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  • 1
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    Liquid Water in Snow – Workshop 2014 (2014)
    INT GLACIOL SOC
    In:  EPIC3Ice News Bulletin of the International Glaciological Society, INT GLACIOL SOC, ISSN 0(164), 2 p.
    Details
    Publication Date: 2019-07-17
    Description: Report of the Liquid Water in Snow Workshop, Davos, Switzerland, 2–4 April 2014
    Repository Name: EPIC Alfred Wegener Institut
    Type: Miscellaneous , notRev
    Format: application/pdf
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  • 2
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    Surface topography and ice flow in the vicinity of the EDML deep-drilling site, Antarctica (2007)
    INT GLACIOL SOC
    In:  EPIC3Journal of Glaciology, INT GLACIOL SOC, 53(182), pp. 442-448, ISSN: 0022-1430
    Details
    Publication Date: 2019-07-16
    Description: Interpretation of ice-core records requires accurate knowledge of the past and present surface topography and stress–strain fields. The European Project for Ice Coring in Antarctica (EPICA) drilling site (75.00258°S, 0.06848°E; 2891.7 m) in Dronning Maud Land, Antarctica, is located in the immediate vicinity of a transient and forking ice divide. A digital elevation model is determined from the combination of kinematic GPS measurements with the GLAS12 datasets from the ICESat. Based on a network of stakes, surveyed with static GPS, the velocity field around the drilling site is calculated. The annual mean velocity magnitude of 12 survey points amounts to 0.74ma–1. Flow directions mainly vary according to their distance from the ice divide. Surface strain rates are determined from a pentagonshaped stake network with one center point close to the drilling site. The strain field is characterized by along-flow compression, lateral dilatation and vertical layer thinning.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 3
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    Potential mechanisms for anisotropy in ice-penetrating radar data (2012)
    INT GLACIOL SOC
    In:  EPIC3Journal of Glaciology, INT GLACIOL SOC, 58(209), pp. 613-624, ISSN: 0022-1430
    Details
    Publication Date: 2017-10-20
    Description: Radar data (center frequency 150 MHz) collected on the Antarctic plateau near the EPICA deep-drilling site in Dronning Maud Land vary systematically in backscattered power, depending on the azimuth antenna orientation. Backscatter extrema are aligned with the principal directions of surface strain rates and change with depth. In the upper 900 m, backscatter is strongest when the antenna polarization is aligned in the direction of maximal compression, while below 900m the maxima shift by 90◦ pointing towards the lateral flow dilatation. We investigate the backscatter from elongated air bubbles and a vertically varying crystal-orientation fabric (COF) using different scattering models in combination with ice-core data. We hypothesize that short-scale variations in COF are the primary mechanism for the observed anisotropy, and the 900m boundary between the two regimes is caused by ice with varying impurity content. Observations of this kind allow the deduction of COF variations with depth and are potentially also suited to map the transition between Holocene and glacial ice.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
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    Investigating englacial reflections with vibro- and explosive-seismic surveys at Halvfarryggen ice dome, Antarctica (2013)
    INT GLACIOL SOC
    In:  EPIC3Annals of Glaciology, INT GLACIOL SOC, 54(64), pp. 189-200, ISSN: 0260-3055
    Details
    Publication Date: 2019-07-17
    Description: Explosive seismic reflection data from Halvfarryggen, a 910m thick local ice dome of the Antarctic ice sheet, show numerous laterally continuous reflections within the ice between 300 and 870m depth.We compare the quality of data obtained with explosive sources with that obtained using a vibroseis source for detecting englacial reflections with a snowstreamer, and investigate the origin of englacial reflections. We find vibroseis in combination with a snowstreamer is ten times more productive than explosive seismics. However, englacial reflections are more clearly visible with explosives, which have a broader bandwidth signature, than the vibroseis, which is band-limited at the high-frequency end to 100 Hz. Only the strongest and deepest englacial reflection is detected with vibroseis. We interpret the majority of englacial reflections to originate from changes in the crystal orientation fabric in closely spaced layers, less than the vibro-seismic tuning thickness of 13.5 m. Phase analysis of the lowermost englacial reflector, 40m above the bed, indicates a sharp increase in seismic wave speed. We interpret this reflector as a transition to a vertical single-maximum fabric. Our findings support current results from anisotropic ice-flow models, that crystal fabric is highly anisotropic at ice domes, both laterally and vertically.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 5
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    Joint interpretation of explosive and vibroseismic surveys on cold firn for the investigation of ice properties (2013)
    INT GLACIOL SOC
    In:  EPIC3Annals of Glaciology, INT GLACIOL SOC, 54(64), pp. 201-210, ISSN: 0260-3055
    Details
    Publication Date: 2019-07-17
    Description: Two seismic surveys were carried out on the high-altitude glacier saddle, Colle Gnifetti, Monte Rosa, Italy/Switzerland. Explosive and vibroseismic sources were tested to explore the best way to generate seismic waves to deduce shallow and intermediate properties (〈100 m) of firn and ice. The explosive source (SISSY) excites strong surface and diving waves, degrading data quality for processing; no englacial reflections besides the noisy bed reflector are visible. However, the strong diving waves are analyzed to derive the density distribution of the firn pack, yielding results similar to a nearby ice core. The vibrator source (ElViS), used in both P- and SH-wave modes, produces detectable laterally coherent reflections within the firn and ice column.We compare these with ice-core and radar data. The SH-wave data are particularly useful in providing detailed, high-resolution information on firn and ice stratigraphy. Our analyses demonstrate the potential of seismic methods to determine physical properties of firn and ice, particularly density and potentially also crystal-orientation fabric.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 6
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    Characterizing the glaciological conditions at Halvfarryggen icedome, Dronning Maud Land, Antarctic (2013)
    INT GLACIOL SOC
    In:  EPIC3Journal of Glaciology, INT GLACIOL SOC, 59(213), pp. 9-20
    Details
    Publication Date: 2017-10-17
    Description: We present a comprehensive approach (including field data, remote sensing and ananisotropic ice-flow model) to characterize Halvfarryggen ice dome in coastal Dronning Maud Land,Antarctica. This is a potential drill site for the International Partnerships in Ice Core Sciences, which hasidentified the need for ice cores covering atmospheric conditions during the last few millennia. Wederive the surface topography, the ice stratigraphy from radar data, and accumulation rates which varyfrom 400 to 1670kgm–2a–1due to preferred wind directions and changing surface slope. Thestratigraphy shows anticlines and synclines beneath the divides. We transfer Dansgaard–Johnsen age–depth scales from the flanks along isochrones to the divide in the upper 20–50% of the ice thickness andshow that they compare well with the results of a full-Stokes, anisotropic ice-flow model which predicts(1) 11kaBPice at 90% of the ice thickness, (2) a temporally stable divide for at least 2700–4500 years,(3) basal temperatures below the melting point (–128C to –58C) and (4) a highly developed crystalorientation fabric (COF). We suggest drilling into the apices of the deep anticlines, providing a goodcompromise between record length and temporal resolution and also facilitating studies of the interplayof anisotropic COF and ice flow
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 7
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    Influence of ice crystal anisotropy on seismic velocity analysis (2014)
    INT GLACIOL SOC
    In:  EPIC3Annals of Glaciology, INT GLACIOL SOC, 55(67), pp. 97-106, ISSN: 0260-3055
    Details
    Publication Date: 2019-07-17
    Description: ABSTRACT. In 2010 a reflection seismic survey was carried out on the Alpine glacier Colle Gnifetti. The processed and depth-converted data could be compared to a nearby ice core, drilled almost to the bed. Comparisons showed that the depth of the P-wave bed reflection was too shallow, while the depth of the SH-wave bed reflection fitted the ice-core length well. We are now able to explain the major part of these differences using the existing crystal orientations of the ice at Colle Gnifetti. We calculate anisotropic velocities for P- and SH-waves that are usually picked for stacking and compare them with zero-offset velocities needed for the depth conversion. Here we take the firn pack at Colle Gnifetti into account for P- and S-wave analysis. To incorporate the S-wave analysis we first derive a new equation for the relationship between density and S-wave velocity from diving waves. We show that anisotropic fabrics observed at Colle Gnifetti introduce a difference of only 1% between stacking and depth-conversion velocities for the SH-wave, but 7% for the P-wave. We suggest that this difference in stacking and depth-conversion velocity for the P-wave can be used to derive information about the existing anisotropy by combining our seismic data with, for example, radar data.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 8
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    Continuous snowpack monitoring using upward-looking ground-penetrating radar technology (2014)
    INT GLACIOL SOC
    In:  EPIC3Journal of Glaciology, INT GLACIOL SOC, 60(221), pp. 509-525, ISSN: 0022-1430
    Details
    Publication Date: 2019-07-17
    Description: Snow stratigraphy and water percolation are key contributing factors to avalanche formation. So far, only destructive methods can provide this kind of information. Radar technology allows continuous, non-destructive scanning of the snowpack so that the temporal evolution of internal properties can be followed. We installed an upward-looking ground-penetrating radar system (upGPR) at the Weissfluhjoch study site (Davos, Switzerland). During two winter seasons (2010/11 and 2011/12) we recorded data with the aim of quantitatively determining snowpack properties and their temporal evolution. We automatically derived the snow height with an accuracy of about 5 cm, tracked the settlement of internal layers (+-7 cm) and measured the amount of new snow (+-10 cm). Using external snow height measurements, we determined the bulk density with a mean error of 4.3% compared to manual measurements. Radar-derived snow water equivalent deviated from manual measurements by 5%. Furthermore, we tracked the location of the dry-to-wet transition in the snowpack until water percolated to the ground. Based on the transition and an independent snow height measurement it was possible to estimate the volumetric liquid water content and its temporal evolution. Even though we need additional information to derive some of the snow properties, our results show that it is possible to quantitatively derive snow properties with upGPR.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 9
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    Recent work - Germany (2014)
    INT GLACIOL SOC
    In:  EPIC3News Bulletin of the International Glaciological Society, INT GLACIOL SOC, ISSN 0(164), 45 p.
    Details
    Publication Date: 2019-07-17
    Description: Contributions to the IGS Bulletin ICE featuring recent work in Germany.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Miscellaneous , notRev
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  • 10
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    Calibration of a higher-order 3-D ice flow model of the Morteratsch glacier complex, Engadin, Switzerland (2013)
    INT GLACIOL SOC
    In:  EPIC3Annals of Glaciology, INT GLACIOL SOC, 54(63), pp. 343-351, ISSN: 0260-3055
    Details
    Publication Date: 2019-07-17
    Description: We have reconstructed the ice thickness distribution of the Morteratsch glacier complex, Switzerland, and used this to simulate its flow with a higher-order 3-D model. Ice thickness was measured along transects with a ground-penetrating radar and further extended over the entire glacier using the plastic flow assumption and a distance-weighted interpolation technique. We find a maximum ice thickness of 350+-52.5m for the central trunk of Vadret da Morteratsch, resulting from a bedrock overdeepening. The average thickness of the glacier complex is 72.2+-18.0 m, which corresponds to a total ice volume of 1.14+-0.28km3. The flow of the glacier is modelled by tuning the rate factor and the sliding parameters taking into account higher-order terms in the force balance. The observed velocities can be reproduced closely (root-mean-square error of 15.0ma–1, R2 = 0.93) by adopting a sliding factor of 12x10–16m7N–3 a–1 and a rate factor of 1.6x10–16 Pa–3 a–1. In this setting, ice deformation accounts for 70% of the surface velocity and basal sliding for the remaining 30%. The modelled velocity field reaches values up to 125ma–1, but also indicates an almost stagnant front and confluence area, which are crucial for understanding the ongoing glacier retreat.
    Repository Name: EPIC Alfred Wegener Institut
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