bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ice flow around large obstacles as indicated by basal ice exposed at the margin of the Greenland ice sheet
Authors: Knight Peter G. , Sugden David E. , Minty Christopher D. 
Published: September 2017

AbstractSpatial variations in the debris-bearing basal ice layer exposed at the ice-sheet margin in West Greenland reflect the geography of basal melting and ice flow around large obstacles close to the margin. This paper demonstrates the character of the basal ice layer, which comprises fine material incorporated in an interior, subglacial environment and coarser material entrained in an ice-marginal environment. We develop an empirical model of ice flow close to a lobate margin of the ice sheet in which ice convergence and divergence, and limited subglacial melting affect the character and distribution of the basal ice at the margin. There is a tendency for the convergence and divergence to thicken the basal layer in lobate areas and to thin it in inter-lobate areas. Under certain circumstances, basal melting may remove much of the layer from beneath the snouts of larger lobes, thus causing the basal layer to be thickest in an intermediate location.
Observations of flexural waves on the Erebus Ice Tongue, McMurdo Sound, Antarctica, and nearby sea ice
Authors: Squire Vernon A. , Robinson William H. , Meylan Michael , Haskell Timothy G. 
Published: September 2017

AbstractNew strain data relating to flexural oscillations of the Erebus Glacier Tongue (EGT), McMurdo Sound, Antarctica, are presented and are analysed in the frequency domain. The data were collected during November 1989, just 3 months prior to the most recent calving of the ice tongue which occurred in March 1990. A broad-band oscillation centred on 50 s is found in both the strain measurements collected on the EGT and those collected on the sea ice nearby. The oscillation is shown, at least in part, to be propagating with a phase velocity of approximately 65 ms−1 in a direction away from the snout towards the grounding line, rather than being wholly due to a standing-wave pattern in the EGT. A coupling model between the sea ice and the EGT is proposed and is shown to compare reasonably well with the data.
Fracture toughness and crack growth of brackish ice using chevron-notched specimens
Authors: Stehn Lars 
Published: September 2017

AbstractField-test equipment called FIFT (a Field Instrument for Fracture toughness Tests on ice) was used in both field and laboratory fracture-toughness tests on brackish sea ice from the Gulf of Bothnia. An experimental calibration was performed and a compliance expression was then derived for the Short Rod Chevron Notched (SRCN) specimen. Using the SRCN configuration, for which the initial crack growth is shown to be stable, and measured load-point displacements, preliminary crack-growth velocities are found. The obtained estimated crack velocity is, on average,ȧe= 20 ms−1, albeit with a large standard deviation. The results indicate that critical crack (crack-jumping) growth occurs. The apparent fracture toughness,KQ, was found to have a pronounced dependency on porosity in the form of brine volume. The results obtained are derived from a linearly elastic fracture mechanics (LEFM) theory. Consequently, the tests were designed to satisfy small-scale yielding requirements in terms of notch sensitivity and brittleness. The linearity of the load vs crack-opening displacement curves together with a size-effect study, showing that the specimen is notch-sensitive for grain-sizes ranging from 1.6 to nearly 100 mm, indicate that LEFM could be applicable.
Solute Acquisition in Glacial Melt Waters. II Argentière (French Alps): Bulk Melt Waters with Open-System Characteristics
Authors: Thomas A.G. , Raiswell R. 
Published: September 2017

AbstractVariations in dissolved cations, total alkalinity, sulphate, and field pH are recorded for subglacial melt and bulk melt waters (those emerging from the portal) at Argentière (France), in peak and recession flow conditions. Calcium and bicarbonate are the major ions and the bulk melt waters are demonstrated to have acquired solutes by weathering and dissolution in a system open to atmospheric carbon dioxide. Subglacial melt waters have closed-system characteristics, are close to saturation with calcite and quartz, and must be in near-equilibrium with weathered particulates. Recession-flow bulk melt waters are chemically similar to subglacial melt but have open-system characteristics, either due to re-equilibration with the atmosphere for ground-water mixing.
Chemical Models of Solute Acquisition in Glacial Melt Waters
Authors: Raiswell R. 
Published: September 2017

AbstractChemical models for the evolution of bulk melt waters can be constructed by assuming that rock mineral weathering and solute acquisition are controlled by carbonate equilibria. Different open- and closed- system models are defined by variations in the rates of weathering relative to the rate of hydrogen-ion supply by the dissolution and dissociation of CO2, and can be recognized by characteristic pH and ∑+ relationships. The observed and inferred compositions of englacial and subglacial melt suggest that mixing is unlikely to be conservative and that closed-system conditions result where post-mixing weathering reactions occur. The final composition of bulk melt waters is determined by the mixing ratio between englacial and subglacial melt, the extent of post-mixing evolution, and opportunity for mixing with ground waters or re-equilibration with the atmosphere.
Interpretation of the Chemical and Physical Time-Series Retrieved from Sentik Glacier, Ladakh Himalaya, India
Authors: Mayewski Paul A. , Lyons W. Berry , Ahmad N. , Smith Gordon , Pourchet M. 
Published: September 2017

AbstractSpectral analysis of time series of ac. 17 ± 0.3 year core, calibrated for totalßactivity recovered from Sentik Glacier (4908m) Ladakh, Himalaya, yields several recognizable periodicities including subannual, annual, and multi-annual. The time-series, include both chemical data (chloride, sodium, reactive iron, reactive silicate, reactive phosphate, ammonium,δD,δ(18O) and pH) and physical data (density, debris and ice-band locations, and microparticles in size grades 0.50 to 12.70μm). Source areas for chemical species investigated and general air-mass circulation defined from chemical and physical time-series are discussed to demonstrate the potential of such studies in the development of paleometeorological data sets from remote high-alpine glacierized sites such as the Himalaya.
Field pH Determinations in Glacial Melt Waters
Authors: Metcalf Richard C. 
Published: September 2017

AbstractLaboratory pH analyses of glacial melt waters are unrepresentative of in situ values, due primarily to CO2 gas exchange between the sample and the atmosphere, and solute enrichment from chemical reaction with sediment and colloidal particles. A method is presented which enables field pH measurements that are reproducible within ±0.04 pH units to be made in glacial melt waters, using commonly available digital pH meters with combination electrodes.During initial spring snow melt in May 1981 at Gornergletscher, Switzerland, melt waters in the proglacial stream leaving the glacier terminus were oversaturated with respect to atmospheric p(CO2), and rapidly increased pH during CO2 outgassing at in situ temperature and pressure. Summer ice melt from glaciers which are temperate in the ablation zone are usually undersaturated by about ten times with respect to atmospheric p(CO2), and rapidly lower their pH values to achieve equilibrium upon encountering the atmosphere, as observed at Gornergletscher during July and August 1981. Gornergletscher summer proglacial stream waters, sometimes show pH increases from rock weathering, with the rate limited by the transfer rate of CO2 across the air-water interface to drive the weathering reactions. Throughout the year, any water parcel at equilibrium with atmospheric CO2 is generally at an equilibrium pH value, if filtration prohibits solute enrichment. For these reasons, laboratory pH measurements are unacceptable for quantitative studies of melt-water chemistry and should be discontinued.
“Sun Spirals” on Melting Snow
Authors: Jahn Alfred 
Published: September 2017

AbstractThe light oblong elements like blades of grass and wooden sticks resting on the surface of melting snow change their position and arrangement (direction). They turn under the direct influence of the varying angle of the Sun’s rays due to the movement of the Sun. Turning of the elements gives a circular form of arrangement that has been termed ablation “sun spirals”.
Possible Late Palaeozoic Glaciation in the Central Parts of the Yemen Arab Republic
Authors: El-Nakhal Hamed A. 
Published: September 2017

AbstractOccasional outsize clasts, some of which are striated, and laminae bent against the enclosed clasts have been recorded throughout the shales and siltstones forming the lower part of the Kohlan Group in the central parts of the Yemen Arab Republic. Such features are interpreted as an indication of continental glaciation. On stratigraphical grounds, these shales and siltstones are assigned to the Permian.
Optical Properties of Blowing Snow
Authors: Pomeroy J.W. , Male D.H. 
Published: September 2017

AbstractCalculation procedures are developed and results shown for the exact calculation of extinction and meteorological visual range using the blowing-snow mass in the atmosphere and particle radius. Results of the calculations show: (1) For monochromatic radiation, geometrical optics approximations of the extinction efficiency are found to provide results of only moderate accuracy in calculating the extinction of radiation by a single particle. (2) For broad-band radiation, the geometrical optics approximation is sufficiently accurate for many single-particle measurement instruments and applications, except in the infra-red band where Mie theory should be used. (3) For typical blowing-snow particle-size distributions, the shape parameter of the distribution of particle radii and the mean particle radius are very important in broad-band extinction and visual-range modelling. Estimates of blowing-snow quantities from broad-band extinction measurements or visual range from blowing-snow quantities should address the shape and mean value of the snow-particle radius distribution.
On the Albedo of Snow in Antarctica: A Contribution to I.A.G.O.
Authors: Wendler Gerd , Kelley John 
Published: September 2017

AbstractAs part of a larger experiment, detailed albedo measurements were carried out during the austral summer of 1985-86 in the dry-snow zone (1560 m) of Terre Adélie, eastern Antarctica. The following results were found:(1)Mean albedo values were high (around 82.6%). On clear days, the albedo showed some dependency on the solar elevation. The dependency was slight for solar elevations above 12° but became larger with low Sun angles.(2)The albedo was found to be a function of cloud amount and type, increasing with the amount and thickness of clouds. In white-out conditions, very high albedos were found (>90%).(3)The albedo showed a dependency on the type of snow. New snow displayed higher values than older snow, whose crystals had been destroyed by mechanical action.(4)A simple model was developed to assess the influence of sastrugi on the albedo. This model could explain the asymmetric diurnal variation about solar noon of the measured albedo above a sastrugi field.The above four dependencies might explain the considerable discrepancies which can be found in the literature concerning the snow albedo of Antarctica.
Mass Balance Along Two Transects of the West Side of the Greenland Ice Sheet
Authors: Kostecka J.M. , Whillans I.M. 
Published: September 2017

AbstractThe mass balance is computed along the Ohio State University (OSU) transect near the Arctic Circle and along the Expédition Glaciologique Internationale au Groenland (EGIG) line. Measured surface velocities are compared with velocities calculated from up-glacial accumulation rate, flow-line spreading, ice thickness, and the depth variation in horizontal velocity. The depth variation in velocity is calculated using the constitutive relation for ice, calculated temperatures within the glacier, computed shear and longitudinal stresses, and allowance for impurity content and ice-crystal orientation. The resulting mass balance is +0.6 ± 0.14 m a−1 for the OSU transect and 0 ± 0.07 m a−1 along the EGIG line. The errors arise mainly from uncertainties in measured accumulation rate and flow-line spreading, and perhaps in flow-enhancement factors due to ice anisotropy or impurities. The results for the EGIG line differ from prior estimates mainly because earlier works placed greater emphasis on short-term accumulation rates.
A Pressure-sintering Model for the Densification of Polar Firn and Glacier Ice
Authors: Wilkinson D.S. 
Published: September 2017

AbstractA comprehensive multi-mechanism theory of pressure sintering has been applied to the densification of two polar ice sheets. The comparison, which is made using pressure-sintering mechanism maps, indicates that power-law creep is the controlling mechanism between 50% and 98% theoretical density. Lattice diffusion becomes dominant at low porosities. The densification rates predicted by the theory are in good agreement with the data, and suggest that a reasonable estimation of the densification behaviour of a polar ice sheet can be made using the theory, based on information obtained from a relatively shallow core.
A Flow-line Model for Calculating the Surface Profile and the Velocity, Strain-rate, and Stress Fields in an Ice Sheet
Authors: Reeh Niels 
Published: September 2017

AbstractA flow-line model is presented for calculating the surface profile and the velocity, strain-rate, and stress fields in an ice sheet with given base-elevation profile, ice thickness at the dome (divide), flow-law parameters, mass-balance distribution, and convergence/divergence conditions along the flow line. The model, which is based on a “quasi-similarity” hypothesis as regards the horizontal velocity-depth profiles, accounts for changes along the flow line in the depth distributions of temperature, normal stress deviators, and possible enhanced flow of deep ice of Wisconsin origin. A curvilinear coordinate system is applied with horizontal axes along flow lines and surface-elevation contours, respectively. The flow equations are reduced to two differential equations, one for the surface-elevation profile, and the other for a profile function that determines the depth distributions of velocities and strain-rates. The two equations are coupled through a profile parameter that communicates the influence of velocity-profile changes to the surface-profile equation. It is shown that the variation along the flow line of this parameter should also be considered when deriving flow-law parameters from ice-sheet flow-line data. For a symmetric dome, explicit expressions are derived for the depth distributions of the vertical velocity, strain-rates, and stresses. The strain-rate profiles display an inflection about half-way down the ice sheet, and, in the case of isothermal ice, have surface values 2.2 times their depth-averaged values. The depth distribution of the vertical velocity indicates that a relatively thick layer of almost stagnant ice is present at the ice-sheet base below a dome.
A Model of Icicle Growth
Authors: Makkonen Lasse 
Published: September 2017

AbstractA theory of icicle growth is presented. It is shown that icicles elongate as hollow tubes of ice with liquid water trapped inside the tip. A time-dependent computer model based on the theory shows that the growth of an icicle is a complicated process, which is very sensitive to the atmospheric conditions and water flux. The shape and weight of icicles predicted by the model agree well with laboratory data.
The Kinetic Friction of Snow
Authors: Colbeck S.C. 
Published: September 2017

AbstractThree components of the kinetic friction of snow are described but only the lubricated component of friction is treated in detail. This component depends upon the thickness of water films which support a slider on snow grains over a small fraction of its area. The thickness of the film decreases with ambient temperature in a manner which is sensitive to the thermal conductivity of the slider. The minimum value of friction at any temperature is reached at an intermediate value of speed because friction decreases as the slider first begins to move and the films form but then increases at higher speeds because of the shear resistance. At sub-freezing temperatures a small area in the front part of the slider is dry and the friction is high. Once the water film is formed it increases in thickness towards an equilibrium value which can be very sensitive to slider properties, speed, and temperature. It appears that the mechanisms may be very different for hydrophobic and hydrophilic sliders. From the equations derived here it is clear why friction decreases with repeated passes over the same snow.
The Nature and Origin of a Jökulhlaup Near Casey Station, Antarctica
Authors: Goodwin I.D. 
Published: September 2017

AbstractA jökulhlaup event of 6 months duration occurred near Casey Station, Law Dome, Antarctica, in late March (austral autumn) 1985. This was followed by sporadic outbursts during the austral autumn and winter of 1986. The event is the first recorded outburst of water from beneath a cold ice-cap terminus on Law Dome and, to the author’s knowledge, in Antarctica. From the results of oxygen-isotope and solute analysis, the water was found to have originated as basal melt water. It contained a high total solute load with a dominant enrichment in alkalis, indicting that it had been squeezed through subglacial sediments for an extensive time period. Evidence from the subglacial topography, basal ice exposures, and the sedimentology of nearby supraglacial moraines supports the presence of an ice-marginal subglacial water reservoir as the jökulhlaup source.
Effects of Climatic Perturbations on the Surface-Ablation Regime of the Greenland Ice Sheet, West Greenland
Authors: Ambach W. 
Published: September 2017

AbstractThe shift of the equilibrium-line altitude by climatic perturbations of air temperature δTa, absolute humidity δρv, cloudiness δw and annual accumulation 6c in West Greenland (EGIG profile) is analyzed by heat-balance modelling. The perturbations δTa = +1 K, δρv = +0.25 g m−3, δc = +50 kg m−2 result in a shift of the equilibrium-line altitude of 87.5, 9.8, and −24.3 m, respectively, while perturbations in cloudiness are negligible. The most important influence originates from changing air temperature, as air temperature affects daily heat-flux density of melt and duration of the ablation period. In regimes with negative values of the gradient of annual accumulation, the shift of the equilibrium line is enhanced.
Surface Roughness and Bulk Heat Transfer on a Glacier: Comparison with Eddy Correlation
Authors: Munro D. Scott 
Published: September 2017

AbstractMore than 100 simultaneously measured profiles of wind speed and temperature were analyzed to determine the aerodynamic and thermal roughness lengths of glacier ice. The results proved to be extremely sensitive to measurement height, which is difficult to define precisely on the hummocky terrain of a glacier. Therefore, aerodynamic roughness lengths were estimated from the microtopography of the surface, yielding 2.46 mm for ice, and 5.5 mm for snow. Despite the indeterminate nature of the profile analysis, it did support the view that the thermal roughness length must decrease as the roughness Reynolds number increases, a relationship which has been modelled in the literature. Good agreement between bulk-transfer estimates and eddy-correlation measurements of fhe sensible heat-flux density on melting ice and snow was obtained by combining the aerodynamic roughness length with a suitable model for thermal roughness length.
Estimates of Peak Discharge from the Drainage of Ice-Dammed Ape Lake, British Columbia, Canada
Authors: Desloges Joseph R. , Jones David P. , Ricker Karl E. 
Published: September 2017

AbstractThe first known occurrence of outburst flooding at Ape Lake, British Columbia, was in October 1984 following the formation of a subglacial tunnel in an ice dam created by Fyles Glacier. Following tunnel closure, the lake refilled in 150 d and then a second outburst flood occurred in August 1986. During both events, 55% of the Apc Lake volume or 46 × 106m3was released in less than 24 h into the 50 km long, ungauged Noeick River, producing an average discharge of 540 m3s−1. Channel and flood-plain erosion, damage to access roads, bridges, a logging camp, and an airstrip were related to the peak or maximum instantaneous discharge. In the absence of direct measurements, and to facilitate planning for future flood events, several independent methods were employed to estimate peak discharge. A modified version of the Clague-Mathews formula and the slope-area method yield consistent estimates which approach 1600 m3s−1near the ice-dam outlet. Attenuation of the flood peak in Noeick River is as high as 25% in the upper 12 km due to channel and flood-plain storage. Results using Clarke’s (1982) physical-based model suggest lower discharges and may be related to the irregular morphology of Ape Lake. Since Fyles Glacier is in continuous retreat, drainage around the margin of the ice dam which began in the summer of 1987 is expected to continue and no further outburst floods are anticipated.
Distribution of Net Mass Balance in the Vicinity of Crary Ice Rise, Antarctica
Authors: Bindschadler Robert A. , Roberts Eric P. , MacAyeal Douglas R. 
Published: September 2017

AbstractCalculations of the regional variation of net mass balance around Crary Ice Rise, Antarctica, show significant rates of thickening up-stream of the ice rise and significant thinning down-stream (assuming zero basal melting or freezing). Thickening also is occurring on the south-west side of the ice rise nearest the Transantarctic Mountains. These imbalances imply migration of the rise and help explain its current non-equilibrium shape. The pattern of a suture line down-stream of the rise indicates a quasi-periodic mechanism of rift formation.
The Effect of the Specimen–Platen Interface on Internal Cracking and Brittle Fracture of Ice Under Compression: High-Speed Photography
Authors: Schulson E.M. , Gies M.C. , Lasonde G.J. , Nixon W.A. 
Published: September 2017

AbstractUniaxial compression experiments at –10°C at 10−3s−1 on fresh-water, granular ice have established through the use of high-speed photography that internal cracks nucleate preferentially away from the ice/platen (i/p) interface under conditions of i/p contraint, but near the interface under conditions of i/p expansion. Under conditions of little i/p interaction, cracks nucleate more or less randomly throughout the specimen. Correspondingly, the brittle-fracture strength decreases as the i/p interaction changes from compressive to tensile. These effects are explained in terms of the spatial variation of the maximum shear stress and the crack density.