bluuebunny/crossref_metadata_2025_split huggingface dataset:
Concerning the Deposition and Diagenesis of Strata in Polar Firn
Authors: Alley Richard B. 
Published: September 2017

AbstractDepth hoar in polar firn forms when large temperature gradients act on low-density firn, but high-density firn does not develop into depth hoar. Low densities in firn may be depositional (burial of surface hoar or still-air snowfall) or diagenetic (mass loss to the free atmosphere, typically in autumn); however, diagenesis is sufficiently strong to cause significant mass loss only in the top 50–100 mm of firn. Between about 50–100 mm and 2 m depth, grain growth and densification are accelerated strongly by temperature-gradient effects; from 2 to 5 m, temperature gradients have a small but measurable effect on rates of processes in firn, and below 5 m rates essentially have isothermal values.Diagenetic depth-hoar layers typically develop in the autumn, are relatively thick, and have smooth bases. Depositional depth-hoar layers may develop at any season, are relatively thin, and have irregular bases. In low-accumulation regions, visual stratification may preserve only an annual signal, but in high-accumulation regions individual storms or other features may be recognizable.
Analysis of Trace Elements in the Bhq Ice Core, Law Dome, Antarctica
Authors: Yun-Gang Liu , Yun-Hui Zhang , Gui-Qun Li , Lun Xiao , Zi-Chu Xie 
Published: September 2017

AbstractTrace elements in ice samples taken from Law Dome, Antarctica, were analysed using an instrumental neutron-activation analysis technique. A Jupiter multichannel analyser-computer system coupled to a Ge(Li) detector was used for the acquisition of γ-spectra and for data reduction. “Blanks” in water and in nitric acid, which were used in pre-concentration and sample transfer, were also analysed. To check the validity of this analytical procedure, a U.S. Environment Protection Agency water standard for trace elements was also analysed. The observed values agreed with the certified values.The results (in ppb) of eight elements are:Na 209 Mn 0.42 Mg 26 Fe 14Sc 0.0017 Co 0.028 Al 9.6 Se 0.02The enrichment factors for these eight elements relative to the Earth’s crust were calculated. These elements can be subdivided into three groups or sources according to their enrichment factors. The variations of elemental concentrations with depth show no positive tendency towards a systematic increase or decrease over the past 5000 years.
Temporal Variations of Isotopic Composition of Glacier-River Water During Summer: Observations at Austre Okstindbreen, Okstindan, Norway
Authors: Theakstone Wilfred H. 
Published: September 2017

AbstractThe isotopic composition of river water discharging from the Norwegian glacier, Austre Okstindbreen, in summer varies on both daily and longer-term scales. Most δ18o values of samples from the principal river are within the range −12.5 to −14.0‰). Because new snow tends to be relatively depleted of 8180, water leaving the glacier early in the summer has low δ18O values. Subsequently, values rise as contributions of old snow, glacier ice, and their melt waters, which are isotopically heavier (median δ18O values generally above −12.0‰) dilute the δ18O depleted base-flow component of discharge, a mixture of waters with different histories of formation, storage, and transit. Accumulation-area melting contributes significantly to river discharge. Towards the end of the summer, as surface melting declines, δ18O values tend to fall. Between-year differences of within-summer trends reflect differences of development of the glacier’s drainage systems. The drainage systems are affected by outbursts from a glacier-dammed lake. During fine weather, δ18o variations follow the diurnal cycle of surface melting: they are strongly correlated with, but lag behind, air temperatures. Perturbations during rainfall cannot be explained simply in terms of the isotopic composition of the precipitation, since low values may be associated with isotopically heavy rainfall. Displacement of water previously stored within or below the glacier may account for the anomaly. Contrasts of composition characterize different rivers leaving the glacier, because the relative contributions of various water sources differ.
Dynamics of the Ice-Crushing Process
Authors: Jordaan Ian J. , Timco Garry W. 
Published: September 2017

AbstractDuring fast indentation tests on ice sheets at constant rates, crushing is commonly observed at appropriate combinations of speed and aspect ratio. An analysis is made of this mode of failure, using as a basis a recently conducted test on an ice sheet under controlled conditions. The variation of load with time is given special attention, and cyclic variation of load is associated with periodic crushing (pulverization) events, followed by clearing of the crushed ice particles. An analysis of the clearing process is summarized in the paper, treating the crushed ice as a viscous material. A detailed analysis of the energy exchanges during the indentation process is given. Elastic variations of stored energy in the indenter and in the ice sheet are calculated; these are relatively minor. The dissipation of energy during a typical load cycle (3 mm movement during 0.05 s) is about 8 J. The energy required to create surfaces of the crushed ice particles is small (0.006 J), as is the work of crushing based on mechanical testing (0.09 J). It is concluded that the process of viscous extrusion of crushed ice is the main seat of energy dissipation, basically as a frictional process. A relationship for the mean thickness of the crushed ice layer is developed, based on energy-balance considerations.
Rock Glaciers of the Dalton Range, Kluane Ranges, South-West Yukon Territory, Canada
Authors: Johnson Peter G. , Lacasse Diane 
Published: September 2017

AbstractGlaciated valleys of the Dalton Range in the south-west Yukon Territory are dominated by rock glaciers identified as glacier ice-cored debris systems. The two rock glaciers studied have different amounts of deformation at present, resulting from post-formation mechanics.The primary formation of lobes of the rock glaciers resulted from periods of glacier activity in the Neoglacial, although older lobes, probably late Pleistocene in age, occur below the Neoglacial lobes. The hydrological systems of the rock glaciers have played a major role in the post-formation deformation of the land forms and the present drainage system is entirely sub-surface. The explanation for the extensive occurrence of rock glaciers in the Dalton Range is lithological as a result of the high susceptibility of the Upper Jurassic/Lower Cretaceous sediments to frost action and glacier erosion.
Instruments and Methods: A Portable Digital Data-Acquisition System for Surface-Based Ice-Radar Studies
Authors: Jacobel Robert W. , Anderson Stefan K. , Rioux Dennis F. 
Published: September 2017

AbstractWe have built a radio-echo sounder which utilizes a low-frequency broad-band impulse transmitter and a microprocessor-based digital-recording system. The unit is mounted on skis and power is delivered by a small generator and batteries. The receiver uses a portable digital storage oscilloscope which passes data via a microprocessor unit to a cassette tape for off-line analysis on a personal computer. Though originally intended primarily for sounding temperate ice, the system has been tested in the Antarctic during the 1987–88 field season with good results. The radar performed well there and also in field tests and subsequent studies on South Cascade Glacier, Washington, and many interesting results were obtained. An oblique incidence profile, where transmitter-receiver separation varied, was used to study the dielectric permittivity of the ice and to locate internal layers at shallow depths. The sounder was also deployed in conjunction with hot-water drilling experiments attempting to create cavities at known locations within the ice. Wave forms from different transmitter–receiver orientations around the bore hole were combined in the off-line analysis to produce a more directional synthetic aperture emphasizing returns from the bore-hole region. Changes in the radar echoes from within the ice were not seen during these experiments, possibly because the drilling was not able to create regions with dimensions or orientations approximating those of naturally occurring cavities.
Measurement of Outflow from a Snowbank with Basal Ice
Authors: Young Kathy L. , Lewkowicz Antoni G. 
Published: September 2017

AbstractA technique is described for measuring melt-water outflow from snowbanks that develop a basal ice layer. The method involves excavation of channels across ice exposed at the lower edge of a snowbank in order to divert run-off into a portable flume. Since discharges are measured before the water comes into contact with the soil, sub-surface flow and soil-moisture changes do not have to be assessed. Outflow discharges recorded at a perennial snowbank site on Melville Island, N.W.T., Canada, compare favourably with energy-balance calculations and measurements of ablation.
In-Situ Measurements of the Activation Energy for D.C. Conduction in Polar ice
Authors: Bently Charles R. 
Published: September 2017

AbstractElectrical resistivity measurements were carried out at station J9 on the Ross Ice Shelf where temperature measurements were available to a depth exceeding three-quarters of the thickness of the shelf. As in a previously published study at a point about 30 km up-steam (Bentley, 1977), the apparent resistivities fit well to a model based upon a steady-state ice shelf with zero bottom balance-rate and an apparent activation energy in the solid ice of 0.15 to 0.25 eV (14–24. kJ mol−1), with preference for the lower end of the range. This model also fits the observed temperature data almost perfectly. Causes of resistivity variation with depth other than the temperature, such as impurity content, metamorphic history, grain size and crystal orientation, probably do not strongly affect the resistivity depth function. Our conclusion is that the true activation energy in the solid ice is less than 0.25 eV (24 kJ mol−1) and perhaps as small as 0.15 eV (14 kJ mol−1), although a reduction by a factor of two or three in the ionic impurity concentration between 50 and 250 m depth cannot be entirely ruled out as a cause of the low apparent temperature effect. A note added in proof indicates that Herron and Langway (in press) have, in fact, reported a decrease in Na+ concentration with increasing depth by a factor of two or three.
Rhombus and Rhomboid Parallelogram Patterns on Glaciers: Natural Indicators of Strain
Authors: Waag Charles J. , Echelmeyer Keith 
Published: September 2017

AbstractSubtle rhombus and rhomboid parallelogram patterns occur on Vaughan Lewis Glacier and the Gilkey Glacier System, Juneau Icefield, Alaska. The patterns are within the firn at the firn-ice interface, are formed by differential recrystallization within narrow preferred zones, and are apparently manifestations of stresses transferred upward from the glacier ice. On the glaciers of the Gilkey System the patterns occur where intense lateral shortening is indicated by abrupt convergence of medial moraines and an abundance of extension crevasses. The short axes of the rhombi and the obtuse angle bisectors of the rhomboids are subparallel to the strike of extension crevasses, therefore to the axis of shortening. The long axes of the rhombi and the acute angle bisectors of the rhomboids are parallel to the foliation, and ice-flow direction. The angles of the parallelograms are variable locally, but average 105° and 75°; the variation seems to reflect intensity and duration of stress. Similar parallelograms occur within the troughs of wave bulges below the Vaughan Lewis Icefall. In the wave bulges, the foliation arcs parallel the wave. The long axes of the rhombi and acute angle bisectors of the rhomboids parallel the foliation around the foliation arc. The short axes of the rhombi and the obtuse angle bisectors of the rhomboids parallel the strikes of radial crevasses, are perpendicular to the direction of extension, and form a fan divergent down-stream. The precise mechanisms and conditions of formation of the parallelograms are not yet understood. Preliminary strain-rate measurements suggest, however, that correlations exist between the orientations of the principal strain-rates and the axes of the patterns, and between the magnitude of the strain-rates and the axial lengths of the patterns.
Some Results from a Linear-Viscous Model of the Arctic Ice Cover
Authors: Hibler W. D. , Tucker W. B. 
Published: September 2017

AbstractIn order to assess the effect of non-local stress transferral through the ice cover empirically, a linear viscous model (employing both bulk and shear viscosities) is used to predict drift-rates for one Soviet and two U.S. drifting stations over the time period May 1962 to April 1964. The predictions, based on available atmospheric pressure and ocean-current data, are compared to free-drift results and to observed values. The empirical viscosity values giving the best fit to observations show a pronounced seasonal variation that correlates well with the growth rate of thin ice. Drift predictions, especially long-term net drift results, show drift magnitudes and turning angles to be simulated significantly better by a viscous model than by a free-drift model. The effects of steady currents are shown to be small for velocities averaged over days but significant for averages over years.
Reconstructed Pleistocene Ice-Sheet Temperatures and Glacial Erosion in Northern Scotland
Authors: Gordon John E. 
Published: September 2017

AbstractPleistocene ice-sheet temperatures are reconstructed for a west-to-east transect across northern Scotland at the ice maximum using the temperature-profile model of Budd and others (1971[a]). Basal freezing is predicted for the central area of the ice sheet, and zones of basal melting on each side to the west and east. Variations in estimates of annual accumulation rate and ice thickness do not greatly alter this general pattern. However, small errors in estimating mean annual temperature at the ice edge and ice-surface temperature lapse-rate may significantly change the pattern of predicted basal temperature regimes, and basal freezing may have extended over the whole of the area considered. Zones of areal scouring occur in both the west and east of the transect but are absent from the central mountain area. Under some of the temperature conditions modelled there is a partial spatial coincidence of the areal scouring in the west with predicted areas of basal melting, but almost none in the east. Possibly this is explained because glacial erosion relates to time periods other than the ice maximum.
Forms at the Base of Till Strata as Indicators of Ice Movement
Authors: Ehlers J. , Stephan H.-J. 
Published: September 2017

AbstractThe direction of inland ice movement can, in some cases, be reconstructed by a study of the forms at the base of till strata. These forms are “ribs”, which are formed either as slickensides or as a type of negative “flute”; “edges” and “wedges”, which are caused by shearing movements at the base of the ice; or “undulations”, probably created by restricting movements at the base of the ice. These forms appear to be elongated in the direction of ice movement. As these features can easily be measured, they can be used to check, supplement, or replace the results of till-fabric measurements.
Measurements of CO2 and CH4 concentrations in air in a polar ice core
Authors: Nakazawa Takakiyo , Machida Toshinobu , Esumi Kenji , Tanaka Masayuki , Fujii Yoshiyuki , Aoki Shuhji , Watanabe Okitsugu 
Published: September 2017

AbstractDry and wet air-extraction systems and precise analysis systems of the CO2 and CH4 concentrations for a polar ice core were developed to reconstruct their ancient levels. A dry-extraction system was capable of crushing an ice sample of 1000 g into fine powder within 2 min, and its air-extraction efficiency was found to be 98%. The CO2 and CH4 concentrations of extracted air were determined using gas chromatography with a flame-ionized detector. The overall precision of our measurements, including air extraction, was estimated to be better than ± 1 ppmv for CO2 and + 10 ppbv for CH4. Preliminary analysis of the ice core drilled at Mizuho Station, Antarctica, showed that the CO2 and CH4 concentrations at 3340–3700 year BP were about 280 ppmv and 700ppbv, respectively. The Yamato core drilled at the terminus of the glacial flow near the Yamato Mountains, Antarctica, yielded concentrations of 230–240 ppmv for CO2 and 520–550 ppbv for CH4, suggesting that the core had formed during the glacial period.
Seasonal variation of ice ablation at the margin of the Greenland ice sheet and its sensitivity to climate change, Qamanârssûp sermia, West Greenland
Authors: Braithwaite Roger J. , Olesen Ole Β. 
Published: September 2017

AbstractMonthly ice ablation was measured at the margin of the Greenland ice sheet for June, July and August over 7 years (1980–86). The total winter ablation (September-May) has also been measured, and a simple ablation-temperature model used to assign ablation values to individual months. Under the present climate, the most ablation occurred in June-August (on average 81% of annual ablation), moderate ablation took place in May and September (17%) and very little ablation occurred in October-April (2%). The effect of climate change on ice ablation is simulated using the ablation model to recalculate ablation for higher temperatures. Summer ice ablation increases with temperature in the model, but there is proportionally greater increase for May and September, whereas the period from October to April is presently so cold that even a temperature rise of +5 °C will hardly increase ablation. The difference in annual ice ablation caused by future climate change will therefore depend upon the seasonal distribution of the temperature change. Changes in precipitation and accumulation will further modify the seasonal variation of ablation.
Weertman regelation, multiple refreezing events and the isotopic evolution of the basal ice layer
Authors: Hubbard Bryn , Sharp Martin 
Published: September 2017

AbstractA simple model is developed to simulate the isotopic fractionation which accompanies Weertman regelation at the bed of temperate-based glaciers. The fractionation equations of Jouzel and Souchez (1982) are applied to multiple refreezing events over measured glacier-bed profiles, and mass balance is maintained as the basal ice and meltwater produced at one bedrock hummock enter the next. Simulation results indicate that undeformed regelation ice layers are on the order of millimetres to centimetres thick, often being completely melted at the stoss face of certain hummocks and exceptionally reaching a thickness in excess of 10 cm. Neither the internal morphology nor the isotopic composition of these layers is constant, but both vary down-glacier in accordance with bedrock configuration. A glacier-wide fractionation process is identified whereby heavy isotopes are preferentially removed from the basal meltwater film and incorporated into the basal ice. This process might go some way to explaining the anomalously “light” isotopic composition measured in base-flow waters leaving some glaciers. Vertical isotope profiles through undeformed basal ice layers are reconstructed and show that significant isotopic excursions can occur at a scale of millimeteres, while the range of isotopic compositions within such multi-layered regelation ice is greater than that which would occur in ice produced by a single refreezing event. In circumstances where the regelation system is disrupted by removal of film waters into a network of linked cavities, it is found that the remaining basal ice may be significantly enriched in heavy isotopes relative to the composition of the initial mass inputs to the system. Heavy isotope enrichment of this magnitude and consideration of the thickness of the basal ice layers concerned may explain the absence of recorded basal ice samples heavy enough to have been formed in equilibrium with subglacial precipitates sampled at one of the sites (Glacier de Tsanfleuron) and reported in an earlier paper.
Vector analysis of ice-fabric data
Authors: Ferrick M.G. , Claffey K.J. 
Published: September 2017

AbstractThe mechanical properties of ice are strongly affected by crystal texture and c-axis alignment. In this paper, we develop a general quantitative method for analysis of uniaxial crystal-orientation data. These data are represented as unit vectors from the origin with end points on the surface of a unit sphere. An orthogonal least-squares error measure is used to develop equations that define the closest plane and line through the data. The resulting eigenvalue problem is identical to that obtained by other investigators using different methods. However, here we identify an implicit assumption in the method, and observe that the error measure represents physical distance and quantifies the goodness of fit to the data of idealized structures. Also, a method is developed to transform the data and the results for viewing on Schmidt nets drawn in the best plane and the predominant basal plane of a sample, in addition to the standard xy-plane. Applications of the analysis to sea-ice samples include both numerical and Schmidt-net presentations of results.
Patterns of calculated basal drag on ice streams B and C, Antarctica
Authors: Whillans I. M. , Van der Veen C.J. 
Published: September 2017

AbstractPatterns of strain rate and slope on the ice streams are unusual. They cannot be accounted for in the usual way as due to standing waves in ice flow over a basal obstruction to flow (such as a sticky spot). The features are studied using the force-budget technique. The conventional flow law is used, together with measurements of surface strain rate and shape of the glacier, to compute basal drag. The results for Ice Stream C are as expected, in that the drag varies from site to site but is directed inland, restraining the flow. The calculated drag at the base of Ice Stream B, on the other hand, is in places such that it acts to propel the glacier forward. This result is untenable. Either the conventional flow law is not applicable to Ice Stream Β or there are large spatial variations in ice stiffness, perhaps associated with foliation, or both.
In search of ice-stream sticky spots
Authors: Alley Richard B. 
Published: September 2017

AbstractThe basal shear stress of an ice stream may be supported disproportionately on localized regions or “sticky spots”. The drag induced by large bedrock bumps sticking into the base of an ice stream is the most likely cause of sticky spots. Discontinuity of lubricating till can cause sticky spots, but they will collect lubricating water and therefore are unlikely to support a shear stress of more than a few tenths of a bar unless they contain abundant large bumps. Raised regions on the ice-air surface can also cause moderate increases in the shear stress supported on the bed beneath. Surveys of large-scale bed roughness would identify sticky spots caused by bedrock bumps, water-pressure measurements in regions of thin or zero till might reveal whether they were sticky spots, and strain grids across the margins of ice-surface highs would show whether the highs were causing sticky spots. Sticky spots probably are not dominant in controlling Ice Stream Β near the Upstream Β camp, West Antarctica.