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  • 1
    Online-Ressource
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    Ice core evidence for a very tight link between North Atlantic and east Asian glacial climate
    American Geophysical Union (AGU) ; 2007
    In:  Geophysical Research Letters Vol. 34, No. 3 ( 2007-02-09)
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 34, No. 3 ( 2007-02-09)
    Materialart: Online-Ressource
    ISSN: 0094-8276
    URL: Article
    DOI: 10.1029/2006GL027876
    Sprache: Englisch
    Verlag: American Geophysical Union (AGU)
    Publikationsdatum: 2007
    ZDB Id: 2021599-X
    ZDB Id: 7403-2
    SSG: 16,13
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  • 2
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    Retrieval of Snow Properties from the Sentinel-3 Ocean and Land Colour Instrument
    MDPI AG ; 2019
    In:  Remote Sensing Vol. 11, No. 19 ( 2019-09-29), p. 2280-
    Details
    In: Remote Sensing, MDPI AG, Vol. 11, No. 19 ( 2019-09-29), p. 2280-
    Kurzfassung: The Sentinel Application Platform (SNAP) architecture facilitates Earth Observation data processing. In this work, we present results from a new Snow Processor for SNAP. We also describe physical principles behind the developed snow property retrieval technique based on the analysis of Ocean and Land Colour Instrument (OLCI) onboard Sentinel-3A/B measurements over clean and polluted snow fields. Using OLCI spectral reflectance measurements in the range 400–1020 nm, we derived important snow properties such as spectral and broadband albedo, snow specific surface area, snow extent and grain size on a spatial grid of 300 m. The algorithm also incorporated cloud screening and atmospheric correction procedures over snow surfaces. We present validation results using ground measurements from Antarctica, the Greenland ice sheet and the French Alps. We find the spectral albedo retrieved with accuracy of better than 3% on average, making our retrievals sufficient for a variety of applications. Broadband albedo is retrieved with the average accuracy of about 5% over snow. Therefore, the uncertainties of satellite retrievals are close to experimental errors of ground measurements. The retrieved surface grain size shows good agreement with ground observations. Snow specific surface area observations are also consistent with our OLCI retrievals. We present snow albedo and grain size mapping over the inland ice sheet of Greenland for areas including dry snow, melted/melting snow and impurity rich bare ice. The algorithm can be applied to OLCI Sentinel-3 measurements providing an opportunity for creation of long-term snow property records essential for climate monitoring and data assimilation studies—especially in the Arctic region, where we face rapid environmental changes including reduction of snow/ice extent and, therefore, planetary albedo.
    Materialart: Online-Ressource
    ISSN: 2072-4292
    URL: Article
    DOI: 10.3390/rs11192280
    Sprache: Englisch
    Verlag: MDPI AG
    Publikationsdatum: 2019
    ZDB Id: 2513863-7
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  • 3
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    Ice-core data used for the construction of the Greenland Ice-Core Chronology 2005 and 2021 (GICC05 and GICC21)
    Copernicus GmbH ; 2023
    In:  Earth System Science Data Vol. 15, No. 8 ( 2023-08-02), p. 3351-3364
    Details
    In: Earth System Science Data, Copernicus GmbH, Vol. 15, No. 8 ( 2023-08-02), p. 3351-3364
    Kurzfassung: Abstract. We here describe, document, and make available a wide range of data sets used for annual-layer identification in ice cores from DYE-3, GRIP, NGRIP, NEEM, and EGRIP. The data stem from detailed measurements performed both on the main deep cores and shallow cores over more than 40 years using many different setups developed by research groups in several countries and comprise both discrete measurements from cut ice samples and continuous-flow analysis data. The data series were used for counting annual layers 60 000 years back in time during the construction of the Greenland Ice-Core Chronology 2005 (GICC05) and/or the revised GICC21, which currently only reaches 3800 years back. Now that the underlying data are made available (listed in Table 1) we also release the individual annual-layer positions of the GICC05 timescale which are based on these data sets. We hope that the release of the data sets will stimulate further studies of the past climate taking advantage of these highly resolved data series covering a large part of the interior of the Greenland ice sheet.
    Materialart: Online-Ressource
    ISSN: 1866-3516
    URL: Article
    DOI: 10.5194/essd-15-3351-2023
    Sprache: Englisch
    Verlag: Copernicus GmbH
    Publikationsdatum: 2023
    ZDB Id: 2475469-9
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  • 4
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    Constraints on post-depositional isotope modifications in East Antarctic firn from analysing temporal changes of isotope profiles
    Copernicus GmbH ; 2017
    In:  The Cryosphere Vol. 11, No. 5 ( 2017-09-12), p. 2175-2188
    Details
    In: The Cryosphere, Copernicus GmbH, Vol. 11, No. 5 ( 2017-09-12), p. 2175-2188
    Kurzfassung: Abstract. The isotopic composition of water in ice sheets is extensively used to infer past climate changes. In low-accumulation regions their interpretation is, however, challenged by poorly constrained effects that may influence the initial isotope signal during and after deposition of the snow. This is reflected in snow-pit isotope data from Kohnen Station, Antarctica, which exhibit a seasonal cycle but also strong interannual variations that contradict local temperature observations. These inconsistencies persist even after averaging many profiles and are thus not explained by local stratigraphic noise. Previous studies have suggested that post-depositional processes may significantly influence the isotopic composition of East Antarctic firn. Here, we investigate the importance of post-depositional processes within the open-porous firn (≳ 10 cm depth) at Kohnen Station by separating spatial from temporal variability. To this end, we analyse 22 isotope profiles obtained from two snow trenches and examine the temporal isotope modifications by comparing the new data with published trench data extracted 2 years earlier. The initial isotope profiles undergo changes over time due to downward advection, firn diffusion and densification in magnitudes consistent with independent estimates. Beyond that, we find further modifications of the original isotope record to be unlikely or small in magnitude (≪ 1 ‰ RMSD). These results show that the discrepancy between local temperatures and isotopes most likely originates from spatially coherent processes prior to or during deposition, such as precipitation intermittency or systematic isotope modifications acting on drifting or loose surface snow.
    Materialart: Online-Ressource
    ISSN: 1994-0424
    URL: Article
    DOI: 10.5194/tc-11-2175-2017
    Sprache: Englisch
    Verlag: Copernicus GmbH
    Publikationsdatum: 2017
    ZDB Id: 2393169-3
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  • 5
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    EBSD analysis of subgrain boundaries and dislocation slip systems in Antarctic and Greenland ice
    Copernicus GmbH ; 2017
    In:  Solid Earth Vol. 8, No. 5 ( 2017-09-06), p. 883-898
    Details
    In: Solid Earth, Copernicus GmbH, Vol. 8, No. 5 ( 2017-09-06), p. 883-898
    Kurzfassung: Abstract. Ice has a very high plastic anisotropy with easy dislocation glide on basal planes, while glide on non-basal planes is much harder. Basal glide involves dislocations with the Burgers vector b = 〈a〉, while glide on non-basal planes can involve dislocations with b = 〈a〉, b = [c], and b = 〈c + a〉. During the natural ductile flow of polar ice sheets, most of the deformation is expected to occur by basal slip accommodated by other processes, including non-basal slip and grain boundary processes. However, the importance of different accommodating processes is controversial. The recent application of micro-diffraction analysis methods to ice, such as X-ray Laue diffraction and electron backscattered diffraction (EBSD), has demonstrated that subgrain boundaries indicative of non-basal slip are present in naturally deformed ice, although so far the available data sets are limited. In this study we present an analysis of a large number of subgrain boundaries in ice core samples from one depth level from two deep ice cores from Antarctica (EPICA-DML deep ice core at 656 m of depth) and Greenland (NEEM deep ice core at 719 m of depth). EBSD provides information for the characterization of subgrain boundary types and on the dislocations that are likely to be present along the boundary. EBSD analyses, in combination with light microscopy measurements, are presented and interpreted in terms of the dislocation slip systems. The most common subgrain boundaries are indicative of basal 〈a〉 slip with an almost equal occurrence of subgrain boundaries indicative of prism [c] or 〈c + a〉 slip on prism and/or pyramidal planes. A few subgrain boundaries are indicative of prism 〈a〉 slip or slip of 〈a〉 screw dislocations on the basal plane. In addition to these classical polygonization processes that involve the recovery of dislocations into boundaries, alternative mechanisms are discussed for the formation of subgrain boundaries that are not related to the crystallography of the host grain.The finding that subgrain boundaries indicative of non-basal slip are as frequent as those indicating basal slip is surprising. Our evidence of frequent non-basal slip in naturally deformed polar ice core samples has important implications for discussions on ice about plasticity descriptions, rate-controlling processes which accommodate basal glide, and anisotropic ice flow descriptions of large ice masses with the wider perspective of sea level evolution.
    Materialart: Online-Ressource
    ISSN: 1869-9529
    URL: Article
    DOI: 10.5194/se-8-883-2017
    Sprache: Englisch
    Verlag: Copernicus GmbH
    Publikationsdatum: 2017
    ZDB Id: 2545676-3
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  • 6
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    Distribution of air bubbles in the EDML and EDC (Antarctica) ice cores, using a new method of automatic image analysis
    International Glaciological Society ; 2010
    In:  Journal of Glaciology Vol. 56, No. 196 ( 2010), p. 339-348
    Details
    In: Journal of Glaciology, International Glaciological Society, Vol. 56, No. 196 ( 2010), p. 339-348
    Kurzfassung: Air bubbles in ice cores play an essential role in climate research, not only because they contain samples of the palaeoatmosphere, but also because their shape, size and distribution provide information about the past firn structure and the embedding of climate records into deep ice cores. In this context, we present profiles of average bubble size and bubble number for the entire EDML (Antarctica) core and the top 600 m of the EDC (Antarctica) core, and distributions of bubble sizes from selected depths. The data are generated with an image-processing framework which automatically extracts position, orientation, size and shape of an elliptical approximation of each bubble from thick-section micrographs, without user interaction. The presented software framework allows for registration of overlapping photomicrographs to yield accurate locations of bubble-like features. A comparison is made between the bubble parameterizations in the EDML and EDC cores and data published on the Vostok (Antarctica) ice core. The porosity at the firn/ice transition is inferred to lie between 8.62% and 10.48% for the EDC core and between 10.56% and 12.61 % for the EDML core.
    Materialart: Online-Ressource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.3189/002214310791968511
    Sprache: Englisch
    Verlag: International Glaciological Society
    Publikationsdatum: 2010
    ZDB Id: 2140541-4
    SSG: 14
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  • 7
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    The role of hydrochlorofluorocarbon densifiers in the formation of clathrate hydrates in deep boreholes and subglacial environments
    International Glaciological Society ; 2007
    In:  Annals of Glaciology Vol. 47 ( 2007), p. 109-114
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 47 ( 2007), p. 109-114
    Kurzfassung: Clear evidence for the formation of mixed clathrate hydrates of air and hydrochlorofluorocarbon densifier (known as HCFC-141b, sometimes also called R-141b) is found by means of synchrotron X-ray diffraction and Raman spectroscopy on a sample recovered from the bottom of the EPICA Dronning Maud Land deep borehole in Antarctica. Subglacial water (SGW) appears to have reacted with the drilling liquid to build a large lump of clathrate hydrate. The hydrate growth may well have been accelerated by the stirring of the SGW–densifier mixture during drilling. Moreover, dissolved air in the SGW appears to have participated in the formation of mixed hydrates of air and HCFC-141b as evidenced by the concomitant appearance of Raman signals from both constituents. Our findings elucidate to some extent the meaning of earlier accounts of the formation of ‘heavy chips’ that may sink to the bottom of the borehole, possibly affecting or even impeding the drilling advance. These observations raise concerns with respect to the use of HCFC-141b densifiers in ice-core drilling liquids under warm ice conditions.
    Materialart: Online-Ressource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.3189/172756407786857659
    Sprache: Englisch
    Verlag: International Glaciological Society
    Publikationsdatum: 2007
    ZDB Id: 2122400-6
    SSG: 14
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  • 8
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    Microstructure mapping: a new method for imaging deformation-induced microstructural features of ice on the grain scale
    International Glaciological Society ; 2006
    In:  Journal of Glaciology Vol. 52, No. 178 ( 2006), p. 398-406
    Details
    In: Journal of Glaciology, International Glaciological Society, Vol. 52, No. 178 ( 2006), p. 398-406
    Kurzfassung: This work presents a method of mapping deformation-related sublimation patterns, formed on the surface of ice specimens, at microscopic resolution (3–4 μm pixel −1 ). The method is based on the systematic sublimation of a microtomed piece of ice, prepared either as a thick or a thin section. The mapping system consists of an optical microscope, a CCD video camera and a computer-controlled xy -stage. About 1500 images are needed to build a high-resolution mosaic map of a 4.5 × 9 cm section. Mosaics and single images are used to derive a variety of statistical data about air inclusions (air bubbles and air clathrate hydrates), texture (grain size, shape and orientation) and deformation-related features (subgrain boundaries, slip bands, subgrain islands and loops, pinned and bulged grain boundaries). The most common sublimation patterns are described, and their relevance for the deformation of polar ice is briefly discussed.
    Materialart: Online-Ressource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.3189/172756506781828647
    Sprache: Englisch
    Verlag: International Glaciological Society
    Publikationsdatum: 2006
    ZDB Id: 2140541-4
    SSG: 14
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  • 9
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    High-resolution variations in size, number and arrangement of air bubbles in the EPICA DML (Antarctica) ice core
    International Glaciological Society ; 2013
    In:  Journal of Glaciology Vol. 59, No. 217 ( 2013), p. 972-980
    Details
    In: Journal of Glaciology, International Glaciological Society, Vol. 59, No. 217 ( 2013), p. 972-980
    Kurzfassung: We investigated the large-scale (10–1000 m) and small-scale (mm–cm) variations in size, number and arrangement of air bubbles in the EPICA Dronning Maud Land (EDML) (Antarctica) ice core, down to the end of the bubble/hydrate transition (BHT) zone. On the large scale, the bubble number density shows a general correlation with the palaeo-temperature proxy, δ 18 O, and the dust concentration, which means that in Holocene ice there are fewer bubbles than in glacial ice. Small-scale variations in bubble number and size were identified and compared. Above the BHT zone there exists a strong anticorrelation between bubble number density and mean bubble size. In glacial ice, layers of high number density and small bubble size are linked with layers with high impurity content, identified as cloudy bands. Therefore, we regard impurities as a controlling factor for the formation and distribution of bubbles in glacial ice. The anticorrelation inverts in the middle of the BHT zone. In the lower part of the BHT zone, bubble-free layers exist that are also associated with cloudy bands. The high contrast in bubble number density in glacial ice, induced by the impurities, indicates a much more pronounced layering in glacial firn than in modern firn.
    Materialart: Online-Ressource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.3189/2013JoG12J245
    Sprache: Englisch
    Verlag: International Glaciological Society
    Publikationsdatum: 2013
    ZDB Id: 2140541-4
    SSG: 14
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  • 10
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    Raman tomography of natural air hydrates
    International Glaciological Society ; 2015
    In:  Journal of Glaciology Vol. 61, No. 229 ( 2015), p. 923-930
    Details
    In: Journal of Glaciology, International Glaciological Society, Vol. 61, No. 229 ( 2015), p. 923-930
    Kurzfassung: Cryo-Raman tomography allows us, for the first time, to determine accurate morphologies and volumes of natural air hydrates in Antarctic ice cores. The measurements show complex growth structures that are not accounted for by the available models of hydrate formation.
    Materialart: Online-Ressource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.3189/2015JoG15J009
    Sprache: Englisch
    Verlag: International Glaciological Society
    Publikationsdatum: 2015
    ZDB Id: 2140541-4
    SSG: 14
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