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  • 1
    Online Resource
    Online Resource
    Cambridge University Press (CUP) ; 2017
    In:  Journal of Glaciology Vol. 63, No. 239 ( 2017-06), p. 556-564
    In: Journal of Glaciology, Cambridge University Press (CUP), Vol. 63, No. 239 ( 2017-06), p. 556-564
    Abstract: Ice-stream dynamics are strongly controlled by processes taking place at the ice/bed interface where subglacial water both lubricates the base and saturates any existing, underlying sediment. Large parts of the former Eurasian ice sheet were underlain by thick sequences of soft, marine sediments and many areas are imprinted with geomorphological features indicative of fast flow and wet basal conditions. Here, we study the effect of subglacial water on past Eurasian ice-sheet dynamics by incorporating a thin-film model of basal water flow into the ice-sheet model SICOPOLIS and use it to better represent flow in temperate areas. The adjunction of subglacial hydrology results in a smaller ice-sheet building up over time and generally faster ice velocities, which consequently reduces the total area fraction of temperate basal ice and ice streaming areas. Minima in the hydraulic pressure potential, governing water flow, are used as indicators for potential locations of past subglacial lakes and a probability distribution of lake existence is presented based on estimated lake depth and longevity.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2017
    detail.hit.zdb_id: 2140541-4
    SSG: 14
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  • 2
    Online Resource
    Online Resource
    Cambridge University Press (CUP) ; 2020
    In:  Annals of Glaciology Vol. 61, No. 81 ( 2020-04), p. 162-175
    In: Annals of Glaciology, Cambridge University Press (CUP), Vol. 61, No. 81 ( 2020-04), p. 162-175
    Abstract: Basal motion of ice sheets depends in part on the roughness and material properties of the subglacial bed and the occurrence of water. To date, basal motion represents one of the largest uncertainties in ice-flow models. It is that component of the total flow velocity that can change most rapidly and can, therefore, facilitate rapid variations in dynamic behaviour. In this study, we investigate the subglacial properties of the East Antarctic Ice Sheet by statistically analysing the roughness of the bed topography, inferred from radio-echo sounding measurements. We analyse two sets of roughness parameters, one derived in the spatial and the other in the spectral domain, with two roughness parameters each. This enables us to compare the suitability of the four roughness parameters to classify the subglacial landscapes below the ice sheet. We further investigate the relationship of the roughness parameters with observed surface flow velocity and modelled basal temperatures of the ice sheet. We find that one of the roughness parameters, the Hurst exponent derived in the spatial domain, coincides with the thermal condition at the base of the ice sheet for slow flow velocities and varies with flow velocity.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2020
    detail.hit.zdb_id: 2122400-6
    SSG: 14
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  • 3
    Online Resource
    Online Resource
    Cambridge University Press (CUP) ; 2019
    In:  Journal of Glaciology Vol. 65, No. 250 ( 2019-04), p. 212-224
    In: Journal of Glaciology, Cambridge University Press (CUP), Vol. 65, No. 250 ( 2019-04), p. 212-224
    Abstract: In the current ice-sheet models calving of ice shelves is based on phenomenological approaches. To obtain physics-based calving criteria, a viscoelastic Maxwell model is required accounting for short-term elastic and long-term viscous deformation. On timescales of months to years between calving events, as well as on long timescales with several subsequent iceberg break-offs, deformations are no longer small and linearized strain measures cannot be used. We present a finite deformation framework of viscoelasticity and extend this model by a nonlinear Glen-type viscosity. A finite element implementation is used to compute stress and strain states in the vicinity of the ice-shelf calving front. Stress and strain maxima of small (linearized strain measure) and finite strain formulations differ by ~ 5% after 1 and by ~ 30% after 10 years, respectively. A finite deformation formulation reaches a critical stress or strain faster, thus calving rates will be higher, despite the fact that the exact critical values are not known. Nonlinear viscosity of Glen-type leads to higher stress values. The Maxwell material model formulation for finite deformations presented here can also be applied to other glaciological problems, for example, tidal forcing at grounding lines or closure of englacial and subglacial melt channels.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2019
    detail.hit.zdb_id: 2140541-4
    SSG: 14
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  • 4
    In: Journal of Glaciology, Cambridge University Press (CUP), Vol. 66, No. 260 ( 2020-12), p. 891-904
    Abstract: Antarctica's ice shelves modulate the grounded ice flow, and weakening of ice shelves due to climate forcing will decrease their ‘buttressing’ effect, causing a response in the grounded ice. While the processes governing ice-shelf weakening are complex, uncertainties in the response of the grounded ice sheet are also difficult to assess. The Antarctic BUttressing Model Intercomparison Project (ABUMIP) compares ice-sheet model responses to decrease in buttressing by investigating the ‘end-member’ scenario of total and sustained loss of ice shelves. Although unrealistic, this scenario enables gauging the sensitivity of an ensemble of 15 ice-sheet models to a total loss of buttressing, hence exhibiting the full potential of marine ice-sheet instability. All models predict that this scenario leads to multi-metre (1–12 m) sea-level rise over 500 years from present day. West Antarctic ice sheet collapse alone leads to a 1.91–5.08 m sea-level rise due to the marine ice-sheet instability. Mass loss rates are a strong function of the sliding/friction law, with plastic laws cause a further destabilization of the Aurora and Wilkes Subglacial Basins, East Antarctica. Improvements to marine ice-sheet models have greatly reduced variability between modelled ice-sheet responses to extreme ice-shelf loss, e.g. compared to the SeaRISE assessments.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2020
    detail.hit.zdb_id: 2140541-4
    SSG: 14
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  • 5
    In: Polar Record, Cambridge University Press (CUP), Vol. 51, No. 6 ( 2015-11), p. 590-610
    Abstract: The German Antarctic Receiving Station (GARS) O’Higgins at the northern tip of the Antarctic Peninsula is a dual purpose facility for earth observation and has existed for more than 20 years. It serves as a satellite ground station for payload data downlink and telecommanding of remote sensing satellites as well as a geodetic observatory for global reference systems and global change. Both applications use the same 9 m diameter radio antenna. Major outcomes of this usage are summarised in this paper. The satellite ground station O’Higgins (OHG) is part of the global ground station network of the German Remote Sensing Data Centre (DFD) operated by the German Aerospace Centre (DLR). It was established in 1991 to provide remote sensing data downlink support within the missions of the European Remote Sensing Satellites ERS-1 and ERS-2. These missions provided valuable insights into the changes of the Antarctic ice shield. Especially after the failure of the on-board data recorder, OHG became an essential downlink station for ERS-2 real-time data transmission. Since 2010, OHG is manned during the entire year, specifically to support the TanDEM-X mission. OHG is a main dump station for payload data, monitoring and telecommanding of the German TerraSAR-X and TanDEM-X satellites. For space geodesy and astrometry the radio antenna O’Higgins significantly improves coverage over the southern hemisphere and plays an essential role within the global Very Long Baseline Interferometry (VLBI) network. In particular the determination of the Earth Orientation Parameters (EOP) and the sky coverage of the International Celestial Reference Frame (ICRF) benefit from the location at a high southern latitude. Further, the resolution of VLBI images of active galactic nuclei (AGN), cosmic radio sources defining the ICRF, improves significantly when O’Higgins is included in the network. The various geodetic instrumentation and the long time series at O’Higgins allow a reliable determination of crustal motions. VLBI station velocities, continuous GNSS measurements and campaign-wise absolute gravity measurements consistently document a vertical rate of about 5 mm/a. This crustal uplift is interpreted as an elastic rebound due to ice loss as a consequence of the ice shelf disintegration in the Prince Gustav Channel in the late 1990s. The outstanding location on the Antarctic continent and its year-around operation make GARS O’Higgins in future increasingly attractive for polar orbiting satellite missions and a vitally important station for the global VLBI network. Future plans call for the development of an observatory for environmentally relevant research. That means that the portfolio of the station will be expanded including the expansion of the infrastructure and the construction and operation of new scientific instruments suitable for long-term measurements and satellite ground truthing.
    Type of Medium: Online Resource
    ISSN: 0032-2474 , 1475-3057
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2015
    detail.hit.zdb_id: 3926-3
    detail.hit.zdb_id: 2100301-4
    SSG: 14
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