GLORIA

GEOMAR Library Ocean Research Information Access

X

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • International Glaciological Society  (18)
  • 1
    Online Resource
    Online Resource
    Joint interpretation of explosive and vibroseismic surveys on cold firn for the investigation of ice properties
    International Glaciological Society ; 2013
    In:  Annals of Glaciology Vol. 54, No. 64 ( 2013), p. 201-210
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 54, No. 64 ( 2013), p. 201-210
    Abstract: 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.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.3189/2013AoG64A200
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2013
    detail.hit.zdb_id: 2122400-6
    SSG: 14
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Online Resource
  • 2
    Online Resource
    Online Resource
    Influence of ice crystal anisotropy on seismic velocity analysis
    International Glaciological Society ; 2014
    In:  Annals of Glaciology Vol. 55, No. 67 ( 2014), p. 97-106
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 55, No. 67 ( 2014), p. 97-106
    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.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.3189/2014AoG67A002
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2014
    detail.hit.zdb_id: 2122400-6
    SSG: 14
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Online Resource
  • 3
    Online Resource
    Online Resource
    Determining the age distribution of Colle Gnifetti, Monte Rosa, Swiss Alps, by combining ice cores, ground-penetrating radar and a simple flow model
    International Glaciological Society ; 2013
    In:  Journal of Glaciology Vol. 59, No. 213 ( 2013), p. 179-189
    Details
    In: Journal of Glaciology, International Glaciological Society, Vol. 59, No. 213 ( 2013), p. 179-189
    Abstract: Ice cores from cold Alpine glaciers may provide unique paleoclimate information from non-polar latitudes. We explore the three-dimensional internal age distribution of the small cold glacier saddle (Colle Gnifetti, Monte Rosa, Italy/Switzerland) to compare the age/depth relations from four local deep ice cores. Tracking isochronous reflection horizons detected by ground-penetrating radar (GPR) among the core locations reveals consistent dating up to 80 years BP. This approach is confined to recent ages, due to the lack of clear reflections below the firn/ice transition. We attempt to overcome this limitation by including a two-dimensional flow model adapted to the GPR-derived surface accumulation and ice thickness distribution. Modeled and GPR isochrones are compared, indicating agreement in shape but featuring a potential offset of 0–3.5 m. The modeled isochrones are interpolated to the core array with ages assigned according to the ice-core datings. The resulting age distribution is consistent up to 110 years BP, with age uncertainties increasing from 7 to 〉 80 years in the lower half of the ice. This combination of methods is novel for Alpine sites and may be adapted for spatial extrapolation of ice properties other than age.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.3189/2013JoG12J072
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2013
    detail.hit.zdb_id: 2140541-4
    SSG: 14
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Online Resource
  • 4
    Online Resource
    Online Resource
    Improved method to determine radio-echo sounding reflector depths from ice-core profiles of permittivity and conductivity
    International Glaciological Society ; 2006
    In:  Journal of Glaciology Vol. 52, No. 177 ( 2006), p. 299-310
    Details
    In: Journal of Glaciology, International Glaciological Society, Vol. 52, No. 177 ( 2006), p. 299-310
    Abstract: We present a technique that modifies and extends down-hole target methods to provide absolute measures of uncertainty in radar-reflector depth of origin. We use ice-core profiles to model wave propagation and reflection, and then cross-correlate the model results with radio-echo sounding (RES) data to identify the depth of reflector events. Stacked traces recorded with RES near the EPICA drill site in Dronning Maud Land, Antarctica, provide reference radargrams, and dielectric properties along the deep ice core form the input data to a forward model of wave propagation that produces synthetic radargrams. Cross-correlations between synthetic and RES radargrams identify differences in propagation wave speed. They are attributed to uncertainties in pure-ice permittivity and are used for calibration. Removing conductivity peaks results in the disappearance of related synthetic reflections and enables the unambiguous relation of electric signatures to RES features. We find that (i) density measurements with g-attenuation or dielectric profiling are too noisy below the firn–ice transition to allow clear identification of reflections, (ii) single conductivity peaks less than 0.5 m wide cause the majority of prominent reflections beyond a travel time of about 10 µs (~900m depth) and (iii) some closely spaced conductivity peaks within a range of 1–2m cannot be resolved within the RES or synthetic data. Our results provide a depth accuracy to allow synchronization of age–depth profiles of ice cores by RES, modeling of isochronous internal structures, and determination of wave speed and of pure-ice properties. The technique successfully operates with dielectric profiling and electrical conductivity measurements, suggesting that it can be applied at other ice cores and drill sites.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.3189/172756506781828674
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2006
    detail.hit.zdb_id: 2140541-4
    SSG: 14
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Online Resource
  • 5
    Online Resource
    Online Resource
    Characteristics and small-scale variability of GPR signals and their relation to snow accumulation in Greenland’s percolation zone
    International Glaciological Society ; 2008
    In:  Journal of Glaciology Vol. 54, No. 185 ( 2008), p. 333-342
    Details
    In: Journal of Glaciology, International Glaciological Society, Vol. 54, No. 185 ( 2008), p. 333-342
    Abstract: We investigate snowpack properties at a site in west-central Greenland with ground-penetrating radar (GPR), supplemented by stratigraphic records from snow pits and shallow firn cores. GPR data were collected at a validation test site for CryoSat (T05 on the Expéditions Glaciologiques Internationales au Groenland (EGIG) line) over a 100 m × 100 m grid and along 1 km sections at frequencies of 500 and 800 MHz. Several internal reflection horizons (IRHs) down to a depth of 10 m were tracked. IRHs are usually related to ice-layer clusters in vertically bounded sequences that obtain their initial characteristics near the surface during the melt season. Warm conditions in the following melt season can change these characteristics by percolating meltwater. In cold conditions, smaller melt volumes at the surface can lead to faint IRHs. The absence of simple mechanisms for internal layer origin emphasizes the need for independent dating to reliably interpret remotely sensed radar data. Our GPR-derived depth of the 2003 summer surface of 1.48 m (measured in 2004) is confirmed by snow-pit observations. The distribution of IRH depths on a 1 km scale reveals a gradient of increasing accumulation to the northeast of about 5 cm w.e. km −1 . We find that point measurements of accumulation in this area are representative only over several hundred metres, with uncertainties of about 15% of the spatial mean.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.3189/002214308784886207
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2008
    detail.hit.zdb_id: 2140541-4
    SSG: 14
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Online Resource
  • 6
    Online Resource
    Online Resource
    Characterizing the glaciological conditions at Halvfarryggen ice dome, Dronning Maud Land, Antarctica
    International Glaciological Society ; 2013
    In:  Journal of Glaciology Vol. 59, No. 213 ( 2013), p. 9-20
    Details
    In: Journal of Glaciology, International Glaciological Society, Vol. 59, No. 213 ( 2013), p. 9-20
    Abstract: We present a comprehensive approach (including field data, remote sensing and an anisotropic 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 has identified the need for ice cores covering atmospheric conditions during the last few millennia. We derive the surface topography, the ice stratigraphy from radar data, and accumulation rates which vary from 400 to 1670 kg m −2 a −1 due to preferred wind directions and changing surface slope. The stratigraphy 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 and show that they compare well with the results of a full-Stokes, anisotropic ice-flow model which predicts (1) 11 ka BP ice at 90% of the ice thickness, (2) a temporally stable divide for at least 2700–4500 years, (3) basal temperatures below the melting point (−12°C to −5°C) and (4) a highly developed crystal orientation fabric (COF). We suggest drilling into the apices of the deep anticlines, providing a good compromise between record length and temporal resolution and also facilitating studies of the interplay of anisotropic COF and ice flow.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.3189/2013JoG12J134
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2013
    detail.hit.zdb_id: 2140541-4
    SSG: 14
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Online Resource
  • 7
    Online Resource
    Online Resource
    Bowling mermaids; or, How do beach ice balls form?
    International Glaciological Society ; 2003
    In:  Journal of Glaciology Vol. 49, No. 167 ( 2003), p. 605-606
    Details
    In: Journal of Glaciology, International Glaciological Society, Vol. 49, No. 167 ( 2003), p. 605-606
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.3189/172756503781830485
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2003
    detail.hit.zdb_id: 2140541-4
    SSG: 14
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Online Resource
  • 8
    Online Resource
    Online Resource
    Continuous snowpack monitoring using upward-looking ground-penetrating radar technology
    International Glaciological Society ; 2014
    In:  Journal of Glaciology Vol. 60, No. 221 ( 2014), p. 509-525
    Details
    In: Journal of Glaciology, International Glaciological Society, Vol. 60, No. 221 ( 2014), p. 509-525
    Abstract: 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.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.3189/2014JoG13J084
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2014
    detail.hit.zdb_id: 2140541-4
    SSG: 14
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Online Resource
  • 9
    Online Resource
    Online Resource
    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
    SSG: 14
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Online Resource
  • 10
    Online Resource
    Online Resource
    Variegated Glacier, Alaska, USA: a century of surges
    International Glaciological Society ; 2005
    In:  Journal of Glaciology Vol. 51, No. 174 ( 2005), p. 399-406
    Details
    In: Journal of Glaciology, International Glaciological Society, Vol. 51, No. 174 ( 2005), p. 399-406
    Abstract: A 1995 surge of Variegated Glacier, Alaska, USA, is discussed in the context of its six 20th-century predecessors, especially the previous surge in 1982/83 which was studied in detail. The average time between surge initiations is 15 years. The 1995 surge was considerably weaker than its predecessors, having a single phase or at most a very weak second phase. The 1995 surge confirms that there is a seasonal cycle, with surge initiation in winter and termination in the first part of the melt season, and a correlation between weather and both surge termination date and surge extent. Two days of record high temperature correlated with the termination of the 1995 surge. The most obvious issue is the absence of a strong second surge phase (as there was in the 1982/83 surge) culminating in a surge extent more in line with that of the predecessors. This is considered in the light of a simple criterion for surge initiation and re-initiation which depends upon the evolving basal shear stress.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.3189/172756505781829250
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2005
    detail.hit.zdb_id: 2140541-4
    SSG: 14
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Online Resource
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...