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Glacier ice loss impacts sound propagation within Arctic fjords. Regular calving events contribute to a collection of floating ice fragments, known as brash ice, at the ocean surface that obstruct the natural and anthropogenic acoustic signals, yet are difficult to characterize. Transmission loss measurements using a maximum length sequence ( m-sequence) signal were conducted in September 2017 near Hansbreen glacier in Hornsund Fjord, Svalbard with dense brash ice present at the water surface. An acoustic model of the brash ice surface was inferred through consideration of the experimental geometry, arrival amplitude, and travel time difference between the direct and surface reflected arrivals from the source to two receivers. The inferred surface was then incorporated into a forward simulation of the environment using sound speed profiles measured during the experiment. BELLHOP ([Porter and Bucker (1987). J. Acoust. Soc. Am. 82(4), 1349-1359],), a ray tracing code available in the Acoustics Toolbox (HLS Inc., San Diego, CA), was used to track the time difference of arrivals and amplitudes of the modeled direct and surface reflected rays. Comparisons between the measured and simulated results provide insight into the geometric shape and reflection characteristics of the brash ice surface within this and similar environments.

Climate shifts are particularly conspicuous in the Arctic. Satellite and terrestrial observations show significant increases in the melting and breakup of Arctic tidewater glaciers and their influence on sea level rise. Increasing melt rates are creating an urgency to better understand the link between atmospheric and oceanic conditions and glacier frontal ablation through iceberg calving and melting. Elucidating this link requires a combination of short and long-time scale measurements of terminus activity. Recent work has demonstrated the potential of using underwater sound to quantify the time and scale of calving events to yield integrated estimates of ice mass loss (Glowacki and Deane, 2020). Here, we present estimates of subaerial calving flux using underwater sound recorded at Hansbreen, Svalbard in September 2013 combined with an algorithm for the automatic detection of calving events. The method is compared with ice calving volumes estimated from geodetic measurements of the movement of the glacier terminus and an analysis of satellite images. The total volume of above-water calving during the 26 days of acoustical observation is estimated to be 1.7 ± 0.7 × 107 m3, whereas the subaerial calving flux estimated by traditional methods is 7 ± 2 × 106 m3. The results suggest that passive cryoacoustics is a viable technique for long-term monitoring of mass loss from marine-terminating glaciers.

Submarine-melting of ice at the glacier-ocean interface accounts for a large portion of the ice-loss at tidewater glaciers and produces sound via bubble-release. The sound production is dominant in the sub-surface region near the glacier-ocean interface. This depth-dependence of the sound is studied by melting ice blocks in a glacial bay at various depths up to 20 m and recording their acoustics over a large frequency range. The acoustic energy decreases with depth in line with expectations from the physics of the phenomenon and is fit to an exponentially decaying curve. The estimated variation will be useful for interpreting the sound in marine-terminating glaciers bays in terms of the submarine-melting activity.

Climate-change induced melting is leading to accelerating ice loss at tidewater glaciers worldwide. A significant component of the freshwater flux from these glaciers arises from submarine melting at the glacier-ocean interface. This melting causes a distinct acoustic signature due to the release of pressurized bubbles underwater, opening up the possibility of monitoring this phenomenon on a large scale using passive acoustic systems. To evaluate the use of sound in monitoring submarine glacier melting, we made acoustic measurements using vertical hydrophone arrays in four glacial bays in Svalbard in 2019. As the recording array was moved away from the glacier, the variation in the recorded acoustic level due to melting ice did not follow a uniformly decreasing trend as one might expect. Moreover, the acoustic intensities at different glaciers were clustered at different levels. These observations indicate that the geometry of the glacier-ocean interface, thermohaline structure of the underwater channel and presence of floating ice in the bay played a role in determining the acoustic field. Most of this variation can be explained through propagation modeling. Moving forward, this model-based interpretation of the field will play an integral part in inverting the sound to estimate the submarine melt rate.

Arctic glacial bays are among the loudest natural environments in the ocean, owing to heavy submarine melting, calving, freshwater discharge, and ice–wave interactions. Understanding the coherence and vertical directionality of the ambient sound there can provide insights about the mechanisms behind the ice loss in these regions. It can also provide key information for operating technologies such as sonar, communication, and navigation systems. To study the unexplored sound coherence and vertical directionality in glacial bays, a vertical hydrophone array was deployed, and acoustic measurements were made at four glacier termini in Hornsund Fjord, Spitsbergen, in June and July 2019. The measurements show that the sound generated by melting glacier ice is more dominant in the upper portion of the water column near the glacier terminus. The melt water from the submarine melting and the freshwater discharge from the glacier create a glacially modified water duct near the sea surface. This disrupts the inter-sensor vertical coherence in the channel. However, some coherence across the duct is preserved for sound arising from spatially localized events at low frequencies. Overall, the observations in this study can help improve the understanding of the submarine melting phenomenon in glacial bays.

The underwater noise emission from glacier calving is investigated by integrating acoustic and photographic observations made in a glacial bay and model pool. Similarities in the impact noise in these two settings are identified. Distinct fluid-dynamics processes are involved in sound generation: iceberg detachment, water entry, entrainment and collective oscillation of a bubble cloud, secondary impacts due to splashes, and calving-induced wave action. The lag between initial impact and bubble plume pinch-off from the subsurface cavity depends on ice block dimensions and drop height and may be useful in reducing errors in estimates of calving fluxes made using underwater sound.

Summary: Tidewater glaciers supply large amounts of suspended particulate matter (SPM) and freshwater to fjords and affect oceanographic, sedimentological and biological processes. Our understanding of these processes, is usually limited to the short summer season. Here, we present the results of a one-year-long monitoring of the spatial variability in SPM characteristics in a context of oceanographic and meteorological conditions of a glacial bay next to Hansbreen, a tidewater glacier in Hornsund (southern Spitsbergen). The observed range of SPM concentrations was similar to ranges measured in other sub-polar glaciated fjords, especially in Svalbard. The major source of SPM is the meltwater discharge from the glacier. The maximum water column-averaged SPM concentrations did not correlate with peaks in freshwater discharge and were observed at the beginning of the autumn season, when the fjord water transitioned from stratified to fully mixed. The observed spatiotemporal variations in the total SPM, particulate organic matter (POM) and particulate inorganic matter (PIM) are likely controlled by a combination of factors including freshwater supply, water stratification and circulation, bathymetry, the presence of sea ice, biological productivity and sediment resuspension. During the ablation season, the SPM maximum concentrations were located within the upper water layer, whereas during the winter and spring, the greatest amounts of SPM were concentrated in deeper part. Thus, typical remote sensing-based studies that focus on SPM distributions may not reflect the real SPM levels. POM and PIM concentrations were correlated with each other, during most of the time suggesting that they may have a common source. Keywords: Seasonality, Suspended particulate matter, Particulate organic matter, Tidewater glacier, Fjord, Svalbard

Ice sheets are expected to be major contributors to sea level rise in the coming decades and centuries. Ocean-forced melting at marine terminating glaciers has the potential to be an important driver of mass loss from these ice sheets, but is difficult to measure directly using conventional techniques, and thus remains poorly understood. The air pressure in bubbles trapped in glacier ice is typically greater than the hydrostatic pressure near the surface of the water. This pressure difference causes the bubbles to expand rapidly and radiate sound when they are released as the ice melts. This sound presents a promising signal which could be used to make passive acoustic measurements of submarine melting at glacier termini, if it can be characterized sufficiently. Prior work has demonstrated that there is considerable variability in the acoustic energy radiated by the release of individual bubbles. Here we show that the total acoustic energy radiated by small blocks of glacier ice as they melt is correlated with the total potential energy stored by the compressed air bubbles in the ice. We find that the conversion efficiency is highest for the most energetic blocks of ice, and present some modelling efforts to explain this trend.

Transmission loss measurements were conducted in the meltwater-modified surface layer near Hansbreen Glacier in Hornsund Fjord in southwestern Svalbard in September 2017 [Deane and Glowacki, JASA 143, 1711 (2018)]. An ITC-1007 (International Transducer Corporation) source emitting an m-sequence signal (149 dB re 1 µPa, 11 kHz carrier frequency) was tethered at 6.7 m depth to a boat allowed to drift 20 m to 200 m from a pair of stationary receivers. These two receivers, HTI-96-Min hydrophones (High Tech, Inc.), were tethered at 8 and 17 m to a buoy anchored 500 m from the glacier terminus. Within this environment, and typical for a glacierized fjord, regular calving events contributed to a collection of icebergs, or brash ice, at the water surface obstructing the transmission path, particularly the surface reflected path. A ray-based approach using Bellhop, a code available in the Acoustics Toolbox, was used to simulate the environment as a means of comparison to the measured data. The variability of the brash ice surface was included in the model through incorporating a simulated surface at the ocean surface. Comparisons between outcomes from increasingly complex iterations of this model with the collected data are discussed.

Measurement of the geometry of marine-terminating glaciers is challenging due to the lack of stable ground areas in close proximity to the glacier. This precludes the use of fixed measuring devices and restricts the placement of ground control points. We propose a measurement procedure for marine-terminating glaciers using structure-from-motion including proper survey planning, control point design and model alignment. As a case study, we surveyed Hans Glacier, Hornsund fjord, South Spitsbergen. We demonstrate that our method is indeed effective for documentation of small-scale glacier dynamics, show the importance of appropriate alignment strategies for models with poorly distributed control points and compare two SfM tools (Agisoft Metashape and Bentley ContextCapture) concluding that ContextCapture offers around 17% lower error, 25% faster processing and better reconstruction of fine details and shadowed concavities.

Ambient noise oceanography is proving to be an efficient and effective tool for the study of ice-ocean interactions in the bays of marine-terminating glaciers. However, obtaining quantitative estimates of ice melting or calving processes from ambient noise requires an understanding of how sound propagation through the bay attenuates and filters the noise spectrum. Measurements of the vertical structure in sound speed in the vicinity of the Hans Glacier in Hornsund Fjord, Spitsbergen, made with O(130) CTD casts between May and November 2015, reveal high-gradient, upward-refracting sound speed profiles created by cold, fresh meltwater during summer months. Simultaneous recordings of underwater ambient noise made at depths of 1, 10 and 20 meters in combination with propagation model calculations using the model Bellhop illustrate the dominant role these surface ducts play in shaping the underwater soundscape. The surface ducts lead to a higher intensity and greater variability of acoustic energy in the near-surface layer covered by glacially-modified waters relative to deeper waters, indicating deeper zones as most appropriate for inter-seasonal acoustic monitoring of the glacial melt. Surface waveguides in Hornsund are relatively shallow and trap sound above O(1 kHz). Deeper waveguides observed elsewhere will also trap low-frequency sounds, such as those generated by calving events for example. Finally, the ambient noise field in Hornsund is shown to be strongly dependent on the distribution of ice throughout the bay, stressing the importance of performing complementary environmental measurements when interpreting the results of acoustic surveys. This article is protected by copyright. All rights reserved.

Marine-terminating glaciers worldwide are melting rapidly in response to climate shifts, resulting in the delivery of freshwater into the oceans. Submarine melting at the glacier-water interface accounts for a significant component of the freshwater delivery from the glacier. This melting produces a distinct acoustic signature, providing a potentially viable modality to monitor glacial ice melting on a large scale via acoustic sensing. In order to evaluate the utility of ambient noise oceanography as a tool to quantify glacial ice-melt, in June 2019 we deployed a vertical hydrophone array and made acoustic measurements at some glacier termini in Hornsund Fjord, Spitsbergen. Quantification via array processing proves to be challenging due to (1) the space- and time-varying sound-speed profile in the underwater channel, and the way it refracts sound in an unknown manner, (2) limited vertical resolution of the array due to its aperture, and (3) interference from other noise sources such as melting icebergs, for example, contaminating the melt sound recordings. We present preliminary results from the processing which reveal different acoustic levels arising from submarine melting at different glaciers. The sound from the melt seems to be more dominant in the upper layers of the water at the glacier-sea interface.

Melting glaciers and ice sheets are important contributors to sea level rise, but the rates at which they are losing mass are difficult to measure precisely. Using the acoustic signals produced by the rapid release of pressurized air from bubbles contained in the ice is a promising avenue for obtaining quantitative estimates of the rate of submarine melting at the termini of tidewater glaciers. The amplitude and character of the observed average signal generated by the bubble release events have been found to depend strongly upon the hydrostatic pressure of the water the bubbles are released into, and therefore on the depth at which said events occur; this dependence must be better understood before the goal of measuring melting rates can be achieved. Data from field experiments performed at the Hornsund fjord in Svalbard, Norway, in which the acoustic melting signal from blocks of glacier ice was recorded at varying depths, will be presented, and compared to the output of an idealized model for the acoustic signal produced by the release of bubbles from melting ice.

Glacierized fjords are dynamic regions, with variable oceanographic conditions and complex ice-ocean interactions, which are still poorly understood. Recent studies have shown that passive underwater acoustics offers new promising tools in this branch of polar research. Here, we present results from two field campaigns, conducted in summer 2013 and spring 2014. Several recordings with a bespoke two-hydrophone acoustic buoy were made in different parts of Hornsund Fjord, Spitsbergen in the vicinity of tidewater glaciers to study the directionality of underwater ambient noise. Representative segments of the data are used to illustrate the analyses, and determine the directions of sound sources by using the time differences of arrivals between two horizontally aligned, broadband hydrophones. The results reveal that low frequency noise (< 3 kHz) is radiated mostly from the ice cliffs, while high-frequency (> 3 kHz) noise directionality strongly depends on the distribution of floating glacial ice throughout the fjord. Changing rates of iceberg production as seen for example in field photographs and logs are, in turn, most likely linked to signal amplitudes for relevant directions. These findings demonstrate the potential offered by passive acoustics to study the dynamics of individual tidewater glaciers.

Climate-driven ice-water interactions in the contact zone between marine-terminating glaciers and the ocean surface show a dynamic and complex nature. Tidewater glaciers lose volume through the poorly-understood process of calving. A detailed description of the mechanisms controlling the course of calving is essential for the reliable estimation and prediction of mass loss from glaciers. Here we present the potential of hydroacoustic methods to investigate different modes of ice detachments. High-frequency underwater ambient noise recordings are combined with synchronized, high-resolution, time-lapse photography of the Hans Glacier cliff in Hornsund Fjord, Spitsbergen to identify three types of calving events: typical subaerial, sliding subaerial and submarine. A quantitative analysis of the data reveals a robust correlation between ice impact energy and acoustic emission at frequencies below 200 Hz for subaerial calving. We suggest that relatively inexpensive acoustic methods can be successfully used to provide quantitative descriptions of the various calving types.

Transmission loss measurements were conducted in the meltwater-modified surface layer near Hansbreen Glacier in Hornsund Fjord in southwestern Svalbard in September 2017 [Deane and Glowacki, JASA 143, 1711 (2018)]. An m-sequence source signal (149 dB re 1 μPa, 11 kHz carrier frequency) was tethered at 7 m depth to a boat drifting from 0 to 200 m. This signal was received by two Hitech HTI-96 hydrophones at 8 and 17 m depth deployed from a stationary boat anchored 500 m from the glacier. Within this environment, and typical for a glacierized fjord, regular calving events contributed to an ice melange top boundary layer with larger icebergs occasionally obstructing the signal transmission path. The propagation environment was upward refracting, causing propagation sound to repeatedly reflect from the surface layer. A ray-based approach was applied to model the measured data. The variability of the top boundary was included in the model by incorporating surface scattering and inserting icebergs. Comparisons between several increasingly complex iterations of this model with the collected data will be presented. [Work supported by the NDSEG Fellowship, ONR Grant Nos. N00014-17-1-2633 and N00014-14-1-0213, and the Polish National Science Centre Grant No. 2013/11/N/ST10/01729.]

Marine-terminating glaciers are retreating at an unprecedented pace, largely as a result of enhanced submarine melting. However, studying ice-ocean interactions is complicated due to both harsh conditions prevailing in glacial bays and lack of scientific methods enabling continuous measurements. Recent studies have shown that high underwater noise levels measured in the Arctic are related to glacier melt, but quantitative research requires proper separation of individual noise sources, including icebergs and glacier fronts. Therefore, we show results of field experiments carried out in 2013, 2015, and 2016 in Hornsund fjord, Svalbard, to present directionality and statistics of the noise produced by melting icebergs. Measurements of noise directionality were conducted with 3-hydrophone acoustic array. Calculated angles of arrivals for the noise at the frequency range of 1–10 kHz correspond well to locations of individual, grounded icebergs. The amplitude of sound emitted by these sources has a symmetric α-stable distribution, with parameters depending on separation between iceberg and receiver. These findings demonstrate that ambient noise oceanography is an efficient tool to detect and track icebergs using natural noise they produce during melting. [Work funded by the Polish National Science Centre, Grant No. 2013/11/N/ST10/01729 and by ONR, Grant No. N00014-17-1-2633.]

A propagation experiment was undertaken in the meltwater-modified surface layer in the bay of a marine-terminating Arctic glacier. Broad-band, m-sequence transmissions were made with an International Transducer Corporation 1007 source deployed from a drifting boat tracked using gps, approximately 500 m in front of Hansbreen Glacier in Hornsund Fjord, Southwestern Svalbard in the summer of 2017. Signals were received with a short array of Hitech HTI-96 hydrophones tethered to an autonomous, anchored boat. The distance between the hydrophone array and source was measured every 2 minutes using a laser rangefinder. Propagation effects in this noisy and dynamic environment include waveguide propagation through the meltwater-modified surface layer and occlusion of transmissions by drifting icebergs. Details of the experiment and propagation effects noted during the transmission period will be presented and discussed. [Work funded by ONR, Grant No. N00014-17-1-2633, and by the Polish National Science Centre, Grant No. 2013/11/N/ST10/01729.]

Measurements of the vertical directionality of the sound of bubbles released explosively from a melting glacier terminus are presented. These data are motivated by a desire to infer ice melt rates using the sound generated by bubbles, trapped in the glacier ice at the base of the fern layer and pressurized over time, as they are released by the melting terminus. The free energy available to generate noise is a function of the difference between the bubble internal gas pressure and hydrostatic pressure, both of which can vary with depth beneath the sea surface. Previous studies of bubble gas pressure in glacier ice suggest that the noise generated by bubble release should decrease with increasing depth below the surface. Measurements of noise directionality made with a compact, 4-element hydrophone array approximately 300 m in front of Hansbreen Glacier in Hornsund Fjord, Southwestern Svalbard in the summer of 2017 will be presented and discussed. This study suggests that only the top few 10’s of meters of ice cliff generate the majority of melt noise. This result has important implications for the interpretation of bubble noise in terms of ice melt rate. [Work funded by ONR, Grant No. N00014-17-1-2633 and by the Polish National Science Centre, Grant No. 2013/11/N/ST10/01729.]

Field tests were carried out at a section of the River Vistula located within the boundaries of the Świderskie Islands nature reserve in order to analyse bathymetric changes at different discharge values during the period of 2012–2014. The paper shows that the dynamics and transport of sand-waves and sandbanks strongly influence the bathymetry of the riverbed at the selected cross-sections. Moreover, the impact of groynes on the bed topography is briefly discussed. Discharge measurements completed with the use of an acoustic Doppler current profiler (ADCP RiverSurveyor S5, SonTek) are also presented. Results support the values given by the Institute of Meteorology and Water Management (IMGW) at the gauging station in Gusin (461 km from the source) solely for the mean water levels. It is shown that the differences between measured values and values given by IMGW of the flow discharge ranged from 3 to 30 % of measuring values depending on the water level and discharge itself. The findings of this study may provide essential tutorial material for education in hydrology, civil engineering and environmental hydraulics as they emphasize large uncertainties inherent in hydrological modelling resulting from high dynamics of the bedload transport process.

Recent acceleration of sea ice decline observed in the Arctic Ocean draws attention to environmental factors driving this phenomenon. One of the main conclusions is a growing need for better understanding of sea ice drift, deformation, and fracturing. In response to that call, several ambient noise recordings were carried out in the coastal zone of Hornsund Fjord, Spitsbergen, in spring 2015 to study underwater acoustic signatures of sea ice behavior. The noise levels varied significantly with sea ice type and intensity of external forces. Low-frequency signatures were strongly related to tidal cycle, which manifested in much higher SPL values at low water. Compacted ice cover is periodically deformed and crushed, representing a significant contribution to the ambient noise field in the study site. Average noise levels at frequencies above 1 kHz are, in turn, considerably higher in front of marine-terminating glacier than in the neighboring, non-glacial bay. These differences, expanding with the rise of water temperature, are associated with melting of the ice cliff and generally unaffected by the presence of sea ice. [Work funded by the Polish National Science Centre, Grant No. 2013/11/N/ST10/01729.]

The directionality of ambient noise in an Arctic tidewaterglacier bay was measured using two horizontally spaced, broadbandhydrophones. Segments of noise were divided into two frequency bandsand analyzed for arrival angle. These data show that different classes ofsource radiate noise in distinct spectral bands and are spatially diverse.A previously unidentified source, the interaction of surface gravitywaves with underside of ice ledges at the periphery of icebergs, isdescribed. The generation of noise by ice-wave interaction suggests thatsurface waves should be measured if ambient noise is to be used tomonitor ice dynamics in glacial fjords.

Arctic and Southern Oceans are extremely noisy places. Various geophysical and biological processes generate underwater sounds at different frequencies. Using spectral, wavelet and statistical analysis, it becomes possible to distinguish almost all individual phenomena. This allows the assessment of, among other things, the rainfall intensity, various characteristics of wind-generated waves, abundance of marine organisms and shipping traffic. These issues are now relatively well-understood. What is more, for such studies hydroacoustic methods have been widely used for many years and provided satisfactory results. In the last decades, however, more and more attention is paid to sea-ice processes and properties, calving events and drifting icebergs. Melting ice and retreating tidewater glaciers are also sources of underwater ambient noise. This becomes more and more noticeable due to the observed climate shifts. Dynamic nature of these phenomena and harsh conditions encountered during field measurements still limit the progress in this area of research. In spite of all, recent preliminary studies show the possibility of using passive acoustic methods for both analyzing calving events in the Arctic fjords and investigating the behavior of icebergs. It became possible, for instance, to identify and describe various stages of calving processes: large rumbles, ice fractures, impacts on the water and iceberg oscillations. On the other hand, ambient noise related with freshwater outflows and sound propagation in the vicinity of glaciers are still unstudied. Moreover, underwater sounds associated with sea-ice processes occurring in small basins are also poorly understood, as well as their directivity and relationships with meteorological and oceanographic conditions. These topics require further investigation, which will enable the development of appropriate classification algorithms. For this purpose, new field experiments and methods of data analysis as well as state-of-the-art measuring devices are needed. A review of existing research articles concerning underwater cryogenic sounds is presented here, supplemented by a summary of the main gaps and suggested future needs. All papers are sorted thematically and chronologically, showing the historical development of hydroacoustic methods and approaches in this area.