@article {7221, title = {Buoyancy-Modified Entrainment in Plumes: Theoretical Predictions}, volume = {34(1)}, year = {2022}, month = {January 12}, abstract = {

A theoretical analysis, based on the self-similar velocity and buoyancy profiles for plumes in the far field region, is conducted to show how buoyancy dually shapes the flow behavior. In particular, it is shown that while buoyancy flux makes a positive contribution to the mean kinetic energy flux, buoyancy also enhances the momentum flux, through which the mean shear is enhanced. This amplifies the loss of mean kinetic energy into turbulent kinetic energy. The ability of buoyancy to increase the range of flow length scales is discussed in terms of its impact on the evolutionary dynamics of the flow structures. It is also shown, as a result of the scaling laws that follow from the analysis, that the ability of buoyancy to strengthen the eddy vorticity in plumes is primarily through its leading order effect of enhancing the mean flow, and hence the mean shear, and less so through its lower order contributions to the baroclinic component of torque. We then provide a perspective on how the small-scale nibbling contribution to the entrainment process is affected by such buoyancy-induced modifications to the mean flow. Finally, key takeaways from the analysis are juxtaposed with the modern-day view provided by the literature on the entrainment process to propose a mechanistic picture of buoyancy-modified entrainment in plumes.

}, doi = {10.1063/5.0065265}, author = {Zeeshan Saeed and Elizabeth Weidner and Blair A Johnson and Tracy L Mandel} } @mastersthesis {7378, title = {The Layer That Didn{\textquoteright}t Swim Away: Broadband Acoustic Characterization of Oceanic Stratification Structure}, volume = {Oceanography}, year = {2022}, month = {September 2022}, school = {University of New Hampshire}, address = {Durham, NH}, abstract = {

Ocean stratification structure plays a critical role in many oceanographic processes. The magnitude of mixing between stable water masses is regulated, in part, by the intensity of stratification. As such, stratification structure modulates the vertical transport of heat and many important dissolved constituents in the water column, influencing such processes as ocean ventilation, and ocean heat and carbon uptake. As human induced climate change alters oceanic stratification structure a thorough understanding of its the distribution and variability is critical in the study of the world\’s oceans. However, traditional methods are limited in terms of spatial context and rapid, synoptic observational methods, such as those provided by active acoustic systems, are needed to fill in the gaps.

Broadband acoustic water column data have already been used to observe ocean structure and commercial systems are becoming increasingly available. However, broadband acoustic methods for characterizing oceanic stratification structure are not well developed, limiting of applicability of broadband data to the study, quantification, and monitor ocean stratification structure as the world warms. This thesis aims to develop quantitative acoustic methods for characterization of ocean stratification structure using active broadband acoustic systems.

This work leveraged the high range resolution and signal to noise ratios, as well as the frequency-modulated scattering response of broadband acoustic systems. Broadband acoustic methods were developed and established through 1) the analysis of field data from different ocean basins and 2) the development and application of acoustic scattering models. This work will provide the means to better understand the physical mechanisms responsible for acoustic backscattering from stratification structure, working towards rapid, remote, high-resolution measurements of ocean stratification structure through acoustic inversion, in order to monitor and quantify changes in ocean structure.

}, author = {Elizabeth Weidner} } @article {7220, title = {An Acoustic Scattering Model for Stratification Interfaces}, volume = {150(6)}, year = {2021}, month = {December}, pages = {4353-4361}, publisher = {Acoustic Society of America}, abstract = {

Stable fluid bodies, such as the ocean and atmosphere, are composed of a series of increasingly dense layers, defined by density stratification interfaces in which the medium properties (e.g., temperature, salinity) change. The intensity of the stratification between the layers influences the internal mixing dynamics and entrainment, facilitating the transport of dissolved constituents within the fluid medium. Acoustic systems offer the means for high resolution observations of these interfaces, which allow for continuous data collection over broad spatial scales. Here, a one-dimensional acoustic scattering model is presented for predicting acoustic backscatter from stratification interfaces, which is widely applicable to the acoustic water column data collected with ship-mounted sonars. Model predictions based on hydrographic profiles suggest that in many oceanic cases, the density gradient perturbations can be disregarded, and sound speed perturbations alone drive the majority of the acoustic scattering. A frequency-dependent scattering intensity based on the sharpness of the stratification interface is predicted by the model, suggesting a path to remote estimations of the physical medium properties through broadband acoustic inversion.

}, doi = {10.1121/10.0009011}, author = {Elizabeth Weidner and Thomas C Weber} } @article {7219, title = {Amplified Climate Sensitivity of Northern Greenland Fjords through Sea-Ice Damming}, volume = {2(70)}, year = {2021}, month = {April 12}, abstract = {

Record-high air temperatures were observed over Greenland in the summer of 2019 and melting of the northern Greenland Ice Sheet was particularly extensive. Here we show, through direct measurements, that near surface ocean temperatures in Sherard Osborn Fjord, northern Greenland, reached 4\ \°C in August 2019, while in the neighboring Petermann Fjord, they never exceeded 0\ \°C. We show that this disparity in temperature between the two fjords occurred because thick multi-year sea ice at the entrance of Sherard Osborn Fjord trapped the surface waters inside the fjord, which led to the formation of a warm and fresh surface layer. These results suggest that the presence of multi-year sea ice increases the sensitivity of Greenland fjords abutting the Arctic Ocean to climate warming, with potential consequences for the long-term stability of the northern sector of the Greenland Ice Sheet.

}, doi = {https://doi.org/10.1038/s43247-021-00140-8}, author = {Christian Stranne and Johan Nilsson and Adam Ulfsbo and Matt O{\textquoteright}Regan and Helen K. Coxall and Lorenz Merie and Julia Muchowski and Larry A Mayer and Volker Br{\"u}chert and Jonas Fredriksson and Brett Thornton and Julek Chawarski and Gabriel West and Elizabeth Weidner and Martin Jakobsson} } @article {7016, title = {How Are ASA Students Being Impacted by the Pandemic?}, volume = {Summer}, year = {2021}, month = {March 29}, url = {https://acousticstoday.org/covid-pandemic-and-its-impact-on-asa-members/}, author = {Hilary Kates Varghese and Kieren H. McCord and Mallory Morgan and Elizabeth Weidner} } @proceedings {7082, title = {Remote Estimations of Seafloor Gas Flux Using Broadband Acoustics}, year = {2021}, month = {June 21-24}, address = {Virtual}, abstract = {

Free gas bubbles escape from the seafloor worldwide and transport greenhouse gases, such as methane and carbon dioxide, into the ocean and potentially the atmosphere. These greenhouse gas emissions influence climate, contribute to upper ocean acidification, and are vital to the development of chemosynthetic biological communities. While direct observation and sampling by remotely operated vehicles (ROVs) or cable-operated camera systems help to generate quantitative estimates of gas flux, the spatial footprint and cost of such measurements prohibits rapid, large-scale, continuous gas flux estimation. Remote sensing of gas bubbles via acoustic systems offers the opportunity for surveying over much larger spatial scales at greatly reduced cost; however, without direct information about bubble parameters (e.g. size, number, composition) quantitative flux measurements cannot be made with acoustic systems alone. Consequently, quantitative gas flux estimates are rare and gas seeps remain a poorly constrained contributor to the global carbon cycle. Here, we describe an acoustic method for the remote quantification of seafloor gas flux that was developed and applied to a hydrothermal seep system in the Bay of Plenty, New Zealand. This method utilizes a calibrated broadband split-beam echo sounder to discriminate individual bubbles using high vertical range resolution and remotely estimate the bubble size distribution (BSD) of seeps. Additionally, split-beam phase differentiation provides phase-angle data, used to compensate for beam-pattern effects and deliver calibrated target strength measurements for individual seeps. Together with gas composition, individual seep BSD and target strength measurements provide a path, through acoustic inversion, for remote quantification of seafloor gas flux. Following this approach, the carbon dioxide release from a seep system in the Bay of Plenty was estimated to be 146 kg/day (standard deviations of 31.5 kg/day) from a seafloor area of approximately 0.25 km2.

}, author = {Elizabeth Weidner}, editor = {Thomas C Weber and Yoann Ladroit and Geoffroy Lamarche and Larry A Mayer} } @article {6790, title = {A Broadband Acoustic Study of the Spatiotemporal Variability of the Baltic Sea Anoxic Zone}, year = {2020}, month = {February 17-21}, pages = {San Diego, CA}, author = {Elizabeth Weidner and Christian Stranne and Jonas Henati Sundberg} } @article {6791, title = {Links Between Baltic Sea Submarine Terraces and Groundwater Sapping}, volume = {8}, year = {2020}, month = {January 3}, pages = {1-15}, abstract = {

Submarine Groundwater Discharge (SGD) influences ocean chemistry, circulation, spreading of nutrients and pollutants, and shapes seafloor morphology. In the Baltic Sea, SGD was linked to the development of terraces and semi-circular depressions mapped in an area of the southern Stockholm Archipelago, Sweden, in the 1990s. We mapped additional parts of the Stockholm Archipelago, areas in Blekinge, southern Sweden, and southern Finland using high-resolution multibeam sonars and sub-bottom profilers to investigate if the seafloor morphological features discovered in the 1990s are widespread and to further address the hypothesis linking SGD to their formation. Sediment coring and seafloor photography conducted with a Remote Operated Vehicle (ROV) and divers add additional information to the geophysical mapping results. We find that terraces, with general bathymetric expressions of about 1 m and lateral extents of sometimes \> 100 m, are widespread in the surveyed areas of the Baltic Sea and are consistently formed in glacial clay. Semi-circular depressions, however, are only found in a limited part of a surveyed area east of the island Ask\ö, southern Stockholm Archipelago. Our study supports the basic hypothesis of terrace formation initially proposed in the 1990s, i.e. groundwater flows through siltier permeable layers in glacial clay to discharge at the seafloor, leading to the formation of a sharp terrace when the clay layers above seepage zones are undermined enough to collapse. By linking the terraces to a specific geologic setting, our study further refines the formation hypothesis and forms the foundation for a future assessment of SGD in the Baltic Sea that may use marine geological mapping as a starting point. We propose that SGD through the sub-marine seafloor terraces is most likely intermittent and linked to periods of higher groundwater levels, implying that to quantify the contribution of freshwater to the Baltic Sea through this mechanism, more complex hydrogeological studies are required.

}, doi = {10.5194/esurf-2019-40}, author = {Martin Jakobsson and Matt O{\textquoteright}Regan and Carl-Magnus M{\"o}rth and Christian Stranne and Elizabeth Weidner and Jim Hansson and Richard Gyllencreutz and Christoph Humborg and Tina Elfwing and Alf Norkko and Joanna Norkko and Bj{\"o}rn Nilsson and Arne Sj{\"o}str{\"o}m} } @article {6937, title = {Ryder Glacier in Northwest Greenland is Shielded from Warm Atlantic Water by a Bathymetric Sill}, volume = {45}, year = {2020}, month = {November 4}, publisher = {Springer Nature}, abstract = {

The processes controlling advance and retreat of outlet glaciers in fjords draining the Greenland Ice Sheet remain poorly known, undermining assessments of their dynamics and associated sea-level rise in a warming climate. Mass loss of the Greenland Ice Sheet has increased six-fold over the last four decades, with discharge and melt from outlet glaciers comprising key components of this loss. Here we acquired oceanographic data and multibeam bathymetry in the previously uncharted Sherard Osborn Fjord in northwest Greenland where Ryder Glacier drains into the Arctic Ocean. Our data show that warmer subsurface water of Atlantic origin enters the fjord, but Ryder Glacier\’s floating tongue at its present location is partly protected from the inflow by a bathymetric sill located in the innermost fjord. This reduces under-ice melting of the glacier, providing insight into Ryder Glacier\’s dynamics and its vulnerability to inflow of Atlantic warmer water.

}, doi = {https://doi.org/10.1038/s43247-020-00043-0}, author = {Martin Jakobsson and Larry A Mayer and Johan Nilsson and Christian Stranne}, editor = {Brian R Calder and Matt O{\textquoteright}Regan and John Farell and Thomas M. Cronin and Volker Br{\"u}chert and Julek Chawarski and Bjorn Eriksson and Jonas Fredriksson and Laura Gemery and Anna Glueder and Felicity A. Holmes and Kevin Jerram and Nina Kirchner and Alan Mix and Julia Muchowski and Abhay Prakash and Brendan Reilly and Brett Thornton and Adam Ulfsbo and Elizabeth Weidner and Henning {\r A}kesson and Tamara Handl and Emelie St{\r a}hl and Lee-Gray Boze and Samuel Reed and Gabriel West and June Padman} } @article {6966, title = {Student and Regional Chapters: The Grass Roots of the ASA}, volume = {16,4}, year = {2020}, month = {December 9}, pages = {3}, publisher = {Acoustical Society of America}, address = {Melville, NY}, url = {https://acousticstoday.org/student-and-regional-chapters-the-grass-roots-of-the-asa-colby-w-cushing-and-elizabeth-f-weidner/}, author = {Colby W. Cushing and Elizabeth Weidner} } @article {6933, title = {Tracking the Spatiotemporal Variability of the Oxic{\textendash}Anoxic Interface in the Baltic Sea with Broadband Acoustics}, year = {2020}, month = {03 November 2020}, abstract = {

Anoxic zones, regions of the water column completely devoid of dissolved oxygen, occur in open oceans and coastal zones worldwide. The Baltic Sea is characterized by strong salinity-driven stratification, maintained by occasional water inflows from the Danish Straights and freshwater input from rivers. Between inflow events, the stratification interface between surface and deep waters hinders mixing and ventilation of deep water; consequently, the bottom waters of large regions of the Baltic are anoxic. The onset of the anoxic zone is closely coincident with the depth of the halocline and, as a result, the interface between oxic and anoxic waters corresponds to a strong impedance contrast. Here, we track acoustic scattering from the impedance contrast utilizing a broadband split-beam echosounder in the Western Gotland Basin and link it to a dissolved oxygen level of 2 ml/l using ground truth stations. The broadband acoustic dataset provides the means to remotely observe the spatiotemporal variations in the oxic\–anoxic interface, map out the extent of the anoxic zone with high resolution, and identify several mechanisms influencing the vertical distribution of oxygen in the water column. The method described here can be used to study other systems with applications in ongoing oceanographic monitoring programs.

}, keywords = {anoxia, Baltic Sea, Broadband acoustics, climate change, coastal, hypoxia, stratification}, doi = {10.1093/icesjms/fsaa153}, url = {https://academic.oup.com/icesjms/advance-article/doi/10.1093/icesjms/fsaa153/5952886?guestAccessKey=a0ae8696-7215-4e71-a8c5-bbd38fbb1a77}, author = {Elizabeth Weidner and Christian Stranne and Jonas Henati Sundberg and Thomas C Weber and Larry A Mayer and Martin Jakobsson} } @article {6792, title = {Bathymetric Properties of the Baltic Sea}, volume = {15(4)}, year = {2019}, month = {July 16}, pages = {905-924}, abstract = {

Marine science and engineering commonly require reliable information about seafloor depth (bathymetry), e.g. for studies of ocean circulation, bottom habitats, fishing resources, sediment transport, geohazards and site selection for platforms and cables. Baltic Sea bathymetric properties are analysed here using the using the newly released Digital Bathymetric Model (DBM) by the European Marine Observation and Data Network (EMODnet). The analyses include hypsometry, volume, descriptive depth statistics, and km-scale seafloor ruggedness, i.e. terrain heterogeneity, for the Baltic Sea as a whole as well as for 17 sub-basins defined by the Baltic Marine Environment Protection Commission (HELCOM). We compare the new EMODnet DBM with IOWTOPO, the previously most widely used DBM of the Baltic Sea which has served as the primary gridded bathymetric resource in physical and environmental studies for nearly two decades. The area of deep water exchange between the Bothnian Sea and the Northern Baltic Proper across the \Åland Sea is specifically analysed in terms of depths and locations of critical bathymetric sills. The EMODnet DBM provides a bathymetric sill depth of 88 m at the northern side of the \Åland Sea and 60 m at the southern side, differing from previously identified sill depths of 100 and 70 m respectively. High-resolution multibeam bathymetry acquired from this deep water exchange path, where vigorous bottom currents interacted with the seafloor, allows us to assess what we are missing in presently available DBMs in terms of physical characterisation and our ability to then interpret seafloor processes and highlights the need for continued work towards complete high-resolution mapping of the Baltic Sea seafloor.

}, doi = {10.5194/os-2019-18}, author = {Martin Jakobsson and Christian Stranne and Matt O{\textquoteright}Regan and Sarah Greenwood and Bo Gustafsson and Christoph Humborg and Elizabeth Weidner} } @article {6803, title = {Echoes from the Ocean{\textquoteright}s Interior: High-Frequency Observations of Ocean Phenomena}, volume = {145(3)}, year = {2019}, month = {April 23}, pages = {1653-1653}, publisher = {Acoustical Society of America}, abstract = {

Recent technological advances in high-frequency (\>10 kHz) sonar transducers, sonar transceivers, and sonar design have been accompanied by increased capabilities for observing ocean phenomena. These advances include the high range resolution and frequency-domain target classification capabilities associated with wideband acoustic echo sounders, the long-range high-resolution synoptic imaging capabilities associated with multibeam echo sounders and synthetic aperture sonar, and an increased focus on sensor calibration for all systems. High-frequency sonars are increasingly being used to quantify ocean phenomena at scales ranging from sub-centimeter (e.g., individual gas bubbles) to 100s of km (e.g., internal waves) to several 10s of km (e.g., thermohaline staircases). In this talk, we highlight some of the ocean processes that we have been investigating using high-frequency sonar systems, typically involving the transport of hydrocarbons, heat, energy, and fresh water into and through the ocean, and some of the (many) acoustic challenges that must be overcome to continue to increase the value of these observations.

}, doi = {10.1121/1.5101062}, author = {Thomas C Weber and Larry A Mayer and Anthony P. Lyons and Loranger, Scott and Alexandra M Padilla and Elizabeth Weidner} } @article {6793, title = {Tracking the Spatiotemporal Variability of the Oxic-Anoxic Interface in the Baltic Sea with Broadband Acoustics}, year = {2019}, month = {December 2-6}, pages = {San Diego, CA}, author = {Elizabeth Weidner and Christian Stranne and Jonas Henati Sundberg} } @article {6494, title = {A Wideband Acoustic Method for Direct Assessment of Bubble-Mediated Methane Flux}, volume = {173}, year = {2019}, month = {February 1}, pages = {104-115}, publisher = {Elsevier}, abstract = {

The bubble-mediated transport and eventual fate of methane escaping from the seafloor is of great interest to researchers in many fields. Acoustic systems are frequently used to study gas seep sites, as they provide broad synoptic observations of processes in the water column. However, the visualization and characterization of individual gas bubbles needed for quantitative studies has routinely required the use of optical sensors which offer a limited field of view and require extended amounts of time for deployment and data collection. In this paper, we present an innovative method for studying individual bubbles and estimating gas flux using a calibrated wideband split-beam echosounder. The extended bandwidth (16 \– 26 kHz) affords vertical range resolution of approximately 7.5 cm, allowing for the differentiation of individual bubbles in acoustic data. Split-aperture processing provides phase-angle data used to compensate for transducer beam-pattern effects and to precisely locate bubbles in the transducer field of view. The target strength of individual bubbles is measured and compared to an analytical scattering model to estimate bubble radius, and bubbles are tracked through the water column to estimate rise velocity. The resulting range of bubble radii (0.68\–8.40 mm in radius) agrees with those found in other investigations with optical measurements, and the rise velocities trends are consistent with published models. Together, the observations of bubble radius and rise velocity offer a measure of gas flux, requiring nothing more than vessel transit over a seep site, bypassing the need to deploy time-consuming and expensive optical systems.

}, keywords = {Broadband acoustics, Bubble fate, East Siberian Arctic Ocean, Ebullition, Gas flux, Methane gas bubbles, swerus-c3}, doi = {https://doi.org/10.1016/j.csr.2018.12.005}, url = {https://www.sciencedirect.com/science/article/pii/S0278434318303649?via\%3Dihub}, author = {Elizabeth Weidner and Thomas C Weber and Larry A Mayer and Martin Jakobsson and Denis Chemykh and Semiltov, I.} } @article {6345, title = {Acoustic Mapping of Mixed Layer Depth}, volume = {14, 3}, year = {2018}, month = {June 22}, pages = {503-514}, abstract = {

The ocean surface mixed layer is a nearly universal feature of the world oceans. Variations in the depth of the mixed layer (MLD) influences the exchange of heat, fresh water (through evaporation), and gases between the atmosphere and the ocean and constitutes one of the major factors controlling ocean primary production as it affects the vertical distribution of biological and chemical components in near-surface waters. Direct observations of the MLD are traditionally made by means of conductivity, temperature, and depth (CTD) casts. However, CTD instrument deployment limits the observation of temporal and spatial variability in the MLD. Here, we present an alternative method in which acoustic mapping of the MLD is done remotely by means of commercially available ship-mounted echo sounders. The method is shown to be highly accurate when the MLD is well defined and biological scattering does not dominate the acoustic returns. These prerequisites are often met in the open ocean and it is shown that the method is successful in 95 \% of data collected in the central Arctic Ocean. The primary advantages of acoustically mapping the MLD over CTD measurements are (1) considerably higher temporal and horizontal resolutions and (2) potentially larger spatial coverage.

}, doi = {10.5194/os-14-503-2018}, url = {https://www.ocean-sci.net/14/503/2018/os-14-503-2018-discussion.html}, author = {Christian Stranne and Larry A Mayer and Martin Jakobsson and Elizabeth Weidner and Kevin Jerram and Thomas C Weber and Andersson, Leif and Johan Nilsson and Bjork, G and Katarina G{\r a}rdfeldt} } @article {6794, title = {Broadband Acoustic Observations of Individual Naturally Occurring Hydrate-Coated Bubbles in the Gulf of Mexico}, year = {2018}, month = {November 3-9}, pages = {Victoria, BC}, author = {Elizabeth Weidner and Kevin Jerram and Thomas C Weber} } @mastersthesis {6485, title = {A Wideband Acoustic Method for Direct Assessment of Bubble-Mediated Methane Flux}, volume = {Earth Sciences/Ocean Mapping}, year = {2018}, month = {May 1}, pages = {122}, school = {Univeristy of New Hampshire}, address = {Durham, NH}, abstract = {

The bubble-mediated transport and eventual fate of methane escaping from the seafloor is of great interest to researchers in many fields. Acoustic systems are frequently used to study gas seep sites, as they provide broad synoptic observations of processes in the water column. However, the visualization and characterization of individual gas bubbles needed for quantitative studies has routinely required the use of optical sensors which offer a limited field of view and require extended amounts of time for deployment and data collection. In this paper, we present an innovative method for studying individual bubbles and estimating gas flux using a calibrated wideband split-beam echosounder. The extended bandwidth (16 \– 26 kHz) affords vertical ranges resolution of approximately 7.5 cm, allowing for the differentiation of individual bubbles in acoustic data. Split-aperture processing provides phase-angle data used to compensate for transducer beam-pattern effects and to precisely locate bubbles in the transducer field of view. The target strength of individual bubbles is measured and compared to an analytical scattering model to estimate bubble radius, and bubbles are tracked through the water column to estimate rise velocity. The resulting range of bubble radii (0.68-8.40 mm in radius) agrees with those found in other investigations with optical measurements, and the rise velocities trends are consistent with published models. Together, the observations of bubble radius and rise velocity offer a measure of gas flux, requiring nothing more than vessel transit over a seep site, bypassing the need to deploy time-consuming and expensive optical systems.\ 

}, author = {Elizabeth Weidner} } @article {6217, title = {Acoustic Mapping of Thermohaline Staircases in the Arctic Ocean}, volume = {7:15192}, year = {2017}, month = {November 9}, pages = {1-9}, publisher = {Springer Nature}, abstract = {

Although there is enough heat contained in inflowing warm Atlantic Ocean water to melt all Arctic sea ice within a few years, a cold halocline limits upward heat transport from the Atlantic water. The amount of heat that penetrates the halocline to reach the sea ice is not well known, but vertical heat transport through the halocline layer can significantly increase in the presence of double diffusive convection. Such convection can occur when salinity and temperature gradients share the same sign, often resulting in the formation of thermohaline staircases. Staircase structures in the Arctic Ocean have been previously identified and the associated double diffusive convection has been suggested to influence the Arctic Ocean in general and the fate of the Arctic sea ice cover in particular. A central challenge to understanding the role of double diffusive convection in vertical heat transport is one of observation. Here, we use broadband echo sounders to characterize Arctic thermohaline staircases at their full vertical and horizontal resolution over large spatial areas (100\ s of kms). In doing so, we offer new insight into the mechanism of thermohaline staircase evolution and scale, and hence fluxes, with implications for understanding ocean mixing processes and ocean-sea ice interactions.

}, doi = {10.1038/s41598-017-15486-3}, url = {https://www.nature.com/articles/s41598-017-15486-3}, author = {Christian Stranne and Larry A Mayer and Thomas C Weber and Ruddick, Barry R and Martin Jakobsson and Kevin Jerram and Elizabeth Weidner and Johan Nilsson and Katarina G{\r a}rdfeldt} } @article {6796, title = {Advancement in the Estimation of Gas Seep Flux from Echosounder Measurements}, year = {2017}, month = {March 20-23}, pages = {Galveston, TX}, author = {Elizabeth Weidner and Larry A Mayer and Thomas C Weber} } @article {6246, title = {Implementation of an Acoustic-based Methane Flux Estimation Methodology in the Eastern Siberian Arctic Sea }, year = {2017}, month = {December 11-15}, pages = {New Orleans, LA}, abstract = {

Quantifying methane flux originating from marine seep systems in climatically sensitive regions is of critically importance for current and future climate studies. Yet, the methane contribution from these systems has been difficult to estimate given the broad spatial scale of the ocean and the heterogeneity of seep activity. One such region is the Eastern Siberian Arctic Sea (ESAS), where bubble release into the shallow water column (\<40 meters average depth) facilitates transport of methane to the atmosphere without oxidation. Quantifying the current seep methane flux from the ESAS is necessary to understand not only the total ocean methane budget, but also to provide baseline estimates against which future climate-induced changes can be measured.

At the 2016 AGU fall meeting, we presented a new acoustic-based flux methodology using a calibrated broadband split-beam echosounder. The broad (14-24 kHz) bandwidth provides a vertical resolution of 10 cm, making possible the identification of single bubbles. After calibration using 64 mm copper sphere of known backscatter, the acoustic backscatter of individual bubbles is measured and compared to analytical models to estimate bubble radius. Additionally, bubbles are precisely located and traced upwards through the water column to estimate rise velocity. The combination of radius and rise velocity allows for gas flux estimation.

Here, we follow up with the completed implementation of this methodology applied to the Herald Canyon region of the western ESAS. From the 68 recognized seeps, bubble radii and rise velocity were computed for more than 550 individual bubbles. The range of bubble radii, 1-6 mm, is comparable to those published by other investigators, while the radius dependent rise velocities are consistent with published models. Methane flux for the Herald Canyon region was estimated by extrapolation from individual seep flux values.

}, url = {https://agu.confex.com/agu/fm17/meetingapp.cgi/Paper/228715}, author = {Elizabeth Weidner and Thomas C Weber and Larry A Mayer} } @article {6795, title = {Investigating Bubble Transport and Fate in the Watercolumn with Calibrated Broadband Split-Beam Echosounder Data}, year = {2017}, month = {December 4-8}, pages = {New Orleans, LA}, author = {Elizabeth Weidner and Thomas C Weber and Larry A Mayer} } @article {6247, title = {A Multi-Frequency Investigation of the Influences of Groundwater Discharge on Hydrocarbon Emission and Transport in the Baltic Sea}, year = {2017}, month = {December 11-15}, pages = {New Orleans, LA}, abstract = {

In nearshore coastal regions submarine groundwater discharge is a major component of the hydro-geological cycle: transporting nutrients and pollutants to the ocean, producing up-welling currents through buoyancy effects, and acting as an erosional force at discharge sites. In nearshore regions where biogenic gas production is high, groundwater discharge could potentially act as a control on hydrocarbon emission and transport from the seafloor though the water-column.

In the southern Stockholm Archipelago of the Baltic Sea, terraces and semi-circular depressions on shallow (\<20 meters) seafloor have been linked to the discharge of ground water, traveling along the permeable layers in glacial clay deposits (S\öderberg and Flod\én 1995; Jakobsson et al., 2016). Sub-bottom profiles over the same region have identified widespread areas of subsurface blanking, commonly attributed to gas, as well as water-column seep features, both in spatial proximity to the groundwater discharge sites.

High-resolution multibeam bathymetry and chirp sub-bottom profiles were combined with water-column data sets collected at multiple frequencies (300 kHz, 45-90 kHz, 160-260 kHz) to map the spatial distribution of seeps and investigate their relationship to localized groundwater discharge as determined by seafloor and subsurface morphology. The spatial extent of seep sites appears closely tied to regions of suspected groundwater discharge, suggesting direct or indirect controls on gas emission pathways. Additionally, seep morphology in the broadband data hints at the possibility of groundwater and gas flow mixing.

}, url = {https://agu.confex.com/agu/fm17/meetingapp.cgi/Paper/230878}, author = {Elizabeth Weidner and Martin Jakobsson and Nycander, J and Larry A Mayer} } @article {6804, title = {Observing the Evolution and Fate of Free Methane in the Ocean}, volume = {142(4)}, year = {2017}, month = {November 15}, pages = {2505-2505}, publisher = {Acoustical Society of America}, abstract = {

Free methane gas is increasingly observed escaping the seabed in the world\’s oceans from sources that are either biogenic, typically in shallow sediments, or from deeper geologic reservoirs. Methane gas bubbles undergo a complicated journey as they rise toward the sea surface. Some or all of the methane may pass through the gas-liquid boundary, into aqueous solution, where it is eventually oxidized and can impact ocean chemistry. Some of the methane, particularly in shallow environments, may reach the atmosphere where it acts as a strong greenhouse gas. One of the key questions regarding the transport of methane upward from the seabed is how much goes where, and this question is being increasingly addressed using acoustic remote sensing techniques. Answering this question begins with seep detection and localization, now routinely performed on data collected with split-beam and multibeam echo sounders. Once located, observations of the bubble-plume backscattering cross section can be used to address questions of flux and vertical gas transport. Both narrow- and broad-band techniques and some of the associated challenges, including wobbly bubbles and multiple scattering in dense plumes, will be discussed.

}, doi = {10.1121/1.5014146}, author = {Thomas C Weber and Elizabeth Weidner and Alexandra M Padilla and Kevin M Rychert and Loranger, Scott} } @article {5798, title = {Acoustic and Geomorphological Signatures of Gas Seeps on the East Siberian Margin}, year = {2016}, month = {April 11-12}, address = {University of New Hampshire, Durham, NH}, abstract = {

Rising hydrocarbon gas concentrations in the atmosphere are strongly linked to global warming. In the next century, significant amounts of hydrocarbons will be transport from the ocean to the atmosphere via thawing of flooded permafrost. The East Siberian Arctic Shelf (ESAS) holds 80\% of the world\’s flooded permafrost and is at risk of massive release due to bottom water warming. Gas released from permafrost is transported by gas seeps through the ocean; however, the magnitude of this gas flux has historically been difficult to quantify.

This research aims to estimate the total gas flux from a region of the ESAS, Herald Canyon, via acoustic and geomorphological characterization of gas seeps in the area. Data was collected with three acoustic systems (EM122 multibeam echosounder, SBP120 subbottom profiler, and EK80 split-beam sonar) onboard the Oden during the Swedish-Russian-US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions (SWERUS-C3) program.

53 seeps have been identified in the vicinity of Herald Canyon. Together, the EM122 high-resolution multibeam bathymetry and SBP120 chirp subbottom profiling data, provide the spatial and geologic context of the gas seeps. The EK80, which makes acoustic measurements over a broad range of frequencies, can identify individual bubble scatters. This enables estimates of bubble size distribution and rise velocity measurements in certain seeps; ultimately providing gas flux estimates. The combination of three data sets offers the opportunity to link seep flux estimates to geomorphological setting. The geomorphological setting can further be linked to local and regional geologic processes determined from seafloor morphology and subsurface structure. These links will help define our knowledge of the transport of hydrocarbon gas from flooded permafrost to the atmosphere.

}, keywords = {acoustic, east siberian margin, gas seeps, geomorphological signatures}, author = {Elizabeth Weidner and Larry A Mayer and Kevin Jerram and Thomas C Weber and Martin Jakobsson and Chernykh, D. and Ananiev, R. and Mohammad, R. and Semiltov, I.} } @article {5999, title = {Quantification of Methane Gas Flux and Bubble Fate on the Eastern Siberian Arctic Shelf Utilizing Calibrated Split-beam Echosounder Data}, year = {2016}, month = {December 12-16}, pages = {San Francisco, CA}, abstract = {

On the Eastern Siberian Arctic Shelf (ESAS) subsea permafrost, shallow gas hydrates, and trapped free gas hold an estimated 1400 Gt of methane. Recent observations of methane bubble plumes and high concentrations of dissolved methane in the water column indicate methane release via ebullition. Methane gas released from the shallow ESAS (\<50 m average depth) has high potential to be transported to the atmosphere.

To directly and quantitatively address the magnitude of methane flux and the fate of rising bubbles in the ESAS, methane seeps were mapped with a broadband split-beam echosounder as part of the Swedish-Russian-US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions program (SWERUS-C3). Acoustic measurements were made over a broad range of frequencies (16 to 29 kHz). The broad bandwidth provided excellent discrimination of individual targets in the water column, allowing for the identification of single bubbles. Absolute bubble target strength values were determined by compensating apparent target strength measurements for beam pattern effects via standard calibration techniques. The bubble size distribution of seeps with individual bubble signatures was determined by exploiting bubble target strength models over the broad range of frequencies. For denser seeps, with potential higher methane flux, bubble size distribution was determined via extrapolation from seeps in similar geomorphological settings. By coupling bubble size distributions with rise velocity measurements, which are made possible by split-beam target tracking, methane gas flux can be estimated.

Of the 56 identified seeps in the SWERUS data set, individual bubbles scatterers were identified in more than half (31) of the seeps. Preliminary bubble size distribution results indicate bubble radii range from 0.75 to 3.0 mm, with relatively constant bubble size distribution throughout the water column. Initial rise velocity observations indicate bubble rise velocity increases with decreasing depth, seemingly independent of bubble radius.

}, keywords = {flux and bubble fate, methane gas, siberian arctic}, url = {https://agu.confex.com/agu/fm16/meetingapp.cgi/Paper/122698}, author = {Elizabeth Weidner and Larry A Mayer and Martin Jakobsson and Chernykh, D. and Ananiev, R. and Thomas C Weber and Kevin Jerram and Mohammad, R. and Semiltov, I.} } @article {5797, title = {Sedimentary Analysis from the Mouth of the Great Bay Estuary: Biogenic Sediment Fraction}, year = {2016}, month = {May 18}, abstract = {

Sediments were collected from the mouth of Great Bay Estuary in New Hampshire.Their lithological and biological constitutes were examined in an effort to understand the area\’s sedimentary history. Objectives of the Smear Slide/Coarse Fraction Team (SSCFT) were to:\ 

}, keywords = {Biogenic Sediment Fraction, ESCI 854, great bay estuary, sedimentary analysis, Sedimentology}, author = {Elizabeth Weidner and Matthew Roy} } @article {5796, title = {Sedimentary Analysis from the Mouth of the Great Bay Estuary: Lithologic Analysis}, year = {2016}, month = {May 18}, keywords = {ESCI 854, great bay estuary, Lithologic Analysis, sedimentary analysis, Sedimentology}, author = {Elizabeth Weidner and Matthew Roy} } @article {5705, title = {A Multi-Frequency Look at Gas Seeps on the East Siberian Margin}, year = {2015}, month = {December 14-18}, address = {San Francisco, CA}, abstract = {

The Swedish-Russian-US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions (SWERUS-C3) is a multi-investigator, multi-disciplinary program aimed at increasing our understanding of the climate-cryosphere-carbon system of the Eastern Siberian Arctic Ocean. In 2014 SWERUS-C3 carried out a two-leg field program on the Swedish Icebreaker ODEN. A component of the SWERUS-C3 program focused on water column mapping of the spatial distribution and geologic context of gas seeps using the acoustic systems on board ODEN (12 kHz EM122 multibeam echo sounder, 2-8 kHz SBP120 subbottom profiler, and an 18 kHz EK60 split-beam sonar). On Leg 2 of the 2014 expedition, a new wideband transceiver (EK80) was added to the split-beam echo sounder and calibrated, providing the ability to measure the acoustic response of the gas seeps over a much broader range of frequencies (15-30 kHz). While the broader bandwidth unquestionably provides higher target resolution a further objective of the broadband mapping was to determine whether information on bubble size distribution could be determined so as to help model the flux of gas coming from the seeps. On Leg 2 approximately 34 seeps were mapped, mostly in the vicinity of Herald Canyon. The wide-swath, high-resolution multibeam bathymetry (from the EM122) and high-resolution chirp sub-bottom profiling (from the SBP120 multibeam sub-bottom profiler) combined with water column imaging of seeps collected at both 12 kHz (from the EM122) and 15-30 kHz (from the EK80) offer an important opportunity to understand the spatial distribution of seeps and their relationship to local and regional processes as determined from seafloor and subsurface structure, as well as to explore the potential of extracting quantitative information about the magnitude of gas transport from the seeps.\ 

}, keywords = {east siberian margin, gas seeps}, url = {http://fallmeeting.agu.org/2015/}, author = {Larry A Mayer and Elizabeth Weidner and Kevin Jerram and Thomas C Weber and Martin Jakobsson and Chernykh, D. and Ananiev, R. and Mohammad, R. and Semiltov, I.} } @article {5799, title = {A Multi-Frequency Look at Gas Seeps on the East Siberian Margin}, year = {2015}, month = {December 14-18 }, publisher = {American Geophysical Union }, address = {San Francisco, CA}, abstract = {

The Swedish-Russian-US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions (SWERUS-C3)is a multi-investigator, multi-disciplinary program aimed at increasing our understanding of the climate-cryosphere-carbon system of the Eastern Siberian Arctic Ocean.In 2014, SWERUS-C3 carried out a two-leg field program on the Swedish Icebreaker ODEN. A component of the SWERUS-C3 program focused on water column mapping of the spatial distribution and geologic context of gas seeps using the acoustic systems on board ODEN(12kHzEM122 multibeam echosounder, 2-8kHzSBP120 subbottom profiler, and an 18kHzEK60split-beamsonar). On Leg 2 of the 2014 expedition, a new wide-band transceiver (EK80) was added to the split-beam echosounder and calibrated, providing the ability to measure the acoustic response of the gas seeps over a much broader range of frequencies (15-30kHz). While the broader bandwidth unquestionably provides higher target resolution, a further objective of the broadband mapping was to determine whether information on bubble size distribution could be determined so as to help model the flux of gas coming from the seeps. On Leg2, 53seeps were identified in the vicinity of Herald Canyon.The wide-swath, high-resolution multibeam bathymetry (from the EM122) and high-resolution chirp subbottom profiling (from the SBP120 multibeam subbottom profiler), combined with water column imaging of seeps collected at both 12kHz (from the EM122) and 15-30kHz (from the EK80) offer an important opportunity to understand the spatial distribution of seeps and their relationship to local and regional processes as determined from seafloor and subsurface structure, as well as to explore the potential of extracting quantitative information about the magnitude of gas transportfrom the seeps.

}, keywords = {east siberian margin, gas seeps}, url = {http://ccom.unh.edu/publications/multi-frequency-look-gas-seeps-east-siberian-margin}, author = {Elizabeth Weidner and Larry A Mayer and Thomas C Weber and Martin Jakobsson and Chernykh, D. and Ananiev, R. and Mohammad, R. and Semiltov, I.} }