bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fennoscandian palaeoglaciology reconstructed using a glacial geological inversion model
Authors: Kleman Johan , Hättestrand Clas , Borgström Ingmar , Stroeven Arjen 
Published: September 2017

AbstractThe evolution of ice-sheet configuration and flow pattern in Fennoscandia through the last glacial cycle was reconstructed using a glacial geological inversion model, i.e. a theoretical model that formalises the procedure of using the landform record to reconstruct ice sheets. The model uses mapped flow traces and deglacial melt-water landforms, as well as relative chronologies derived from cross-cutting striae and till lineations, as input data. Flow-trace systems were classified into four types: (i) time-transgressive wet-bed deglacial fans, (ii) time-transgressive frozen-bed deglacial fans, (iii) surge fans, and (iv) synchronous non-deglacial (event) fans. Using relative chronologies and aggregation of fans into glaciologically plausible patterns, a series of ice-sheet Configurations at different time slices was erected. A chronology was constructed through correlation with dated stratigraphical records and proxy data reflecting global ice volume. Geological evidence exists for several discrete ice-sheet configurations centred over the Scandinavian mountain range during the early Weichselian. The build-up of the main Weichselian Fennoscandian ice sheet started at approximately 70 Ka, and our results indicate that it was characterised by an ice sheet with a centre of mass located over southern Norway. This configuration had a flow pattern which is poorly reproduced by current numerical models of the Fennoscandian ice sheet. At the Last Glacial Maximum the main ice divide was located overthe Gulf of Bothnia. A major bend in the ice divide was caused by outflow of ice to the northwest over the lowest part of the Scandinavian mountain chain. Widespread areas of preserved pre-late-Weichselian landscapes indicate that the ice sheet had a frozen-bed core area, which was only partly diminished in size by inward-transgressive wet-bed zones during the decay phase.
Pleistocene ice at the bottom of the Vavilov ice cap, Severnaya Zemlya, Russian Arctic
Authors: Stiévenard Michel , Nikolaëv Vladimir , Bol’shiyanov Dmitri Yu , Fléhoc Christine , Jouzel Jean , Klementyev Oleg L. , Souchez Roland 
Published: September 2017

AbstractThe Vavilov ice cap was perforated in 1988 by a drilling which reached the underlying frozen sediments. In contrast to the overlying glacier ice, the basal ice is composed of different ice layers with a variable debris load. The stable-isotope composition of these layers shows δ values much lower than everywhere else in the core or in the Vavilov ice cap. This is most probably the signature of a remnant of Pleistocene ice which, for the first time, is shown to occur in the Russian Arctic.
Surface velocity and mass balance of Ice Streams D and E, West Antarctica
Authors: Bindschadler Robert , Vornberger Patricia , Blankenship Donald , Scambos Ted , Jacobel Robert 
Published: September 2017

AbstractOver 75 000 surface-velocity measurements are extracted from sequential satellite imagery of Ice Streams D and E to reveal a complex pattern of flow not apparent from previous measurements. Horizontal and vertical strain rates, calculated from surface velocity, indicate that the bed experiences larger basal shear where the surface of these ice streams is rougher. Ten airborne-radar profiles and one surface-based radar profile of ice thickness make possible the calculation of mass balance for longitudinal sections of each ice stream. Improved data-collection methods increase data density, substantially reducing random errors in velocity. However, systematic errors continue to limit the ability of the flux-differencing technique used here to resolve local variations in mass balance. Nevertheless, significant local variations in mass balance are revealed, while, overall, Ice Streams D and E are in approximate equilibrium. An earlier estimate of the net mass balance for Ice Stream D is improved.
Airborne surface profiling of glaciers: a case-study in Alaska
Authors: Echelmeyer Κ. A. , Harrison W. D. , Larsen C. F. , Sapiano J. , J. E. Mitchell , De Mallie J. , Rabus B. , Adalgeirsdóttir G. , Sombardier L. 
Published: September 2017

AbstractA relatively lightweight and simple airborne system for surface elevation profiling of glaciers in narrow mountain valleys has been developed and tested. The aircraft position is determined by kinematic global positioning system (GPS) methods. The distance to the glacier surface is determined with a laser ranger. The accuracy is about 0.3 m, sufficient to permit future changes to be observed over short time intervals. Long-term changes can be estimated by comparison of profiles with existing maps. Elevation profiles obtained in 1993–94 from three glaciers in central and south-central Alaska are compared with maps made about 1950. The resulting area-averaged, seasonally corrected thickness changes during the interval are: Gulkana Glacier (central Alaska Range)–11 m, Worthington Glacier (central Chugach Mountains) +7 m, and Bear Lake Glacier (Kenai Mountains) −12 m. All three glaciers retreated during the interval of comparison. The estimated uncertainty in the average thickness change is ±5 m. which is mainly due to errors in the existing maps. Constraints on the accuracy of the maps are obtained by profiling in proglacial areas.
Estimation of ice-sheet motion using satellite radar interferometry: method and error analysis with application to Humboldt Glacier, Greenland
Authors: Joughin Ian , Kwok Ron , Fahnestock Mark 
Published: September 2017

AbstractSatellite radar interferometry provides glaciologists with an important new tool for determining the motion and topography of large ice sheets. We examine the sources of error in interferometrically derived ice-motion measurements, including those errors due to inaccurate estimates of the interfero-metric baseline. Several simulations are used to assess baseline accuracy in terms of tie-point error and the number and distribution of tie points. These results give insight into how best to select tie points, and also demonstrate the level of accuracy that can be achieved. Examination of two representative cases likely to occur in mapping ice-sheet motion leads to the conclusion that with adequate tie-point information ice velocity can be measured accurately to within a few meters per year. A method to correct horizontal velocity estimates for the effect of vertical displacement using surface slopes is also developed. Finally, we estimate the single-component velocity field for an area on Humboldt Glacier, northern Greenland, using interferograms formed from ERS-1 SAR image. We estimatе that these velocity measurements are accurate to within 2.3 m year1.
A new high-precision borehole-temperature logging system used at GISP2, Greenland, and Taylor Dome, Antarctica
Authors: Clow Gary D. , Saltus Richard W. , Waddington Edwin D. 
Published: September 2017

AbstractWe describe a high-precision (0.1–1.0 mK) borehole-temperature (BT) logging system developed at the United States Geological Survey (USGS) for use in remote polar regions. We discuss calibration, operational and data-processing procedures, and present an analysis of the measurement errors. The system is modular to facilitate calibration procedures and field repairs. By interchanging logging cables and temperature sensors, measurements can be made in either shallow air-filled boreholes or liquid-filled holes up to 7 km deep. Data can be acquired in either incremental or continuous-logging modes. The precision of data collected by the new logging system is high enough to detect and quantify various thermal effects at the milli-Kelvin level. To illustrate this capability, we present sample data from the 3 km deep borehole at GISP2, Greenland, and from a 130 m deep air-filled hole at Taylor Dome, Antarctica. The precision of the processed GISP2 continuous temperature logs is 0.25–0.34 mK, while the accuracy is estimated to be 4.5 mK. The effects of fluid convection and the dissipation of the thermal disturbance caused by drilling the borehole are clearly visible in the data. The precision of the incremental Taylor Dome measurements varies from 0.11 to 0.32 mK. depending on the wind strength during the experiments. With this precision, we found that temperature fluctuations and multi-hour trends in the BT measurements correlate well with atmospheric-pressure changes.
The determination of glacier speed by time-lapse photography under unfavorable conditions
Authors: Harrison W.D. , Echelmeyer K.A. , Cosgrove D.M. , Raymond C. F. 
Published: September 2017

AbstractTwo practical problems in the use of time-lapse photography for the measurement of speed were encountered during the recent surge of West Fork Glacier in the central Alaska Range, Alaska, U.S.A. The first is severe rotational camera instability; we show how natural, unsurveyed features on the valley wall can be used to make the necessary corrections. The second problem is the computation of absolute speed when many different, unsurveyed glacier-surface features are used as targets. We give a method for connecting the data obtained from different targets, and for determining the scale using limited information obtained by surveying. Severe systematic errors can occur unless the angle between the axis of the lens and the direction of horizontal motion is determined.
Recent fluctuations of glaciers in Valtellina (Italian Alps) and climatic variations
Authors: Pelfini Manuela , Smiraglia Claudio 
Published: September 2017

AbstractValtellina, located in the Italian Alps of Lombardy, is extensively glaciated. Since 1925, terminal variations of the glaciers have been recorded. By analysing a significant sample of valley glaciers, we have recognized a rapid retreat of the termini which occurred between 1925 and the early 1970s. A period of advance followed, which stopped in the second half of the 1980s. The mean summer-temperature fluctuations at the meteorological station of Sondrio at the centre of Valtellina, show that the period 1925–52 was very warm, and then the temperatures dropped. The most intense winter precipitation occurred in the period 1925–37. The behaviour of these glaciers is similar to that of other Alpine glaciers, although time of response may be different.
Sea-ice motion in the Weddell Sea from drifting-buoy and AVHRR data
Authors: Crane David , Wadhams Peter 
Published: September 2017

AbstractA study of sea ice in the northern Weddell Sea was done, relating the ice motion, determined using an array of satellite-tracked drifters, deployed into ice floes, to parameters describing the nature of the ice cover, obtained from an analysis of Advanced Very High Resolution Radiometer (AVHRR) imagery. It was found that the ice motion was predominantly wind-driven, responding to the passage of low-pressure systems across the area. The correlation length of the strain field over the entire measurement period was around 200 km. At high concentrations the ice responded as a rigid body with coherent motion, but below a concentration of around 93%, differential motion occurred. The nature of the ice motion was found to depend upon the lead parameters, with low values of pure convergence and divergence and larger values of vorticity and deformation of the ice field. The vorticity was found to be well correlated with the atmospheric pressure, with a time lag of less than 3 h, implying an almost instantaneous response of the ice cover to meteorological forcing.
Interferometric radar observations of Glaciar San Rafael, Chile
Authors: Rignot Eric , Forster Richard , Isacks Bryan 
Published: September 2017

AbstractInterferometric radar observations of Glaciar San Rafael, Chile, were collected in October 1994 by NASA’s Spaceborne Imaging Radar C (SIR-C) at both L- (24 cm) and C-band frequency (5.6 cm), with vertical transmit and receive polarization. The C-band data did not yield good geophysical products, because the temporal coherence of the signal was significantly reduced alter 24 h. The L-band data were, however, successfully employed to map the surface topography of the icefield with a 10 m uncertainty in height, and measure ice velocity with a precision of 4 mm d−1 or 1.4 m a−1. The corresponding error in strain rates is 0.05 a −1 at a 30 m horizontal spacing. The one-dimensional interferometric velocities were subsequently converted to horizontal displacements by assuming a flow direction and complemented by feature-tracking results near the calving front. The results provide a comprehensive view of the ice-flow dynamics of Glaciar San Rafael. The glacier has a core of rapid flow, 4.5 km in width and 3.5° in average slope, surrounded by slower-moving ice, not by rock. Ice velocity is 2.6 m d−1 or 0.95 km a−1 near the equilibrium-line altitude (1200 m), increasing rapidly before the glacier enters the narrower terminal valley, to reach 17.5 md−1 or 6.4 k ma−1 at the calving front. Strain rates are dominated by lateral shearing at the glacier margins (0.4–0.7 a−1), except for the terminal-valley section, where longitudinal strain rates average close to 1 a−1. This spectacular longitudinal increase in ice velocity in the last few kilometers may be a fundamental feature of tidewater glaciers.
The surface albedo of the Greenland ice sheet: satellite-derived and in situ measurements in the Søndre Strømfjord area during the 1991 melt season
Authors: Knap Wouter H. , Oerlemans Johannes 
Published: September 2017

AbstractThe temporal and spatial variation in the surface albedo of the Greenland ice sheet during the ablation season of 1991 is investigated. The study focuses on an area east of Søndre Strømfjord measuring 200 km by 200 km and centred at 67°5′ N, 48° 13′W. The analysis is based on satellite radiance measurements carried out by the Advanced Very High Resolution Radiometer (AVHRR). The broad-band albedo is estimated from the albedos in channel 1 (visible) and channel 2 (near-infrared). The results are calibrated with the surface albedo of sea and dry snow.Satellite-derived albedos are compared with GIMEX ground measurements at three stations. There is a high degree of consistency in temporal variation at two of the three stations. Large systematic differences are attributed to albedo variations on sub-pixel scale.In the course of the ablation season four zones appear, each parallel to the ice edge. It is proposed that these are, in order of increasing altitude: (I) clean and dry ice, (II) ice with surface water, (III) superimposed ice, and (IV) snow. An extensive description of these zones is given on the basis of the situation on 25 July 1991. Zones I, III and IV reveal fairly constant albedos (0.46, 0.65 and 0.75 on average), whereas zone II is characterised by an albedo minimum (0.34). Survey of the western margin of the Greenland ice sheet (up to 71° N) shows that the zonation occurs between 66° and 70° N.
Measured Re-advance of a Debris-covered Glacier Terminus in the President Range, Yoho National Park, British Columbia, Canada
Authors: Rogerson R.J. 
Published: September 2017

AbstractMeasurements made at the terminus of Emerald Glacier in the Rocky Mountains of Canada indicate terminal re-advance in the order of one to two metres per year sustained since 1978 at least. Re-advance is maximum along that part of the terminus which is heavily covered with supraglacial debris, where ice remains in contact with a push-moraine all summer. Re-advance may represent fluctuations of a small, responsive ice mass, or the early effects of recent climatic deterioration.
Snow Profiles and Avalanche Activity in the Cairngorm Mountains, Scotland
Authors: Ward R. G. W. , langmuir E. D. G. , Beattie B. 
Published: September 2017

AbstractThe paper presents data on the snow cover in the Cairngorm Mountains, Scotland, and compares typical Scottish snow profiles with those measured in alpine, continental, and polar areas. The paper shows that in the Cairngorms snow temperatures are higher and as a result densities and ram penetration resistances are also higher. Typical densities are between 350 and 500 kg m−3 and ram resistances are frequently above 50 or even 100 kg. Typical profiles show large masses of windslab above an equigranular basal layer of old snow, and ice layers are common throughout the profile. Avalanche activity is related to two types of profile both of which share low ram resistance in common. Dry-slab avalanches release when densities are of the order of 250 kg m−3 or less and snow temperatures down to – 10° C in the upper layers. Wet slabs and sluffs fall when the snow is isothermal at the melting point. Densities are usually over 450 kg m−3 and may reach over 600 kgm−3 in slush layers supported by ice lenses.
Derived Characteristics of the Ross Ice Shelf, Antarctica
Authors: Thomas R. H. , MacAyeal D. R. 
Published: September 2017

AbstractResults of the Ross Ice Shelf Geophysical and Glaciological Survey (RIGGS) provide the most complete data set available for any large portion of the polar ice sheets. In this paper, we use the RIGGS data to calculate some of the ice-shelf characteristics. These include steady-state particle trajectories through the ice shelf and the depth of isochronous surfaces, which are of particular importance in choosing a drilling site where ice from the grounded West Antarctic ice sheet is likely to be near the surface. Our estimates for depth to ice originating from the 500 m elevation contour show good agreement with depths to a glaciochemical transition in four ice cores that is believed to be associated with this elevation. This suggests that, for much of the ice shelf, there have been no dramatic and sustained departures from steady state during the past 1500 to 2500 years. With the RIGGS data and an assumed bottom melting rate distribution we calculate steady-state temperature profiles at each of the measurement stations. Then, adopting an ice flow law deduced from laboratory experiments and ice-shelf measurements, we obtain an effective flow-law parameter for each of these sites. Using these values, the measured strain-rate field is transformed to an equivalent stress field over the ice shelf. The stresses are determined by the ice-shelf freeboard and by the force field exerted on the ice shelf by its sides and by grounded ice rises, and our analysis yields estimates of these “restraining” forces F for the Ross ice Shelf. An apparent increase in F very close to the ice front suggests that the ice shelf possesses a narrow seaward fringe of anomalously stiff ice. We suspect that this represents the effects of increased bottom melting rates (and therefore colder and stiffer ice) very close to the ice front. In order to illustrate the role of the restraining forces in controlling ice-shelf behavior, we calculate the strain-rate field for an unrestricted Ross Ice Shelf—one that is detached from its sides and contains no ice rises. Currently the creep-thinning rates for most of the ice shelf is (0.5–1) m year−1; for an unrestricted ice shelf, they would increase to ( 1–10) m year−1, with values up to 60 m year up stream of the ice rises.
210Pb-Dating of Cold Alpine Firn/Ice Cores From Colle Gnifetti, Switzerland
Authors: Gäggeler H. , von Gunten H. R. , Rössler E. , Oeschger H. , Schotterer U. 
Published: September 2017

AbstractThe 210Pb(210Po) method has for the first time been successfully applied for dating cold alpine firn/ice cores. The mean accumulation rate on Grenzgletscher near Colle Gnifetti (Switzerland, altitude 4 450 m) is found to be 37 cm year−1 and 32 cm year−1 for the two ice cores drilled down to 32 m and 65 m in 1976 and 1977, respectively. The surface activity amounts to 4 dpm kg−1 ice. It is shown that a good agreement between the data of the two ice cores is reached with a model taking into account an effect of decreasing annual ice layers with depth. With this thin-out correction, the accumulation rate in the 1977 core increases to 39 cm year−1.
A Note on the Constitutive Law for Sea Ice
Authors: Smith Ronald B. 
Published: September 2017

AbstractThe derivation of a constitutive law to describe large-scale sea-ice deformation commonly uses the so-called “flow rule”. This method introduces a mathematically imposed relationship between shear strength and dilatation which is not based on physical postulates. In this note a more general procedure is described which uses the Reiner–Rivlin equation as a starting point. The method is illustrated by deriving a particular constitutive law and applying it to a simple problem of sea ice blown against a shoreline.
Characteristics of Two Full-Depth Slab Avalanches on Meall Uaine, Glen Shee, Scotland
Authors: William Davison Richard , Keith Davison Steven 
Published: September 2017

AbstractThe characteristics of two full-depth slab avalanches that occurred in 1982 and 1984 at the same location on Meall Uaine in Glen Shee, Scotland, are described. Notable features include the relatively low altitude of the site (c. 670 m) compared to sites of other avalanches observed elsewhere in Scotland, the depth of snow involved (up to 4 m), a snow-pack similar to those recorded in the Cairngorm Mountains, and the entrainment, transport, and deposition of boulders and turf. The probability of the two avalanches occurring when they did was greater than 60%. It is suggested that further observations of full-depth slab avalanches might be obtained by identifying terrain similar to that of the site studied here.
Extrusion Flow Demonstrated by Bore-Hole Deformation Measurements Over a Riegel, Storglaciären, sweden
Authors: Hooke Roger Leb. , Holmlund Per , Iverson Neal R. 
Published: September 2017

AbstractInclinometry measurements in a 126 m bore hole slightly down-glacier from the crest of a riegel on Storglaciären showed what appears to be indisputable extrusion flow during the last 3 weeks of July 1984. The velocity at the bed was about five times that at the surface, and lay in a direction deviating 50–60° from that at the surface. The increase in velocity with depth began more than 50 m above the bed. In August and the first half of September the flow returned nearly to “normal” with only a slight tendency toward extrusion. The flow in July appeared to be related to a period of large diurnal water-pressure variation and cavity opening at the bed up-glacier from the riegel. Decoupling of the ice from the bed on the lowest parts of the riegel may have permitted the extrusion. The return to more “normal” conditions in August appears to have been related to a decrease in ice flux over the riegel and a widening of the zone of decoupling.
Direct Observation of Basal Sliding and Deformation of Basal Drift at Sub-Freezing Temperatures
Authors: Echelmeyer Keith , Zhongxiang Wang 
Published: September 2017

AbstractIn a tunnel at the base of sub-polar Urumqi Glacier No. 1, China, three new mechanisms of glacier flow at sub-freezing temperatures have been observed. Taken individually or in combination, these modes of flow can account for nearly all (60–80%) of the overall glacier motion and, yet, they act only within the lowermost 1–2% of the effective glacier thickness. These mechanisms are: (1) enhanced deformation of the frozen and ice-laden subglacial drift; (2) motion across discrete shear planes or shear bands within the frozen drift or at the ice-drift interface; and (3) basal sliding at an ice-rock interface at a temperature of nearly −5° C. The ice-laden drift has an effective viscosity of more than one hundred times less than that measured in the overlying ice, thus allowing very rapid shear deformation. The observed rate or basal sliding at the ice-rock interface agrees favorably with that predicted by the recent work of Shreve (1984) if proper account is taken of the measured surface roughness and reduced ice viscosity.