Ice Pressure Ridges Research Articles

Studies of Ice Processes in the Arctic for the Developing the Forecasting Ice Conditions Models and Methods Necessary for Navigation Support in the North Sea Route Area

The thermodynamic and dynamic processes causing the ice cover formation, growth and dynamics are consid- ered. The significance of studying the dangerous ice phenomena like intensive ice drift, ice pressure and ice ridge formation is shown. The brief description of ice cover evolution model used for the short-range ice forecasts is presented. The multi-year variability of ice cover extent in the Arctic Ocean as a whole and in the Arctic seas in particular is analyzed. The basic principles of dividing the ice conditions into types both in summer and winter are presented. The methods of short-range (up to 5 days) and long-range (up to 30 days) ice forecasts are briefly described. The practical realization of forecasting the type of ice conditions used by the North Sea Route Adminis- tration for providing the permissions for navigation in the NSR area is demonstrated.

The Three‐Dimensional Light Field Within Sea Ice Ridges

AbstractSea ice pressure ridges have been recognized as important locations for both physical and biological processes. Thus, understanding the associated light‐field is crucial, but their complex structure and internal geometry render them hard to study by field methods. To calculate the in‐ and under‐ridge light field, we combined output from an ice mechanical model with a Monte‐Carlo ray tracing simulation. This results in realistic light fields showing that light levels within the ridge itself are significantly higher than under the surrounding level ice. Light guided through ridge cavities and scattering in between ridge blocks also results in a more isotropic ridge‐internal light field. While the true variability of light transmittance through a ridge can only be represented in ray tracing models, we show that simple parameterizations based on ice thickness and macro‐porosity allow accurate estimation of mean light levels available for photosynthesis underneath ridges in field studies and large‐scale models.

A Distributed Snow‐Evolution Model for Sea‐Ice Applications (SnowModel)

AbstractSnow‐depth distributions on sea ice have substantial impacts on winter ice growth and summer ice melt. There are two types of wind‐related snow distributions in this environment: snowdrifts that form around ice pressure ridges; and snow dunes and other snow bedforms that form on relatively level, undeformed ice. A snow‐evolution modeling system (SnowModel) was tested against winter snow observations collected during the Norwegian young sea ICE expedition (N‐ICE2015) north of Svalbard, with an emphasis on reproducing these two types of snow distributions. The SnowModel simulation spanned 1 year, summer 2014 through summer 2015, over a 1.5 km by 1.5 km domain, using a 1 m horizontal grid increment and 3 h time step. Existing SnowModel components, created originally for terrestrial applications, performed energy balance, snow property, snowdrift, and data assimilation calculations in response to prescribed meteorological forcings. A new SnowModel component, SnowDunes, was created to simulate snow‐bedform distributions on level, undeformed ice. Model results reproduced observed snowdrift profiles around pressure ridges and snow‐depth distributions over level, undeformed ice, resulting in physically realistic snow heterogeneity and property information. We conclude that the SnowModel toolkit contains the components required to simulate most processes driving the seasonal distribution of snow on sea ice. SnowModel can evolve snow on sea ice over local to pan‐Arctic areas, using grid increments ranging from 1 m to tens of km, and time increments of subhourly to daily.

Salt marsh flora and vegetation of the Russian Arctic coasts

The flora of open coasts and the estuaries of rivers is an important element of the Arctic flora and represents the littoral halophytic floristic complex. The salt marsh flora includes 113 species of vascular plants (12% of the total amount of Arctic flora), belonging to 62 families. Due to geographical conditions, the partial floras of coastal wetlands of the Russian Arctic have similar taxonomic and typological structure. In the geographical structure of flora-coenotic complex, the Arctic circumpolar species dominate. The Arctic coastlines are subjected to frequent disturbances associated with frost action, storms and ice pressure ridges that affect species richness and the ability of human populations to exploit coastal resources successfully. The dynamic changes of salt-marsh plant communities are site-specific: 1) in the initial stages, vegetation development mostly depends on the physical-chemical substrate properties and tidal action, 2) the spatial-temporal processes of successional change over a long time result in the environment development and changes in edaphic conditions. The time scale of these changes brought about by disturbances is biologically important as there must be sufficient time to allow genetic adaptation in plant and animal populations.

Morphology of sea ice pressure ridges in the northwestern Weddell Sea in winter

To investigate the morphology and distribution of pressure ridges in the northwestern Weddell Sea, ice surface elevation profiles were measured by a helicopter‐borne laser altimeter during Winter Weddell Outflow Study with the German R/V Polarstern in 2006. An optimal cutoff height of 0.62 m, derived from the best fits between the measured and theoretical ridge height and spacing distributions, was first used to separate pressure ridges from other sea ice surface undulations. It was found that the measured ridge height distribution was well modeled by a negative exponential function, and the ridge spacing distribution by a lognormal function. Next, based on the ridging intensity Ri (the ratio of mean ridge sail height to mean spacing), all profiles were clustered into three regimes by an improved k‐means clustering algorithm: Ri ≤ 0.01, 0.01 < Ri ≤ 0.026, and Ri > 0.026 (denoted as C1, C2, and C3 respectively). Mean (and standard deviation) of sail height was 0.99 (±0.07) m in Regime C1, 1.12 (±0.06) m in C2, and 1.17 (±0.04) m in C3, respectively, while the mean spacings (and standard deviations) were 232 (±240) m, 54 (±20) m, and 31 (±5.6) m. These three ice regimes coincided closely with distinct sea ice regions identified in a satellite radar image, where C1 corresponded to the broken ice in the marginal ice zone and level ice formed in the Larsen Polynya, C2 corresponded to the deformed first‐ and second‐year ice formed by dynamic action in the center of the study region, and C3 corresponded to heavily deformed ice in the outflowing branch of the Weddell Gyre. The results of our analysis showed that the relationship between the mean ridge height and frequency was well modeled by a logarithmic function with a correlation coefficient of 0.8, although such correlation was weaker when considering each regime individually. The measured ridge height and frequency were both greater than those reported by others for the Ross Sea. Compared with reported values for other parts of the Antarctic, the present ridge heights were greater, but the ridge frequencies and ridging intensities were smaller than the most extreme of them. Meanwhile, average thickness of ridged ice in our study region was significantly larger than that of the Coastal Ross Sea showing the importance of deformation and ice age for ice conditions in the northwestern Weddell Sea.

Model sensitivity analysis of scattering-induced attenuation of ice-coupled waves

The sensitivity of the rate of exponential decay of wave energy through the ice-covered oceans is investigated using a two-dimensional (one horizontal and one depth) linear model. Attenuation in the model results from multiple wave scattering caused by features (irregularities) in the ice cover. The focus of the study is the assimilation of ocean wave/sea ice interactivity—experienced via the attenuation in the model, into an operational ice/ocean forecasting paradigm. Attenuation coefficients are considered, which define the rate of exponential decay as functions of the properties of the ice cover and the incident wave field. It is shown first that wave scattering can be highly sensitive to the values of Young’s modulus that are typical of natural sea ice, but that the difference between the values for first-year and multi-year ice is small. Three common ice cover features, namely floes, cracks and pressure ridges, are then examined and compared. Regimes in which particular irregularities are dominant are identified and approximations are derived for the attenuation coefficients produced by each feature. Attenuation produced by rough ice is considered as well, but it is found to be insignificant compared to that due to the three prototype irregularities chosen.

3D EM modelling of Antarctic sea ice pressure ridges

The use of airborne electromagnetic (AEM) surveys to measure Antarctic sea ice thickness is being investigated as a regional mapping tool to aid global climate studies. Undeformed sea ice floes are modelled as 1D structures. However, sea ice pressure ridge sails (in air) and keels (undersea) form convenient 2D and 3D targets. In order to use AEM techniques to study the distribution of ice thickness, it is first necessary to test if realistic sea ice structures can be modelled electromagnetically. Pressure ridge structures from drillhole sampling can in some cases be constructed from simple block models. Finite element and integral equation 3D EM modeling programs can then be applied to these structures to test for agreement, and to predict the AEM response, including topography (sails). EM modelling of frequency domain systems shows that good agreement is obtained at certain frequencies and that a vertical coaxial (VCX) transmitter?receiver coil configuration laterally resolves the ice keel better than a horizontal coplanar (HCP) configuration. Cross-sectional dimensions of the sails and keels are relatively small and mesh design is critical in order to avoid discretisation errors. Software and hardware constraints may limit successful EM modeling of multiple keels that combine sub-metre structures and coarser structures. For a given mesh, discretisation errors may lead to noisy EM response profiles depending on the frequency, coil geometry, and component (in-phase or quadrature). Adaptive mesh structures may be required to minimise discretisation errors.

BASIC STUDY ON INTERACTION BEWEEN SEA ICE AND SEA BED

Ice Scour (Ice Gouging) is a phenomenon in which sea ice (pressure ridge, ice keel) attached to the sea bottom in a shallow sea area scrapes the sea bottom while it is pushed by wind and water current from offshore ice field to shallow sea area. There have been reported instances of damage to transatlantic submarine telecommunication, water intake pipeline at Great Slave Lake etc. So, the problem of Ice Scour by sea ice and ridge keels is of concern in the planning and design ofseabed installation.In this study we describe the mechanism of Ice Scour andobtain basic knowledge necessary to take preventive measures in future against damage by sea ice.

Continuous paleoclimate record recovered for last 5 million years

From January to March 1996, an ice‐based drilling platform (Figure 1) was positioned in 321 m of water above a submerged topographic high known as the Academician Ridge of Lake Baikal, south‐central Siberia (Figure 2). The Russian Nedra drilling team expertly used this system to recover the first sediment cores from this region to span the last 5 m.y. before present (Ma). This operation was complicated and dangerous: there were constantly shifting blocks of ice nearly 1 m thick, the location was surrounded by wilderness areas nearly 400 km from the nearest population center (Irkutsk), and supplies and personnel had to travel 90 km over the ice pressure ridges in 4‐wheel motorcycles and small vehicles.

Passive microwave signatures of simulated pancake ice and young pressure ridges

This paper describes surface based passive microwave observations of simulated pancake ice and of a first year pressure ridge. The observed emissivity spectra are quite similar to those observed on...

Editor's Note

124Victorian Review MacLaren (Alberta) turned our focus simultaneouslyto the past and northward, prompting yet more understanding of the Victorian artist's, explorer's, and publisher's methods of bringing new areas to the British pubUc by presenting them in the guise of traditional forms. Just as ships' journals attest to the attempt of English sailors (especially officers) to make English prospects (such as a cricket ground) in the High Arctic, the sketches by ships' artists offer the bizarre comedy of ice pressure ridges transformed to hedgerows and deciduous trees appearing in landscapes hundreds of mUes above the tree line. Our Conference Convenors, JuUet McMaster and Glennis Stephenson, complemented this intellectual fare with sumptuous snacks; a post-conference party at the McMasters put the ideal finishing touch to the Nineteenth Annual Conference, October 11-13, 1990. Dale Wilkie University of Alberta EDITOR'S NOTE: We wanted to end this summary with something that would capture the essence of the other side of VSAWC conferences, the social side. Here then, to remind you of a most memorable moment from Friday evening's banquet and entertainment, is a transcript of L. M. Findla/s introduction to his stirring reading of WiUiam McGonagall's "Women's Suffrage." Before starting to read, you may want, to help recall the moment exactly, to indulge in a few too many glasses of port or Irish Mist. Situating the Bard After I had hesitantly agreed on the telephone, Juliet McMaster sent me a text to read for you this evening. It was a text both familiar and strange, so, being me, I had of course to situate it theoretically before it could become a Uttle more my own. Here is the result of that act of situation, an instance of academic weaseling if you will. I am charged with giving a reading from a bard whose time has come, the unjustly marginalized WiUiam McGonagall, that dour, overdetermined figure ofthe pedestrian muse at Queen Victoria's gates. McGonagall is an aufhor-fuction hitherto too readily dismissed, invisible from theory's panopticon, unreadable by even the most voracious textual fetishist, and thought of more generally as the loon who gave doggerel a bad name. But we know better, don't we? We can see and savour not only the fhematized deconstruction of "The Tay Bridge Disaster," but, more discursively in his oeuvre, a shrewdly ironized post-Romanticism whose dominant symbols are not the Mirror and the Lamp but the Sphincter and the Cramp, the non-ludic re-corporealizing of the transcendental in the commode of production. McGonagall put the pith back in epithtemology, displacing the floating by the sunken signifier, the phonocentric and phalUogocentric by the trope of motivated ineptitude. Sit back and enjoy, then, the suave brutality of his prosody, the ideological arhythmia of the foUowing assault on state apparatuses, the aporetic convergence of the cliche and Kierkegaardian repetition. After I have finished reading, you may wish to reconsider the implications of that familiar expression, "A figure of fun. [There foUowed a reading of "Women's Suffrage"] L. M. FINDLAY ...

Ice island detection and characterization with airborne synthetic aperture radar

A 1∶300,000 scale airborne synthetic aperture radar (SAR) image of an area of the Arctic Ocean adjacent to the Queen Elizabeth Islands, Canadian High Arctic, is examined to determine the number and characteristics of ice islands in the image and to assess the capability of airborne and satellite SAR to detect ice islands. Twelve ice islands have been identified, and their dimensions range from as large as 5.7 km by 8.7 km to as small as 0.15 km by 0.25 km. A significant SAR characteristic of the shelf ice portions of ice islands is a return with a ribbed texture of alternating lighter and darker grey tones resulting from the undulating shelf ice surfaces of the ice islands. The appearance of the ribbed texture varies according to the ice islands' orientation relative to the illumination direction and consequently the incidence angle. Some ice islands also include extensive areas of textureless dark tone attached to the shelf ice. The weak returns correspond to (1) multiyear landfast sea ice that was attached to the front of the Ward Hunt Ice Shelf at the time of calving and which has remained attached since then and (2) multiyear pack ice that has become attached and consolidated since the calving, indicating that ice islands can increase their area and mass significantly as they drift. Other SAR characteristics include straight, bright returns along the edges arising from sea ice pressure ridges or shelf ice cliffs. Other physical characteristics of ice islands that make them identifiable in SAR images include their greater size and shapes longer, thinner, and more angular than those of surrounding pack ice floes. It is evident that ice islands are easily discernible in SAR images and for the future SAR represents a promising technique to obtain a census of ice islands in the Arctic Ocean. However, any SAR‐based census probably will be conservative because ice islands smaller than 300–400 m across are likely to remain undetected, particularly in areas of heavy ice ridging which produces strong SAR clutter.

Measurements of ridge sails in the Beaufort Sea

Ice pressure ridges in the southern Beaufort Sea near Tuktoyaktuk were surveyed in April 1986. Sail cross-section profiles and ice-block dimensions of ridges of extreme heights were measured at several locations along the outer edge of the landfast ice. Statistical distributions of sail heights as well as correlations between sail dimensions and between ice block dimensions are obtained. Geographical distribution of sail dimensions and longitudinal changes along individual ridges are examined. Key words: ridges, landfast ice, sea ice, ridge sails, ridge statistics, Beaufort Sea.

Model of Ice Rubble Pileup

A model of floating ice pressure ridges is developed. A two‐dimensional symmetric wedge is assumed to represent the sail (or keel) of a ridge. The stochastic model of stress transfer in particulate media and the equilibrium equations are used to determine the stress distribution. The kinematics of the problem are not considered in the analysis. The Mohr‐Coulomb criterion is used to determine failure zones and consequently the limiting height and depth of the ridge. The model predicts forces in the ice cover associated with limiting ridge height and depth and gives some information about ridge geometry. The results are compared to other computation methods. Force predictions appear to be of the same order observed when floating ice impinges on wide structures.

Nearfield noise measurements from an Arctic pressure ridge

This paper presents initial analysis results of ambient noise measurements from an active ice pressure ridge over a 3-day period in April 1979. The site was a research ice camp 180 miles from the pole in the Eurasian Basin of the Arctic Ocean. The ridge was instrumented with calibrated hydrophones paired in both the horizontal and vertical directions. Their distance from the ridge was about 100 m and their outputs were tape recorded. Dimensional surveys of the active portions of the ridge were made at the surface. Source level linear density is deduced from ambient noise measurements near the pressure ridge by assuming the ridge to be a line source of spatially incoherent point sources. Measured Arctic transmission loss data are used to deduce an active pressure ridge average separation compatable with previously measured omnidirectional ambient noise data statistics for the month of April. The effects of surface/image interference are present in the data and allow a preliminary estimate of acoustic source depth of between 14–18 m. The ridge length was approximately 500 m and was formed when a 1 m-thick refrozen lead was pushed on top of a thicker 4-m ice floe. As such, this ridge was, most likely only one ‘‘subridge’’ along the length of the boundaries of the two interacting floes. Recent SEASAT SAR data from October 1978 have shown that ice pans (defined as groups of separate ice floes that move together) can vary from 10 to 100 km in linear dimension and, unless pan size changes significantly from October to April, extremely long ridges (composed of smaller discrete ridges such as the one analyzed in this study) may exist between pressured boundaries of adjacent pans. A uniform spacing of ridges was assumed for noise model calculations and, with an active ridge spacing of 37 km, model noise level estimates and measured 50 percentile noise levels of April were in good agreement. An average ridge was assumed to be 2 km in length consisting of two active 500-m subridges. It is not known whether this ridge was typical in level, length, etc., since these were the first-known quantitative acoustical measurements of ambient noise from a nearby pressure ridge.

Angular dependence of under ice reflectivity in the marginal ice zone (MIZ)

Acoustic reflectivity measurements from sea ice in the MIZ were taken during MIZEX‐84. Signals from explosive charges (MK‐61 and ‐82 SUS) received on 12 hydrophones of a 313‐m vertical array were processed to separate single bounce ice reflections from direct path and bottom reflected arrivals by replica deconvolution. Ice reflection loss was computed from the ratio of reflected energy to direct path energy after correction for spreading loss differences between the two paths. Signals from different source ranges and receiver depths were collected on the basis of their specular reflection grazing angles spanning the interval 10° to 30°. Data points with estimated standard deviation of reflectivity greater than 0.2 (based on noise estimates) were excluded. The resulting reflectivity versus grazing angle curves at 64, 96, and 128 Hz displayed high variance presumably due to scattering from a single under ice pressure ridge within the Fresnel zone. With angular smoothing the curves showed small angular dependence and losses on the order of 1.5 dB. Comparison of results with model computations will be discussed.

Structure, Salinity and Density of Multi-Year Sea Ice Pressure Ridges

Data are presented on the variation of ice structure, salinity, and density in multi-year pressure ridges from the Beaufort Sea. Two continuous multi-year pressure ridge cores are examined as well as ice sample data from numerous other pressure ridges. The results suggest that the large scale properties of multi-year pressure ridges are not isotropic, and that the use of anisotropic ridge models may result in lower design ridge ice loads.

Detection of sea-ice features using Ka-band radar

Analysis of recorded radar data collected from a mixed field of Arctic ice shows that the Ka-band returns, more so than other frequencies, can be used to delineate targets that pose a threat or impediment to navigation. In particular, it is shown that the Ka-band returns highlight multiyear ice-floes, ice-bergs and first-year ice pressure ridges.

Morphological investigations of first-year sea ice pressure ridge sails

Sea ice pressure ridge sail heights and the dimensions of ice blocks that comprised the sails were measured for 30 ridges in April, 1980. The ridges were located from 30 to 200 km offshore in the Prudhoe Bay, Alaska region. Sail height was found to be a function of the thickness of the ice in the ridge. A reasonable relationship shows that height is dependent on the square root of block thickness. The data also verify that the ratio of sail height to ice block thickness is much larger for ridges composed of thin ice than for those composed of thick ice. Ridge width and cross-sectional area are also found to be related to block thickness. For the largest blocks in the ridge, block surface area is related to thickness squared, as would be expected from plate deflection theory. Examination of lateral variation of height and width along the ridge shows an expected large variation, particularly with height. No geographic variations of individual pressure ridge morphology were discernible from these data, but a laser profile taken during the study period shows that the mean heights and numbers of ridges decrease as the distance from the coast increases.

Source level measurements of an arctic sea ice pressure ridge

Ice pressure ridge activity occurred over a three‐day period in the immediate vicinity of a research ice camp 180 miles from the pole in the Eurasian Basin of the Arctic Ocean in 1979. The ridge was instrumented with both horizontal and vertical calibrated hydrophone pairs at a distance of about 100 m and the acoustic output tape recorded. Dimensional surveys were made atop the ice of the active portions of the ridge. Correlation and spectral analyses were performed which allowed quantitative assessments of source level in the hand 3–1000 Hz. These data, along with previously measured arctic transmission loss, were used to derive a model of pressure ridge area distribution and density by matching previously gathered statistical ambient noise data. The observed ice ridge noise was abundant in fairly long‐lasting tunais as low as 8 Hz attributed to a “slipping clutch” effect. These were the first known quantitative acoustical measurements of a nearby pressure ridge.