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  • 1
    Online Resource
    Online Resource
    Evidence of Cascading Subglacial Water Flow at Jutulstraumen Glacier (Antarctica) Derived From Sentinel‐1 and ICESat‐2 Measurements
    American Geophysical Union (AGU) ; 2021
    In:  Geophysical Research Letters Vol. 48, No. 20 ( 2021-10-28)
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 48, No. 20 ( 2021-10-28)
    Abstract: Sentinel‐1 DInSAR estimates reveal a ∼175 km flow path of a cascade‐like chain of subglacial water propagation over a 1‐year period High‐resolution ultra‐wideband radar data show no characteristic lake bed reflections and suggests water transport via a local trough system We find evidence of highly dynamic water transport in a static glacial stetting providing a benchmark dataset to improve modeling results
    Type of Medium: Online Resource
    ISSN: 0094-8276 , 1944-8007
    URL: Article
    DOI: 10.1029/2021GL094472
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2021
    detail.hit.zdb_id: 2021599-X
    detail.hit.zdb_id: 7403-2
    SSG: 16,13
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  • 2
    Online Resource
    Online Resource
    Surface Melting Drives Fluctuations in Airborne Radar Penetration in West Central Greenland
    American Geophysical Union (AGU) ; 2020
    In:  Geophysical Research Letters Vol. 47, No. 17 ( 2020-09-16)
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 47, No. 17 ( 2020-09-16)
    Abstract: We use airborne radar, firn cores, and firn models to confirm that summer melting is the principal source of radar penetration fluctuations The largest fluctuations are recorded after the extreme melt event of 2012, which caused a 6.2 ± 2.4 m reduction in radar penetration Echo retracking compensates for radar penetration fluctuations, leading to surface heights that agree with laser data to within 13.9 cm
    Type of Medium: Online Resource
    ISSN: 0094-8276 , 1944-8007
    URL: Article
    DOI: 10.1029/2020GL088293
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2020
    detail.hit.zdb_id: 2021599-X
    detail.hit.zdb_id: 7403-2
    SSG: 16,13
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  • 3
    Online Resource
    Online Resource
    On the link between surface and basal structures of the Jelbart Ice Shelf, Antarctica
    International Glaciological Society ; 2015
    In:  Journal of Glaciology Vol. 61, No. 229 ( 2015), p. 975-986
    Details
    In: Journal of Glaciology, International Glaciological Society, Vol. 61, No. 229 ( 2015), p. 975-986
    Abstract: To understand the dynamics of ice shelves, a knowledge of their internal and basal structure is very important. As the capacity to perform local surveys is limited, remote sensing provides an opportunity to obtain the relevant information. We must prove, however, that the relevant information can be obtained from remote sensing of the surface. That is the aim of this study. The Jelbart Ice Shelf, Antarctica, exhibits a variety of surface structures appearing as stripe-like features in radar imagery. We performed an airborne geophysical survey across these features and compared the results to TerraSAR-X imagery. We find that the stripe-like structures indicate surface troughs coinciding with the location of basal channels and crevasse-like features, revealed by radio-echo sounding. HH and VV polarizations do not show different magnitude. In surface troughs, the local accumulation rate is larger than at the flat surface. Viscoelastic modelling is used to gain an understanding of the surface undulations and their origin. The surface displacement, computed with a Maxwell model, matches the observed surface reasonably well. Our simulations show that the surface troughs develop over decadal to centennial timescales.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.3189/2015JoG15J023
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2015
    detail.hit.zdb_id: 2140541-4
    SSG: 14
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  • 4
    Online Resource
    Online Resource
    Greenland annual accumulation along the EGIG line, 1959–2004, from ASIRAS airborne radar and neutron-probe density measurements
    Copernicus GmbH ; 2016
    In:  The Cryosphere Vol. 10, No. 4 ( 2016-08-02), p. 1679-1694
    Details
    In: The Cryosphere, Copernicus GmbH, Vol. 10, No. 4 ( 2016-08-02), p. 1679-1694
    Abstract: Abstract. We report annual snow accumulation rates from 1959 to 2004 along a 250 km segment of the Expéditions Glaciologiques Internationales au Groenland (EGIG) line across central Greenland using Airborne SAR/Interferometric Radar Altimeter System (ASIRAS) radar layers and high resolution neutron-probe (NP) density profiles. ASIRAS-NP-derived accumulation rates are not statistically different (95 % confidence interval) from in situ EGIG accumulation measurements from 1985 to 2004. ASIRAS-NP-derived accumulation increases by 20 % below 3000 m elevation, and increases by 13 % above 3000 m elevation for the period 1995 to 2004 compared to 1985 to 1994. Three Regional Climate Models (PolarMM5, RACMO2.3, MAR) underestimate snow accumulation below 3000 m by 16–20 % compared to ASIRAS-NP from 1985 to 2004. We test radar-derived accumulation rates sensitivity to density using modeled density profiles in place of NP densities. ASIRAS radar layers combined with Herron and Langway (1980) model density profiles (ASIRAS-HL) produce accumulation rates within 3.5 % of ASIRAS-NP estimates in the dry snow region. We suggest using Herron and Langway (1980) density profiles to calibrate radar layers detected in dry snow regions of ice sheets lacking detailed in situ density measurements, such as those observed by the Operation IceBridge campaign.
    Type of Medium: Online Resource
    ISSN: 1994-0424
    URL: Article
    DOI: 10.5194/tc-10-1679-2016
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2016
    detail.hit.zdb_id: 2393169-3
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  • 5
    Online Resource
    Online Resource
    On the evolution of an ice shelf melt channel at the base of Filchner Ice Shelf, from observations and viscoelastic modeling
    Copernicus GmbH ; 2022
    In:  The Cryosphere Vol. 16, No. 10 ( 2022-10-10), p. 4107-4139
    Details
    In: The Cryosphere, Copernicus GmbH, Vol. 16, No. 10 ( 2022-10-10), p. 4107-4139
    Abstract: Abstract. Ice shelves play a key role in the stability of the Antarctic Ice Sheet due to their buttressing effect. A loss of buttressing as a result of increased basal melting or ice shelf disintegration will lead to increased ice discharge. Some ice shelves exhibit channels at the base that are not yet fully understood. In this study, we present in situ melt rates of a channel which is up to 330 m high and located in the southern Filchner Ice Shelf. Maximum observed melt rates are 2 m yr−1. Melt rates inside the channel decrease in the direction of ice flow and turn to freezing ∼55 km downstream of the grounding line. While closer to the grounding line melt rates are higher within the channel than outside, this relationship reverses further downstream. Comparing the modeled evolution of this channel under present-day climate conditions over 250 years with its present geometry reveals a mismatch. Melt rates twice as large as the present-day values are required to fit the observed geometry. In contrast, forcing the model with present-day melt rates results in a closure of the channel, which contradicts observations. The ice shelf experiences strong tidal variability in vertical strain rates at the measured site, and discrete pulses of increased melting occurred throughout the measurement period. The type of melt channel in this study diminishes in height with distance from the grounding line and is hence not a destabilizing factor for ice shelves.
    Type of Medium: Online Resource
    ISSN: 1994-0424
    URL: Article
    DOI: 10.5194/tc-16-4107-2022
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2022
    detail.hit.zdb_id: 2393169-3
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  • 6
    Online Resource
    Online Resource
    About the consistency between Envisat and CryoSat-2 radar freeboard retrieval over Antarctic sea ice
    Copernicus GmbH ; 2016
    In:  The Cryosphere Vol. 10, No. 4 ( 2016-07-08), p. 1415-1425
    Details
    In: The Cryosphere, Copernicus GmbH, Vol. 10, No. 4 ( 2016-07-08), p. 1415-1425
    Abstract: Abstract. Knowledge about Antarctic sea-ice volume and its changes over the past decades has been sparse due to the lack of systematic sea-ice thickness measurements in this remote area. Recently, first attempts have been made to develop a sea-ice thickness product over the Southern Ocean from space-borne radar altimetry and results look promising. Today, more than 20 years of radar altimeter data are potentially available for such products. However, the characteristics of individual radar types differ for the available altimeter missions. Hence, it is important and our goal to study the consistency between single sensors in order to develop long and consistent time series. Here, the consistency between freeboard measurements of the Radar Altimeter 2 on board Envisat and freeboard measurements from the Synthetic-Aperture Interferometric Radar Altimeter on board CryoSat-2 is tested for their overlap period in 2011. Results indicate that mean and modal values are in reasonable agreement over the sea-ice growth season (May–October) and partly also beyond. In general, Envisat data show higher freeboards in the first-year ice zone while CryoSat-2 freeboards are higher in the multiyear ice zone and near the coasts. This has consequences for the agreement in individual sectors of the Southern Ocean, where one or the other ice class may dominate. Nevertheless, over the growth season, mean freeboard for the entire (regionally separated) Southern Ocean differs generally by not more than 3 cm (8 cm, with few exceptions) between Envisat and CryoSat-2, and the differences between modal freeboards lie generally within ±10 cm and often even below.
    Type of Medium: Online Resource
    ISSN: 1994-0424
    URL: Article
    DOI: 10.5194/tc-10-1415-2016
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2016
    detail.hit.zdb_id: 2393169-3
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  • 7
    Online Resource
    Online Resource
    Glaciological characteristics in the Dome Fuji region and new assessment for “Oldest Ice”
    Copernicus GmbH ; 2018
    In:  The Cryosphere Vol. 12, No. 7 ( 2018-07-25), p. 2413-2424
    Details
    In: The Cryosphere, Copernicus GmbH, Vol. 12, No. 7 ( 2018-07-25), p. 2413-2424
    Abstract: Abstract. A key objective in palaeo-climatology is the retrieval of a continuous Antarctic ice-core record dating back 1.5 Ma. The identification of a suitable Antarctic site requires sufficient knowledge of the subglacial landscape beneath the Antarctic Ice Sheet. Here, we present new ice thickness information from the Dome Fuji region, East Antarctica, based on airborne radar surveys conducted during the 2014/15 and 2016/17 southern summers. Compared to previous maps of the region, the new dataset shows a more complex landscape with networks of valleys and mountain plateaus. We use the new dataset as input in a thermokinematic model that incorporates uncertainties in geothermal heat flux values in order to improve the predictions of potential ice-core sites. Our results show that especially the region immediately south of Dome Fuji station persists as a good candidate site for obtaining an old ice core. An initial assessment of basal conditions revealed the existence of what appears to be subglacial lakes. Further radar data analysis shows overall high continuity of layer stratigraphy in the region. This indicates that extending the age–depth information from the Dome Fuji ice core to a new ice-core drill site is a viable option.
    Type of Medium: Online Resource
    ISSN: 1994-0424
    URL: Article
    URL: Article
    DOI: 10.5194/tc-12-2413-2018
    DOI: 10.5194/tc-12-2413-2018-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2018
    detail.hit.zdb_id: 2393169-3
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  • 8
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    Online Resource
    Parameterizing anisotropic reflectance of snow surfaces from airborne digital camera observations in Antarctica
    Copernicus GmbH ; 2020
    In:  The Cryosphere Vol. 14, No. 11 ( 2020-11-12), p. 3959-3978
    Details
    In: The Cryosphere, Copernicus GmbH, Vol. 14, No. 11 ( 2020-11-12), p. 3959-3978
    Abstract: Abstract. The surface reflection of solar radiation comprises an important boundary condition for solar radiative transfer simulations. In polar regions above snow surfaces, the surface reflection is particularly anisotropic due to low Sun elevations and the highly anisotropic scattering phase function of the snow crystals. The characterization of this surface reflection anisotropy is essential for satellite remote sensing over both the Arctic and Antarctica. To quantify the angular snow reflection properties, the hemispherical-directional reflectance factor (HDRF) of snow surfaces was derived from airborne measurements in Antarctica during austral summer in 2013/14. For this purpose, a digital 180∘ fish-eye camera (green channel, 490–585 nm wavelength band) was used. The HDRF was measured for different surface roughness conditions, optical-equivalent snow grain sizes, and solar zenith angles. The airborne observations covered an area of around 1000 km × 1000 km in the vicinity of Kohnen Station (75∘0′ S, 0∘4′ E) at the outer part of the East Antarctic Plateau. The observations include regions with higher (coastal areas) and lower (inner Antarctica) precipitation amounts and frequencies. The digital camera provided upward, angular-dependent radiance measurements from the lower hemisphere. The comparison of the measured HDRF derived for smooth and rough snow surfaces (sastrugi) showed significant differences, which are superimposed on the diurnal cycle. By inverting a semi-empirical kernel-driven bidirectional reflectance distribution function (BRDF) model, the measured HDRF of snow surfaces was parameterized as a function of solar zenith angle, surface roughness, and optical-equivalent snow grain size. This allows a direct comparison of the HDRF measurements with the BRDF derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite product MCD43. For the analyzed cases, MODIS observations (545–565 nm wavelength band) generally underestimated the anisotropy of the surface reflection. The largest deviations were found for the volumetric model weight fvol (average underestimation by a factor of 10). These deviations are likely linked to short-term changes in snow properties.
    Type of Medium: Online Resource
    ISSN: 1994-0424
    URL: Article
    DOI: 10.5194/tc-14-3959-2020
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2020
    detail.hit.zdb_id: 2393169-3
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  • 9
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    Online Resource
    Direct measurement of warm Atlantic Intermediate Water close to the grounding line of Nioghalvfjerdsfjorden (79° N) Glacier, northeast Greenland
    Copernicus GmbH ; 2023
    In:  The Cryosphere Vol. 17, No. 5 ( 2023-05-05), p. 1821-1837
    Details
    In: The Cryosphere, Copernicus GmbH, Vol. 17, No. 5 ( 2023-05-05), p. 1821-1837
    Abstract: Abstract. The Northeast Greenland Ice Stream has recently seen significant change to its floating margins and has been identified as vulnerable to future climate warming. Inflow of warm Atlantic Intermediate Water (AIW) from the continental shelf has been observed in the vicinity of the Nioghalvfjerdsfjorden (79∘ N) Glacier calving front, but AIW penetration deep into the ice shelf cavity has not been observed directly. Here, we report temperature and salinity measurements from profiles in an epishelf lake, which provide the first direct evidence of AIW proximal to the grounding line of 79∘ N Glacier, over 50 km from the calving front. We also report evidence for partial un-grounding of the margin of 79∘ N Glacier taking place at the western end of the epishelf lake. Comparison of our measurements to those close to the calving front shows that AIW transits the cavity to reach the grounding line within a few months. The observations provide support for modelling studies that infer AIW-driven basal melt proximal to the grounding line and demonstrate that offshore oceanographic changes can be rapidly transmitted throughout the sub-ice-shelf cavity, with implications for near-future stability of the ice stream.
    Type of Medium: Online Resource
    ISSN: 1994-0424
    URL: Article
    DOI: 10.5194/tc-17-1821-2023
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2023
    detail.hit.zdb_id: 2393169-3
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  • 10
    Online Resource
    Online Resource
    Centennial response of Greenland’s three largest outlet glaciers
    Springer Science and Business Media LLC ; 2020
    In:  Nature Communications Vol. 11, No. 1 ( 2020-11-17)
    Details
    In: Nature Communications, Springer Science and Business Media LLC, Vol. 11, No. 1 ( 2020-11-17)
    Abstract: The Greenland Ice Sheet is the largest land ice contributor to sea level rise. This will continue in the future but at an uncertain rate and observational estimates are limited to the last few decades. Understanding the long-term glacier response to external forcing is key to improving projections. Here we use historical photographs to calculate ice loss from 1880–2012 for Jakobshavn, Helheim, and Kangerlussuaq glacier. We estimate ice loss corresponding to a sea level rise of 8.1 ± 1.1 millimetres from these three glaciers. Projections of mass loss for these glaciers, using the worst-case scenario, Representative Concentration Pathways 8.5, suggest a sea level contribution of 9.1–14.9 mm by 2100. RCP8.5 implies an additional global temperature increase of 3.7 °C by 2100, approximately four times larger than that which has taken place since 1880. We infer that projections forced by RCP8.5 underestimate glacier mass loss which could exceed this worst-case scenario.
    Type of Medium: Online Resource
    ISSN: 2041-1723
    URL: Article
    DOI: 10.1038/s41467-020-19580-5
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2020
    detail.hit.zdb_id: 2553671-0
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