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  • 1
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    Surface topography and ice flow in the vicinity of the EDML deep-drilling site, Antarctica
    International Glaciological Society ; 2007
    In:  Journal of Glaciology Vol. 53, No. 182 ( 2007), p. 442-448
    Details
    In: Journal of Glaciology, International Glaciological Society, Vol. 53, No. 182 ( 2007), p. 442-448
    Abstract: 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 (75.0025° S, 0.0684° 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 0.74 m a –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.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.3189/002214307783258512
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2007
    detail.hit.zdb_id: 2140541-4
    SSG: 14
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  • 2
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    Small-scale spatio-temporal characteristics of accumulation rates in western Dronning Maud Land, Antarctica
    International Glaciological Society ; 2008
    In:  Journal of Glaciology Vol. 54, No. 185 ( 2008), p. 315-323
    Details
    In: Journal of Glaciology, International Glaciological Society, Vol. 54, No. 185 ( 2008), p. 315-323
    Abstract: Spatio-temporal variations of the recently determined accumulation rate are investigated using ground-penetrating radar (GPR) measurements and firn-core studies. The study area is located on Ritscherflya in western Dronning Maud Land, Antarctica, at an elevation range 1400–1560 m. Accumulation rates are derived from internal reflection horizons (IRHs), tracked with GPR, which are connected to a dated firn core. GPR-derived internal layer depths show small relief along a 22 km profile on an ice flowline. Average accumulation rates are about 190 kg m −2 a −1 (1980–2005) with spatial variability (1 σ ) of 5% along the GPR profile. The interannual variability obtained from four dated firn cores is one order of magnitude higher, showing 1 σ standard deviations around 30%. Mean temporal variations of GPRderived accumulation rates are of the same magnitude or even higher than spatial variations. Temporal differences between 1980–90 and 1990–2005, obtained from two dated IRHs along the GPR profile, indicate temporally non-stationary processes, linked to spatial variations. Comparison with similarly obtained accumulation data from another coastal area in central Dronning Maud Land confirms this observation. Our results contribute to understanding spatio-temporal variations of the accumulation processes, necessary for the validation of satellite data (e.g. altimetry studies and gravity missions such as Gravity Recovery and Climate Experiment (GRACE)).
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.3189/002214308784886243
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2008
    detail.hit.zdb_id: 2140541-4
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  • 3
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    Origin of englacial stratigraphy at three deep ice core sites of the Greenland Ice Sheet by synthetic radar modelling
    Cambridge University Press (CUP) ; 2022
    In:  Journal of Glaciology Vol. 68, No. 270 ( 2022-08), p. 799-811
    Details
    In: Journal of Glaciology, Cambridge University Press (CUP), Vol. 68, No. 270 ( 2022-08), p. 799-811
    Abstract: During the past 20 years, multi-channel radar emerged as a key tool for deciphering an ice sheet's internal architecture. To assign ages to radar reflections and connect them over large areas in the ice sheet, the layer genesis has to be understood on a microphysical scale. Synthetic radar trace modelling based on the dielectric profile of ice cores allows for the assignation of observed physical properties’ variations on the decimetre scale to radar reflectors extending from the coring site to a regional or even whole-ice-sheet scale. In this paper we rely on the available dielectric profiling data of the northern Greenland deep ice cores: NGRIP, NEEM and EGRIP. The three records are well suited for assigning an age model to the stratigraphic radar-mapped layers, and linking up the reflector properties to observations in the cores. Our modelling results show that the internal reflections are mainly due to conductivity changes. Furthermore, we deduce fabric characteristics at the EGRIP drill site from two-way-travel-time differences of along and across-flow polarized radarwave reflections of selected horizons (below 980 m). These indicate in deeper parts of the ice column an across-flow concentrated c -axis fabric.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.1017/jog.2021.137
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2022
    detail.hit.zdb_id: 2140541-4
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  • 4
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    Surface accumulation in Northern Central Greenland during the last 300 years
    Cambridge University Press (CUP) ; 2020
    In:  Annals of Glaciology Vol. 61, No. 81 ( 2020-04), p. 214-224
    Details
    In: Annals of Glaciology, Cambridge University Press (CUP), Vol. 61, No. 81 ( 2020-04), p. 214-224
    Abstract: The internal stratigraphy of snow and ice as imaged by ground-penetrating radar may serve as a source of information on past accumulation. This study presents results from two ground-based radar surveys conducted in Greenland in 2007 and 2015, respectively. The first survey was conducted during the traverse from the ice-core station NGRIP (North Greenland Ice Core Project) to the ice-core station NEEM (North Greenland Eemian Ice Drilling). The second survey was carried out during the traverse from NEEM to the ice-core station EGRIP (East Greenland Ice Core Project) and then onwards to Summit Station. The total length of the radar profiles is 1427 km. From the radar data, we retrieve the large-scale spatial variation of the accumulation rates in the interior of the ice sheet. The accumulation rates range from 0.11 to 0.26 m a −1 ice equivalent with the lowest values found in the northeastern sector towards EGRIP. We find no evidence of temporal or spatial changes in accumulation rates when comparing the 150-year average accumulation rates with the 321-year average accumulation rates. Comparisons with regional climate models reveal that the models underestimate accumulation rates by up to 35% in northeastern Greenland. Our results serve as a robust baseline to detect present changes in either surface accumulation rates or patterns.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.1017/aog.2020.30
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2020
    detail.hit.zdb_id: 2122400-6
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  • 5
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    Investigating small-scale variations of the recent accumulation rate in coastal Dronning Maud Land, East Antarctica
    International Glaciological Society ; 2007
    In:  Annals of Glaciology Vol. 46 ( 2007), p. 14-21
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 46 ( 2007), p. 14-21
    Abstract: The accumulation rate on Potsdam Glacier, East Antarctica, and its spatial and temporal variations are examined using ground-penetrating radar, snow samples and firn-core studies. Physical properties in snow samples and along firn cores provide distributions of density with depth, showing only small spatial variation. Counting of peaks in δ 18 O along the firn cores yields an age–depth distribution that is transferred to the stratigraphy of isochronal internal layers observed with radar. From two radar horizons we determine the spatial accumulation pattern, averaged over the periods 1970–80 and 1980–2004. The shape of internal layers indicates an ablation area at the eastern margin of the investigation area. Accumulation rates show a very high spatial variability, with a mean value of 141 kgm –2 a –1 for the period 1970–2004 and a standard deviation of almost 50%. Mean temporal variation of only a few per cent throughout the investigated area for the observed time interval is much less than the spatial variations. The mean accumulation values are somewhat less than values reported before from this region. Accumulation pattern and surface topography are linked in a way indicating that wind-borne redistribution of snow significantly contributes to the observed spatial variations of accumulation rates. The accumulation data and their variability complement and validate present and future satellite studies of Antarctica’s mass balance.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.3189/172756407782871756
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2007
    detail.hit.zdb_id: 2122400-6
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  • 6
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    Multiangle, Frequency, and Polarization Radar Measurement of Ice Sheets
    Institute of Electrical and Electronics Engineers (IEEE) ; 2020
    In:  IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing Vol. 13 ( 2020), p. 2070-2080
    Details
    In: IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, Institute of Electrical and Electronics Engineers (IEEE), Vol. 13 ( 2020), p. 2070-2080
    Type of Medium: Online Resource
    ISSN: 1939-1404 , 2151-1535
    URL: Journal
    URL: Article
    DOI: 10.1109/JSTARS.4609443
    DOI: 10.1109/JSTARS.2020.2991682
    Language: Unknown
    Publisher: Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2020
    detail.hit.zdb_id: 2457423-5
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  • 7
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    Comparison of measurements from different radio-echo sounding systems and synchronization with the ice core at Dome C, Antarctica
    Copernicus GmbH ; 2017
    In:  The Cryosphere Vol. 11, No. 1 ( 2017-03-01), p. 653-668
    Details
    In: The Cryosphere, Copernicus GmbH, Vol. 11, No. 1 ( 2017-03-01), p. 653-668
    Abstract: Abstract. We present a compilation of radio-echo sounding (RES) measurements of five radar systems (AWI, BAS, CReSIS, INGV and UTIG) around the EPICA Dome C (EDC) drill site, East Antarctica. The aim of our study is to investigate the differences of the various systems in their resolution of internal reflection horizons (IRHs) and bed topography, penetration depth and capacity of imaging the basal layer. We address the questions of the compatibility of existing radar data for common interpretation and the suitability of the individual systems for reconnaissance surveys. We find that the most distinct IRHs and IRH patterns can be identified and transferred between most data sets. Considerable differences between the RES systems exist in range resolution and depiction of the bottom-most region. Considering both aspects, which we judge as crucial factors in the search for old ice, the CReSIS and the UTIG systems are the most suitable ones. In addition to the RES data set comparison we calculate a synthetic radar trace from EDC density and conductivity profiles. We identify 10 common IRHs in the measured RES data and the synthetic trace. We then conduct a sensitivity study for which we remove certain peaks from the input conductivity profile. As a result the respective reflections disappear from the modeled radar trace. In this way, we establish a depth conversion of the measured travel times of the IRHs. Furthermore, we use these sensitivity studies to investigate the cause of observed reflections. The identified IRHs are assigned ages from the EDC's timescale. Due to the isochronous character of these conductivity-caused IRHs, they are a means to extend the Dome C age structure by tracing the IRHs along the RES profiles.
    Type of Medium: Online Resource
    ISSN: 1994-0424
    URL: Article
    URL: Article
    DOI: 10.5194/tc-11-653-2017
    DOI: 10.5194/tc-11-653-2017-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2017
    detail.hit.zdb_id: 2393169-3
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  • 8
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    Converging flow and anisotropy cause large-scale folding in Greenland's ice sheet
    Springer Science and Business Media LLC ; 2016
    In:  Nature Communications Vol. 7, No. 1 ( 2016-04-29)
    Details
    In: Nature Communications, Springer Science and Business Media LLC, Vol. 7, No. 1 ( 2016-04-29)
    Abstract: The increasing catalogue of high-quality ice-penetrating radar data provides a unique insight in the internal layering architecture of the Greenland ice sheet. The stratigraphy, an indicator of past deformation, highlights irregularities in ice flow and reveals large perturbations without obvious links to bedrock shape. In this work, to establish a new conceptual model for the formation process, we analysed the radar data at the onset of the Petermann Glacier, North Greenland, and created a three-dimensional model of several distinct stratigraphic layers. We demonstrate that the dominant structures are cylindrical folds sub-parallel to the ice flow. By numerical modelling, we show that these folds can be formed by lateral compression of mechanically anisotropic ice, while a general viscosity contrast between layers would not lead to folding for the same boundary conditions. We conclude that the folds primarily form by converging flow as the mechanically anisotropic ice is channelled towards the glacier.
    Type of Medium: Online Resource
    ISSN: 2041-1723
    URL: Article
    DOI: 10.1038/ncomms11427
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2016
    detail.hit.zdb_id: 2553671-0
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  • 9
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    Bed topography and subglacial landforms in the onset region of the Northeast Greenland Ice Stream – CORRIGENDUM
    Cambridge University Press (CUP) ; 2023
    In:  Annals of Glaciology
    Details
    In: Annals of Glaciology, Cambridge University Press (CUP)
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.1017/aog.2023.33
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2023
    detail.hit.zdb_id: 2122400-6
    SSG: 14
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  • 10
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    Bed topography and subglacial landforms in the onset region of the Northeast Greenland Ice Stream
    Cambridge University Press (CUP) ; 2020
    In:  Annals of Glaciology Vol. 61, No. 81 ( 2020-04), p. 143-153
    Details
    In: Annals of Glaciology, Cambridge University Press (CUP), Vol. 61, No. 81 ( 2020-04), p. 143-153
    Abstract: The Northeast Greenland Ice Stream (NEGIS) is an important dynamic component for the total mass balance of the Greenland ice sheet, as it reaches up to the central divide and drains 12% of the ice sheet. The geometric boundary conditions and in particular the nature of the subglacial bed of the NEGIS are essential to understand its ice flow dynamics. We present a record of more than 8000 km of radar survey lines of multi-channel, ultra-wideband radio echo sounding data covering an area of 24 000 km 2 , centered on the drill site for the East Greenland Ice-core Project (EGRIP), in the upper part of the NEGIS catchment. Our data yield a new detailed model of ice-thickness distribution and basal topography in the region. The enhanced resolution of our bed topography model shows features which we interpret to be caused by erosional activity, potentially over several glacial–interglacial cycles. Off-nadir reflections from the ice–bed interface in the center of the ice stream indicate a streamlined bed with elongated subglacial landforms. Our new bed topography model will help to improve the basal boundary conditions of NEGIS prescribed for ice flow models and thus foster an improved understanding of the ice-dynamic setting.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.1017/aog.2020.12
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2020
    detail.hit.zdb_id: 2122400-6
    SSG: 14
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