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  • 1
    Online Resource
    Online Resource
    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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    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
    SSG: 14
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  • 3
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    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
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  • 4
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    Online Resource
    Past and present accumulation rate reconstruction along the Dome Fuji–Kohnen radio-echo sounding profile, Dronning Maud Land, East Antarctica
    International Glaciological Society ; 2009
    In:  Annals of Glaciology Vol. 50, No. 51 ( 2009), p. 112-120
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 50, No. 51 ( 2009), p. 112-120
    Abstract: We used internal ice layers from a radio-echo sounding profile between the Kohnen and Dome Fuji deep drilling sites to infer the spatio-temporal pattern of accumulation rate in this sector of Dronning Maud Land, East Antarctica. Continuous internal reflection horizons can be traced to about half of the ice thickness and have a maximum age of approximately 72.7 ka BP. To infer palaeo-accumulation rates from the dated layers, we derived the thinning functions from a flow calculation with a high-resolution higher-order model of Dronning Maud Land embedded into a three-dimensional thermomechanical model of the Antarctic ice sheet. The method takes into account complex ice-flow dynamics and advection effects that cannot be dealt with using traditional local approaches. We selected seven time intervals over which we determine the average accumulation rate and average surface temperature at the place and time of origin of the layer particles. Our results show lower accumulation rates along eastern parts of the profile for the late Holocene (0–5 ka BP) than are shown by existing maps, which had no surface control points. During the last glacial period we find a substantially lower accumulation rate than predicted by the usual approach linking palaeo-accumulation rates to the condensation temperature above the surface inversion layer. These findings were used to fine-tune the relation between accumulation rate and temperature.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.3189/172756409789097513
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2009
    detail.hit.zdb_id: 2122400-6
    SSG: 14
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  • 5
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    Online Resource
    Real‐time underwater sounds from the Southern Ocean
    American Geophysical Union (AGU) ; 2006
    In:  Eos, Transactions American Geophysical Union Vol. 87, No. 36 ( 2006-09-05), p. 361-361
    Details
    In: Eos, Transactions American Geophysical Union, American Geophysical Union (AGU), Vol. 87, No. 36 ( 2006-09-05), p. 361-361
    Abstract: Marine sound, natural or anthropogenic, has long fascinated scientists, mariners, and the general public. The haunting songs of humpback whales and the pings of antisubmarine sonar, among other sounds from the oceans, convey allure and suspense. Recently, that suspense has moved from television screens to courtrooms, where navies, scientists, and environmentalists have clashed over the effects of anthropogenic sound on marine mammals [ Malakoff , 2002]. Triggered by atypical mass strandings of primarily beaked whales in concordance with naval sonar exercises off Greece in 1996 and the Bahamas in 2000, substantial efforts to obtain baseline data to understand the possible effects of anthropogenic sound on marine mammals have commenced. Recent advances include dive and vocalization records of beaked whales [ Johnson et al ., 2004] and detailed observations of the behavioral response of sperm whales on seismic signals [ Jochens et al ., 2006].
    Type of Medium: Online Resource
    ISSN: 0096-3941 , 2324-9250
    URL: Article
    DOI: 10.1029/2006EO360002
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2006
    detail.hit.zdb_id: 24845-9
    detail.hit.zdb_id: 2118760-5
    detail.hit.zdb_id: 240154-X
    SSG: 16,13
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  • 6
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    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
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  • 7
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    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
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  • 8
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    Regional and temporal variation of accumulation around NorthGRIP derived from ground-penetrating radar
    International Glaciological Society ; 2005
    In:  Annals of Glaciology Vol. 42 ( 2005), p. 326-330
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 42 ( 2005), p. 326-330
    Abstract: During the summer of 2003, a ground-penetrating radar survey around the North Greenland Icecore Project (NorthGRIP) deep ice-core drilling site (75˚06’N, 42˚20’W; 2957ma.s.l.) was carried out using a shielded 250 MHz radar system. The drill site is located on an ice divide, roughly 300 km north-northwest of the summit of the Greenland ice sheet. More than 430 km of profiles were measured, covering a 10 km by 10 km area, with a grid centered on the drilling location, and eight profiles extending beyond this grid. Seven internal horizons within the upper 120 m of the ice sheet were continuously tracked, containing the last 400 years of accumulation history. Based on the age-depth and density-depth distribution of the deep core, the internal layers have been dated and the regional and temporal distribution of accumulation rate in the vicinity of NorthGRIP has been derived. The distribution of accumulation shows a relatively smoothly increasing trend from east to west from 145 kgm –2 a– 1 to 200 kg m –2 a -1 over a distance of 50 km across the ice divide. The general trend is overlain by small-scale variations on the order of 2.5 kgm –2 a -1 km - 1 , i.e. around 1.5% of the accumulation mean. The temporal variations of the seven periods defined by the seven tracked isochrones are on the order of ± 4% of the mean of the last 400 years, i.e. at NorthGRIP ± 7 kg m –2 a -1 . If the regional accumulation pattern has been stable for the last several thousand years during the Holocene, and ice flow has been comparable to today, advective effects along the particle trajectory upstream of NorthGRIP do not have a significant effect on the interpretation of climatically induced changes in accumulation rates derived from the deep ice core over the last 10 kyr.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.3189/172756405781812574
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2005
    detail.hit.zdb_id: 2122400-6
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  • 9
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    Nivlisen, an Antarctic ice shelf in Dronning Maud Land: geodetic–glaciological results from a combined analysis of ice thickness, ice surface height and ice-flow observations
    International Glaciological Society ; 2006
    In:  Journal of Glaciology Vol. 52, No. 176 ( 2006), p. 17-30
    Details
    In: Journal of Glaciology, International Glaciological Society, Vol. 52, No. 176 ( 2006), p. 17-30
    Abstract: Extensive observations on Nivlisen, an ice shelf on Antarctica’s Atlantic coast, are analyzed and combined to obtain a new description of its complex glaciological regime. We generate models of ice thickness (primarily from ground-penetrating radar), ellipsoidal ice surface height (primarily from ERS-1 satellite altimetry), freeboard height (by utilizing precise sea surface information) and ice-flow velocity (from ERS-1/-2 SAR interferometry and GPS measurements). Accuracy assessments are included. Exploiting the hydrostatic equilibrium relation, we infer the ‘apparent air layer thickness’ as a useful measure for a glacier’s density deviation from a pure ice body. This parameter exhibits a distinct spatial variation (ranging from ≈2 to ≈16m) which we attribute to the transition from an ablation area to an accumulation area. We compute mass-flux and mass-balance parameters on a local and areally integrated scale. The combined effect of bottom mass balance and temporal change averaged over an essential part of Nivlisen is –654 ± 170 kg m –2 a –1 , which suggests bottom melting processes dominate. We discuss our results in view of temporal ice-mass changes (including remarks on historical observations), basal processes, near-surface processes and ice-flow dynamical features. The question of temporal changes remains open from the data at hand, and we recommend further observations and analyses for its solution.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.3189/172756506781828953
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2006
    detail.hit.zdb_id: 2140541-4
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