of America. 113:5797-5803.
    Abstract Summary:

    Ice nucleating particles (INPs) are vital for ice initiation in, and precipitation from, mixed-phase clouds. A source of INPs from oceans within sea spray aerosol (SSA) emissions has been suggested in previous studies but remained unconfirmed. Here, we show that INPs are emitted using real wave breaking in a laboratory flume to produce SSA. The number concentrations of INPs from laboratory-generated SSA, when normalized to typical total...

  • Sirovic A..  2016.  Variability in the performance of the spectrogram correlation detector for North-east Pacific blue whale calls. Bioacoustics-the International Journal of Animal Sound and Its Recording. 25:145-160.
    Abstract Summary:

    Spectrogram correlation has been used successfully for automatic detection of baleen whale calls. However, applying this method consistently to long time series can be challenging. To illustrate the potential challenges of the automatic detection process, recordings collected in the Southern California Bight between 2007 and 2012 were used for detection of North-east Pacific blue whale (Balaenoptera musculus) B calls. The effects of the...

  • Abstract Summary:

    Masking from industrial noise can hamper the ability to detect marine mammal sounds near industrial operations, whenever conventional (pressure sensor) hydrophones are used for passive acoustic monitoring. Using data collected from an autonomous recorder with directional capabilities (Directional Autonomous Seafloor Acoustic Recorder), deployed 4.1 km from an arctic drilling site in 2012, the authors demonstrate how conventional beamforming...

  • Abstract Summary:

    In propagating wave systems, three- or four-wave resonant interactions constitute a classical nonlinear mechanism exchanging energy between the different scales. Here we investigate three-wave interactions for gravity-capillary surface waves in a closed laboratory tank. We generate two crossing wave trains and we study their interaction. Using two optical methods, a local one (laser doppler vibrometry) and a spatiotemporal one (diffusive...

  • Abstract Summary:

    In situ observations of tidally driven turbulence were obtained in a small channel that transects the crest of the Mendocino Ridge, a site of mixed (diurnal and semidiurnal) tides. Diurnal tides are subinertial at this latitude, and once per day a trapped tide leads to large flows through the channel giving rise to tidal excursion lengths comparable to the width of the ridge crest. During these times, energetic turbulence is observed in the...

  • Bianco M, Gerstoft P.  2016.  Compressive acoustic sound speed profile estimation. The Journal of the Acoustical Society of America. 139:EL90-EL94.
    Abstract Summary:

    Ocean acoustic  sound speed   profile (SSP) estimation requires the inversion of acoustic fields using limited observations. Compressive sensing (CS) asserts that certain underdetermined problems can be solved in high resolution, provided their solutions are sparse. Here, CS is used to estimate SSPs in a range-independent shallow ocean by inverting a non-linear acoustic propagation model. It is shown that SSPs can be estimated using CS to...

  • Abstract Summary:

    Microbial viruses can control host abundances via density-dependent lytic predator-prey dynamics. Less clear is how temperate viruses, which coexist and replicate with their host, influence microbial communities. Here we show that virus-like particles are relatively less abundant at high host densities. This suggests suppressed lysis where established models predict lytic dynamics are favoured. Meta-analysis of published viral and microbial...

  • Scanlon B., Breivik O., Bidlot J.R, Janssen P, Callaghan AH, Ward B..  2016.  Modeling whitecap fraction with a wave model. Journal of Physical Oceanography. 46:887-894.
    Abstract Summary:

    High-resolution measurements of actively breaking whitecap fraction (W-FA) and total whitecap fraction (W-FT) from the Knorr11 field experiment in the Atlantic Ocean are compared with estimates of whitecap fraction modeled from the dissipation source term of the ECMWF wave model. The results reveal a strong linear relationship between model results and observed measurements. This indicates that the wave model dissipation is an accurate...

  • Highlighted Publication
    Abstract Summary:

    Measurements of energy dissipated in breaking laboratory waves, averaged over time and space and directly visualized with a bioluminescent technique, are presented. These data show that the energy dissipated in the crest of the breaking waves is constrained: average turbulence intensity within the crest saturates at around 0.5-1.2 W kg(-1), whereas breaking crest volume scales with wave energy lost. These results are consistent with...

  • Abstract Summary:

    High-spatial-resolution, near-surface vertical profiling of atmospheric chemical composition is currently limited by the availability of experimental platforms that can sample in constrained environments. As a result, measurements of near surface gradients in trace gas and aerosol particle concentrations have been limited to studies conducted from fixed location towers or tethered balloons. Here, we explore the utility of a quadrotor unmanned...

  • 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.
    Abstract Summary:

    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...

  • Sabra KG, Cornuelle B., Kuperman WA.  2016.  Sensing deep-ocean temperatures. Physics Today. 69:32-38.
    Abstract Summary:

    Though not yet widely implemented, the technique of monitoring the ocean's warming via changes in the speed of sound through the water is a powerful complement to the more common tools available: free-floating thermometers and altimetry satellites.


  • Abstract Summary:

    Recent expansion in the capabilities of passive acoustic monitoring of sound-producing animals is providing expansive data sets in many locations. These long-term data sets will allow the investigation of questions related to the ecology of sound-producing animals on time scales ranging from diel and seasonal to inter-annual and decadal. Analyses of these data often span multiple analysts from various research groups over several years of...

  • Abstract Summary:

    Models of the air-sea transfer velocity of gases may be either empirical or mechanistic. Extrapolations of empirical models to an unmeasured gas or to another water temperature can be erroneous if the basis of that extrapolation is flawed. This issue is readily demonstrated for the most well-known empirical gas transfer velocity models where the influence of bubble-mediated transfer, which can vary between gases, is not explicitly accounted...

  • Abstract Summary:

    Brachiopods have been widely used as proxies to reconstruct ancient oceanographic conditions based on the assumption that their shell calcite is precipitated in near isotopic equilibrium with ambient seawater. Few studies, however, have tested the presumption of equilibrium precipitation for specimens from extreme polar environments. Furthermore, reported isotopic values for polar specimens are largely indicative of disequilibrium...

  • Abstract Summary:

    This study assesses the ability of hyperspectral optical measurements to discriminate changes in the composition of phytoplankton communities in open-ocean non-bloom environments. A large set of in situ near-surface measurements, comprising phytoplankton pigment determinations and hyperspectral optical data of phytoplankton absorption coefficient, aph(λ), and remote-sensing reflectance, Rrs(λ), are used in the analysis. Measurements were...

  • Abstract Summary:

    Matched field processing(MFP) is an established technique for source localization in known multipath acoustic environments. Unfortunately, in many situations, particularly those involving high frequency signals, imperfect knowledge of the actual propagation environment prevents accurate propagation modeling and source localization via MFP fails. For beamforming applications, this actual-to-model mismatch problem was mitigated through a...

  • Alford MH, McGinnis T., Howe B.M.  2015.  An inductive charging and real-time communications system for profiling moorings. Journal of Atmospheric and Oceanic Technology. 32:2243-2252.
    Abstract Summary:

    This paper describes a system for providing power and communications to moored profiling vehicles. A McLane Moored Profiler (MP) was equipped with a rechargeable battery pack and an inductive charging system to allow it to move periodically to a charging dock at the top of a subsurface mooring. Power was provided from a large bank of alkaline batteries housed in two 0.94-m steel spheres. Data were transferred inductively from the profiler to...

  • Smith JA.  2015.  Revisiting oceanic acoustic gravity surface waves. Journal of Physical Oceanography. 45:2953-2958.
    Abstract Summary:

    AbstractThe reintroduction of compressibility into the equations for surface gravity waves can permit mixed acoustic?gravity modes that are periodic in the vertical as well as horizontal directions. These modes interact with the bottom even in deep water, so bottom motion can excite them. Because they propagate rapidly, it has been suggested they may be useful as precursors of tsunamis. Here the equations are revisited, and, using some robust...

  • Abstract Summary:

    Cuttlefish are cephalopods capable of rapid camouflage responses to visual stimuli. However, it is not always clear to what these animals are responding. Previous studies have found cuttlefish to be more responsive to lateral stimuli rather than substrate. However, in previous works, the cuttlefish were allowed to settle next to the lateral stimuli. In this study, we examine whether juvenile cuttlefish (Sepia officinalis) respond more...

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