Underwater Ice Research Articles

Turbulent Dynamics of Buoyant Melt Plumes Adjacent Near‐Vertical Glacier Ice

AbstractAt marine‐terminating glaciers, both buoyant plumes and local currents energize turbulent exchanges that control ice melt. Because of challenges in making centimeter‐scale measurements at glaciers, these dynamics at near‐vertical ice‐ocean boundaries are poorly constrained. Here we present the first observations from instruments robotically bolted to an underwater ice face, and use these to elucidate the interplay between buoyancy and externally forced currents in meltwater plumes. Our observations captured two limiting cases of the flow. When external currents are weak, meltwater buoyancy energizes the turbulence and dominates the near‐boundary stress. When external currents strengthen, the plume diffuses far from the boundary and the associated turbulence decreases. As a result, even relatively weak buoyant melt plumes are as effective as moderate shear flows in delivering heat to the ice. These are the first in‐situ observations to demonstrate how buoyant melt plumes energize near‐boundary turbulence, and why their dynamics are critical in predicting ice melt.

Mode Coupling Due to an Underwater Ice Keel in a Broad Frequency Band

Mode Coupling Due to an Underwater Ice Keel in a Broad Frequency Band

Mode Coupling Due to an Underwater Ice Keel in a Broad Frequency Band

Numerical simulation is used to study the possibility of remote acoustic monitoring of underwater keels in ice-covered shallow-water waveguides. A statistically average hummock for the Arctic region is considered, with a keel draft of 8 m, located in a waveguide with a depth of 40 m. It is assumed that the ridge of the hummock is perpendicular to the acoustic track, the length of which is 10 km. A point broadband source and a vertical receiving array are used, which are necessary for extracting the mode amplitudes. It is shown that mode coupling due to the keel manifests itself quite distinctly in modulation of the mode amplitudes in a broad frequency band. A methodology for analyzing this modulation by constructing cepstrograms (spectrograms from the spectrum) is proposed. The cepstrograms reveal dispersion curves corresponding to pairs of coupled modes. Then, from the location of the dispersion curves on the cepstrogram, it is possible to estimate the location of the keel on the track.

Gas dynamics within landfast sea ice of an Arctic fjord (NE Greenland) during the spring–summer transition

Sea ice is an active component of the Earth’s climate system, interacting with both the atmosphere and the ocean. Arctic sea ice is commonly covered by melt ponds during late spring and summer, strongly affecting sea ice physical and optical properties. How melt pond formation affects sea ice gas dynamics and exchanges between sea ice and the atmosphere, with potential feedbacks on climate, is not well known. Here we measured concentrations of N2, O2, and Ar, total alkalinity, and dissolved inorganic carbon within sea ice of Young Sound, NE Greenland, to examine how melt pond formation and meltwater drainage through the ice affect its physical properties and gas composition, including impacts on CO2 exchange with the atmosphere. Sea ice gas composition was controlled mainly by physical processes, with most of the gas initially in gaseous form in the upper ice layer. A minor contribution from biological processes was associated with positive estimates of net community production (up to 2.6 µmol Lice−1 d−1), indicating that the ice was net autotrophic. As the sea ice warmed, the upper ice gas concentrations decreased, suggesting a release of gas bubbles to the atmosphere. However, as melt ponds formed, the ice surface became strongly depleted in gases. Due to melt pond development, meltwater permeated through the ice, resulting in the formation of an underwater ice layer also depleted in gases. Sea ice, including brine, slush, and melt ponds, was undersaturated in CO2 compared to the atmosphere, supporting an uptake of up to −4.26 mmol m−2 d−1 of atmospheric CO2. As melt pond formation progressed, however, this uptake weakened in the strongly altered remaining ice surface (the “white ice”), averaging −0.04 mmol m−2 d−1. This study reveals the importance of melt pond formation and dynamics for sea ice gas composition.

Underwater ice adaptive mapping and reconstruction using autonomous underwater vehicles

The undersides of floating ice shelves and sea ice in the Antarctic and Arctic are among the least accessible environments on Earth. The interactions between ice shelves, sea ice, and the ocean are of considerable scientific interest. In order to fully understand the complex picture of sea ice, and not just its surface, it is quite necessary to map the underside to comprehend the full context of its growth and decay patterns. Autonomous Underwater Vehicles (AUVs) are rapidly becoming the desired platform of choice for mapping the underside of sea ice to provide high-resolution 3D views of sea ice topography. To increase the efficiency and accuracy of AUV sampling behaviors is significant for the under-ice observation mission given its limited endurance. In this paper, we present a low-cost underwater ice mapping framework for small-sized AUVs using adaptive sampling and map reconstruction methods. A small-sized AUV is cost-effective and convenient for operation in polar regions; however, due to its limited loading capacity and energy, it is more applicable for the vehicle to carry single-beam sonar for ice bottom mapping but not multi-beam. Thus, the essential issue in this application is how to obtain the key information of ice topography and how to reconstruct the map of ice draft (namely underwater ice thickness) with AUV sparse mapping swathes. To address this, we propose a graphics-based adaptive mapping method to densify the measuring of ice bottom surface with ‘noticeable’ variations; moreover, we also present a sparse approximation method for ice draft map reconstruction using the sparse mapping swathes from a single-beam sonar. Our efforts are to introduce an effective and efficient approach for underwater ice mapping using low-cost small-sized AUVs. Our proposed adaptive mapping and reconstruction methods are validated in the under-ice scenario created using the field data.

Prevention of Water Intake Blockage by Ice during Supercooling Events

Blockage of water intakes by underwater ice formation during supercooling events is a widespread and common problem in northern regions during winter. In this context, underwater ice formation means deposition of frazil ice and growth of platelet ice. Blockage happens when underwater ice forms on the structural components of the intakes, particularly the intake trash racks, decreasing the area of the intake available for flow. This article evaluates potential solutions for preventing blockage. The solutions are collected into four broad categories: avoidance, prevention, mitigation, and remediation. Avoidance locates the intake so that it is never exposed to supercooled water. Avoidance is not possible in rivers and streams and requires depths in lakes and reservoirs that are not reachable for most intakes. Prevention stops supercooled water from entering the intake. The use of heat to warm the intake flow so that it is not supercooled is the most reliable way of preventing intake blockage by underwater ice. The formation of stable ice covers is a reliable means of preventing blockage events but cannot entirely eliminate them. Mitigation modifies the intake, or its operation, to prevent blockage. Ice adhesion to trash rack bars can be reliably prevented by maintaining the bar surface at a temperature greater than 0°C. Other approaches to mitigation including reducing intake flow, modifying the trash rack design, using coatings or alternative materials, or insulating portions of trash rack bars are not reliable for preventing blockage. Remediation actively removes underwater ice from the intake components while the intake is in operation. Mechanical or manual raking of the intake trash racks to remove deposited frazil ice can be a reliable means of preventing blockage. In addition, a strategy, management, addresses intake operation when practical measures for blockage prevention are not available. Management accommodates periodic blockages into the operation of facilities through detection, damage prevention, and quick and efficient restarts.

Underwater ice boosts production of the world ocean's densest waters.

Waters cooled below freezing point adjacent to Cape Darnley, Antarctica generate subsurface ice and produce dense waters that flood the global ocean abyss.

Dominant frazil ice production in the Cape Darnley polynya leading to Antarctic Bottom Water formation.

Antarctic Bottom Water (AABW) occupies the abyssal layer of the world ocean and contributes to the global overturning circulation. It originates from dense shelf water, which forms from brine rejection during sea ice production. An important region of AABW formation has been identified off the Cape Darnley polynya. However, it remains unclear why and how high ice production leads to AABW formation. Using moored acoustic measurements and a satellite microwave algorithm, we reveal that underwater frazil ice dominates in the polynya. This underwater ice formation prevents heat-insulating surface-cover ice forming, thereby enabling efficient ice production. The high ice production in the nearshore and longer residence times create high-salinity source water for the AABW. Underwater frazil ice occurs as long as strong winds continue and occasionally penetrates depths of at least 80 m. Deep-penetrating frazil ice is particularly prominent in this polynya, while it also occurs in other Antarctic coastal polynyas.

Cryofouling avoidance in the Antarctic scallop Adamussium colbecki

The presence of supercooled water in polar regions causes anchor ice to grow on submerged objects, generating costly problems for engineered materials and life-endangering risks for benthic communities. The factors driving underwater ice accretion are poorly understood, and passive prevention mechanisms remain unknown. Here we report that the Antarctic scallop Adamussium colbecki appears to remain ice-free in shallow Antarctic marine environments where underwater ice growth is prevalent. In contrast, scallops colonized by bush sponges in the same microhabitat grow ice and are removed from the population. Characterization of the Antarctic scallop shells revealed a hierarchical micro-ridge structure with sub-micron nano-ridges which promotes directed icing. This concentrates the formation of ice on the growth rings while leaving the regions in between free of ice, and appears to reduce ice-to-shell adhesion when compared to temperate species that do not possess highly ordered surface structures. The ability to control the formation of ice may enable passive underwater anti-icing protection, with the removal of ice possibly facilitated by ocean currents or scallop movements. We term this behavior cryofouling avoidance. We posit that the evolution of natural anti-icing structures is a key trait for the survival of Antarctic scallops in anchor ice zones.

Supplementing Remote Sensing of Ice: Deep Learning-Based Image Segmentation System for Automatic Detection and Localization of Sea-ice Formations From Close-Range Optical Images

This paper presents a three-stage approach for the automated analysis of close-range optical images containing ice objects. The proposed system is based on an ensemble of deep learning models and conditional random field postprocessing. The following surface ice formations were considered: Icebergs, Deformed ice, Level ice, Broken ice, Ice floes, Floebergs, Floebits, Pancake ice, and Brash ice. Additionally, five non-surface ice categories were considered: Sky, Open water, Shore, Underwater ice, and Melt ponds. To find input parameters for the approach, the performance of 12 different neural network architectures was explored and evaluated using a 5-fold cross-validation scheme. The best performance was achieved using an ensemble of models having pyramid pooling layers (PSPNet, PSPDenseNet, DeepLabV3+, and UPerNet) and convolutional conditional random field postprocessing with a mean intersection over union score of 0.799, and this outperformed the best single-model approach. The results of this study show that when per-class performance was considered, the Sky was the easiest class to predict, followed by Deformed ice and Open water. Melt pond was the most challenging class to predict. Furthermore, we have extensively explored the strengths and weaknesses of our approach and, in the process, discovered the types of scenes that pose a more significant challenge to the underlying neural networks. When coupled with optical sensors and AIS, the proposed approach can serve as a supplementary source of large-scale `ground truth' data for validation of satellite-based sea-ice products. We have provided an implementation of the approach at https://github.com/panchinabil/sea_ice_segmentation.

Исследование воздействия подводного взрыва на ледовый покров

The paper presents the results of studies of the features of deformation and destruction of the ice cover affected by a close underwater explosion, as well as by horizontally installed cylindrical shells under the combined action of the explosion and hydrostatic pressure. The research is based on the results of computer simulation of the processes of underwater explosion and ice cover deformation. It is shown that the second pulsation of the bubble exerts a controlling influence on the nature and parameters of the deformation and destruction of the ice cover under the combined action of a close underwater explosion and a large hydrostatic pressure on the shell. The dependence of the ice explosion resistance on the depth and power of the charge is determined. The influence of the main physical parameters of ice on the explosion resistance is revealed. The results of the research can be used for creating structures effectively resisting the effects of a close underwater explosion.

Underwater Ice Terrace Observed at the Front of Glaciar Grey, a Freshwater Calving Glacier in Patagonia

AbstractUnderwater ice geometry at the front of calving glaciers provides crucial information for calving and underwater melting. In this study, we present ice geometry captured by operating a side‐scanning sonar near the front of Glaciar Grey, a freshwater calving glacier in Patagonia. The observations revealed ice projecting into the lake with a substantially different structure from that of known tidewater glaciers. Terrace‐like ice structures were found at several tens of meters below the water surface and extended up to 100 m from the aerial ice front. The structure depicted by the sonar was confirmed when the ice front was exposed by flotation during a major calving event. We infer that buoyant force acting on the submerged ice terrace acted as a driver of the calving event. Our study demonstrates the importance of the underwater ice geometry, which affects sizable calving at the front of freshwater calving glaciers.

The role of ice dynamics in shaping vegetation in flowing waters

Ice dynamics is an important factor affecting vegetation in high-altitude and high-latitude streams and rivers. During the last few decades, knowledge about ice in streams and rivers has increased significantly and a respectable body of literature is now available. Here we review the literature on how ice dynamics influence riparian and aquatic vegetation. Traditionally, plant ecologists have focused their studies on the summer period, largely ignoring the fact that processes during winter also impact vegetation dynamics. For example, the freeze-up period in early winter may result in extensive formation of underwater ice that can restructure the channel, obstruct flow, and cause flooding and thus formation of more ice. In midwinter, slow-flowing reaches develop a surface-ice cover that accumulates snow, protecting habitats under the ice from formation of underwater ice but also reducing underwater light, thus suppressing photosynthesis. Towards the end of winter, ice breaks up and moves downstream. During this transport, ice floes can jam up and cause floods and major erosion. The magnitudes of the floods and their erosive power mainly depend on the size of the watercourse, also resulting in different degrees of disturbance to the vegetation. Vegetation responds both physically and physiologically to ice dynamics. Physical action involves the erosive force of moving ice and damage caused by ground frost, whereas physiological effects - mostly cell damage - happen as a result of plants freezing into the ice. On a community level, large magnitudes of ice dynamics seem to favour species richness, but can be detrimental for individual plants. Human impacts, such as flow regulation, channelisation, agriculturalisation and water pollution have modified ice dynamics; further changes are expected as a result of current and predicted future climate change. Human impacts and climate change can both favour and disfavour riverine vegetation dynamics. Restoration of streams and rivers may mitigate some effects of anticipated climate change on ice and vegetation dynamics by, for example, slowing down flows and increasing water depth, thus reducing the potential for massive formation of underwater ice.

Cross-borehole resistivity tomography of Arctic and Antarctic sea ice

AbstractAs an inhomogeneous mixture of pure ice, brine, air and solid salts the physical properties of sea ice depend on its highly temperature-dependent microstructure. Understanding the microstructure and the way it responds to variations in temperature and salinity is crucial in developing an improved understanding of the interaction between sea ice and the environment. However, measurements monitoring the internal structure of sea ice are difficult to obtain without disturbing its natural state. We have recently developed an application of cross-borehole d.c. resistivity tomography to make in situ measurements that resolve the anisotropic resistivity structure of first-year sea ice. We present results from measurements made in 2008 off Barrow, Alaska, and in 2009 off Ross Island, Antarctica. the sea ice in these two regions forms in different environments: at Barrow, relatively quiescent conditions typically lead to a predominance of columnar ice, while more turbulent conditions and underwater ice formation in McMurdo Sound tend to produce a larger component of frazil or platelet ice. Interpretation of the resistivity measurements carried out in association with temperature and salinity data collected simultaneously allows both observation of the temporal evolution of the ice structure and, in the case of the Antarctic measurements, the identification of different ice types.

To the theory of underwater ice evolution, or nonlinear dynamics of “false bottoms”

We present a mathematical model describing evolution of false bottoms often met between an under-ice melt pond and the underlying ocean during summer. The model treats a false bottom as the region of mixed phase (mushy layer) whose coordinates depend on time and determine the phase transition area. As the heat and the salt fluxes in the ocean are strongly influenced by turbulence and the ice meltwater accumulating underneath the ice cover is practically fresh, we use modified boundary conditions for heat and mass fluxes at the interfaces of phase transition. Explicit analytical solutions (thickness of false bottom and growth rates of its boundaries, temperature and salinity distributions, solid phase fraction and ocean-to-ice heat flux) of the nonlinear model under consideration are found. Model predictions are in good agreement with existing experimental data and physical concepts of phenomena under study.

Tracer studies of pathways and rates of meltwater transport through Arctic summer sea ice

At the Surface Heat Budget of the Arctic Ocean (SHEBA) program's field site in the northern Chukchi Sea, snow and ice meltwater flow was found to have a strong impact on the heat and mass balance of sea ice during the summer of 1998. Pathways and rates of meltwater transport were derived from tracer studies (H218O, 7Be, and release of fluorescent dyes), complemented by in situ sea‐ice permeability measurements. It was shown that the balance between meltwater supply at the surface (averaging between 3.5 and 10.5 mm d−1) and ice permeability (between <10−11 and >10−9 m2) determines the retention and pooling of meltwater, which in turn controls ice albedo. We found that the seasonal evolution of first‐year and multiyear ice permeability and surface morphology determine four distinct stages of melt. At the start of the ablation season (stage 1), ponding is widespread and lateral melt flow dominates. Several tens of cubic meters of meltwater per day were found to drain hundreds to thousands of square meters of ice through flaws and permeable zones. Significant formation of underwater ice, composed between <30 and >50% of meteoric water, formed at these drainage sites. Complete removal of snow cover, increase in ice permeability, and reductions in hydraulic gradients driving fluid flow mark stage 2, concurrent with a reduction in pond coverage and albedo. During stage 3, maximum permeabilities were measured, with surface meltwater penetrating to 1 m depth in the ice and convective overturning and desalination found to dominate the lower layers of first‐year and thin multiyear ice. Enhanced fluid flow into flaws and permeable zones was observed to promote ice floe breakup and disintegration, concurrent with increases in pond salinities and 7Be. Advective heat flows of several tens of watts per square meter were derived, promoting widening of ponds and increases in pond coverage. Stage 4 corresponds to freeze‐up. Roughly 40% of the total surface melt was retained by the ice cover within the ice matrix as well as in surface and under‐ice ponds (with a total net retention of 15%). Based on this work, areas of improvement for fully prognostic simulations of ice albedo are identified, calling for parameterizations of sea‐ice permeability and the integration of ice topography and refined ablation schemes into atmosphere‐ice‐ocean models.

AN IMPROVED CONTINUOUS LIQUID-ICING SYSTEM BASED ON SUBMERGED MIXING OF WATER AND ICE

In industry, the water-ice slurry used for liquid-icing agricultural produce is prepared in batches. Large electric motors are used to operate and maintain the productivity of these ice-water mixing systems. To overcome the disadvantages of the present commercial systems, the concept of continuous-flow ice slurry with underwater ice and water mixing was developed. A prototype was built and tested. These tests showed that the prototype can provide an ice flow rate of 0.91 kg/s. At this flow rate, the prototype can liquid-ice 180 to 210 boxes of broccoli per hour with a power requirement of 1.15 kW.

The Influence of Ice on Southern Lake Michigan Coastal Erosion

Coastal ice does not protect the coast but enhances erosion by displacing severe winter wave energy from the beach to the shoreface and by entraining and transporting sediment alongshore and offshore. Three aspects of winter ice in Lake Michigan were studied over a 3-year period and found to have an important influence on coastal sediment dynamics and the coastal sediment budget: (1) the influence of coastal ice on shoreface morphology, (2) the transport of littoral sediments by ice, and (3) the formation of anchor and underwater ice as a frequent and important event entraining and transporting sediment. Coastal lake ice includes a belt of mobile brash (ice blocks) and slush and a dynamic nearshore ice complex consisting of an icefoot, a lakeward sequence of wave-generated ice ridges, and intervening ice lagoons. Our studies indicate that the nearshore ice complex contains a sediment load (0.2 - 1.2 t/m of coast) that is roughly equivalent to the average amount of sand eroded from the coastal bluffs and to the amount sand ice-rafted offshore to the deep lake basin each year. Up to 0.28 t/m of coast can be entrained by ice in a single anchor-ice event, and separate events occurred on 15 days in January 1991. The brash/slush belt is the most important system component responsible for ice-induced sediment transport. Estimates of longshore ice drift, ice volume, and ice-borne sediment load suggest that 0.36 to 4.14 × 10 3 t/d are transported alongshore.

Textural characteristics and impurity content of meteoric and marine ice in the Ronne Ice Shelf, Antarctica

AbstractThe texture and physical properties of an ice core, recovered to 215 m depth from the Ronne Ice Shelf, Antarctica, have been studied with regard to formation and transformation of the ice. At a depth of 152.8 m, a sharp discontinuity marks the transition between meteoric ice accumulated from above and marine ice accreted from below, as testified by electrolytical conductivity and stable-isotope measurements as well as geophysical field surveys. Automated image analysis of thin sections indicates that the decrease in grain-boundary density and the increase in grain cross-sectional area with depth is commensurate with though not necessarily caused by thermodynamically driven grain growth down to 120 m depth, corresponding to a vertical strain of roughly 65% as computed with a simple temperature-history, particle-path model. The observed increase of grain-boundary density (i.e. a decrease of grain-size) with age in the marine ice is in part explained by the thermal history of this layer. Sediment inclusions at the top of the marine-ice layer affect the observed grain-boundary density profile by inhibiting grain growth and dynamic recrystallization. This may allow some conclusions on the role of temperature, particulate inclusions, stress and strain rate in controlling the grain-size evolution of deforming ice, supplementing earlier laboratory experiments conducted at much shorter time-scales. Salinities (0.026%), brine volumes (0.09–0.2%) and solid-salt concentrations have been computed from electrolytical conductivity measurements (mean of 51.0 × 10−6 S cm−1) for the marine ice. An assessment of salt incorporation and desalination rates shows that these low salinities can at present only be explained by a unique densification mechanism of under-water ice crystals at the base of the ice shelf.

Textural characteristics and impurity content of meteoric and marine ice in the Ronne Ice Shelf, Antarctica

AbstractThe texture and physical properties of an ice core, recovered to 215 m depth from the Ronne Ice Shelf, Antarctica, have been studied with regard to formation and transformation of the ice. At a depth of 152.8 m, a sharp discontinuity marks the transition between meteoric ice accumulated from above and marine ice accreted from below, as testified by electrolytical conductivity and stable-isotope measurements as well as geophysical field surveys. Automated image analysis of thin sections indicates that the decrease in grain-boundary density and the increase in grain cross-sectional area with depth is commensurate with though not necessarily caused by thermodynamically driven grain growth down to 120 m depth, corresponding to a vertical strain of roughly 65% as computed with a simple temperature-history, particle-path model. The observed increase of grain-boundary density (i.e. a decrease of grain-size) with age in the marine ice is in part explained by the thermal history of this layer. Sediment inclusions at the top of the marine-ice layer affect the observed grain-boundary density profile by inhibiting grain growth and dynamic recrystallization. This may allow some conclusions on the role of temperature, particulate inclusions, stress and strain rate in controlling the grain-size evolution of deforming ice, supplementing earlier laboratory experiments conducted at much shorter time-scales. Salinities (0.026%), brine volumes (0.09–0.2%) and solid-salt concentrations have been computed from electrolytical conductivity measurements (mean of 51.0 × 10−6S cm−1) for the marine ice. An assessment of salt incorporation and desalination rates shows that these low salinities can at present only be explained by a unique densification mechanism of under-water ice crystals at the base of the ice shelf.