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  • 1
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    Online Resource
    The response of the Greenland ice sheet to climate changes in the 21st century by interactive coupling of an AOGCM with a thermomechanical ice-sheet model
    International Glaciological Society ; 2002
    In:  Annals of Glaciology Vol. 35 ( 2002), p. 409-415
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 35 ( 2002), p. 409-415
    Abstract: We present results from a greenhouse warming experiment obtained from an atmosphere–ocean–sea-ice general circulation model that is interactively coupled with a three-dimensional model of the Greenland ice sheet. the experiment covers the period 1970–2099 and is driven by the mid-range Intergovernmental Panel on Climate Change SRESB2 scenario. the Greenland model is a thermomechanical high-resolution (20 km) model coupled with a viscoelastic bedrock model. the melt-and-runoff model is based on the positive degree-day method and includes meltwater retention in the snowpack and the formation of superimposed ice. the atmospheric–oceanic general circulation model (AOGCM) is a coarse-resolution model without flux correction based on the Laboratoire de Météorologie Dynamique (Paris) LMD 5.3 atmospheric model coupled with a primitive-equation, free-surface oceanic component incorporating sea ice (coupled large-scale ice–ocean (CLIO)). By 2100, average Greenland annual temperature is found to rise by about 4.5˚C and mean precipitation by about 35%. the total fresh-water flux approximately doubles over this period due to increased runoff from the ice sheet and the ice-free land, but the calving rate is found to decrease by 25%. the ice sheet shrinks equivalent to 4 cm of sea-level rise. the contribution from the background evolution is not more than 5% of the total predicted sea-level rise. We did not find significant changes in the patterns of climate change over the North Atlantic region compared with a climate-change run without Greenland fresh-water feedback.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.3189/172756402781816537
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2002
    detail.hit.zdb_id: 2122400-6
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  • 2
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    Online Resource
    The Antarctic Ice Sheet During the Last Glacial-Interglacial Cycle: A Three-Dimensional Experiment
    International Glaciological Society ; 1990
    In:  Annals of Glaciology Vol. 14 ( 1990), p. 115-119
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 14 ( 1990), p. 115-119
    Abstract: A complete three-dimensional thermo-mechanical ice-shect model for the entire Antarctic ice sheet, including an ice shelf, grounding line-dynamics and isostatic bed adjustment, is employed to simulate the response of the ice sheet during the last glacial-interglacial cycle with respect to changing environmental conditions. To do this, the Vostok temperature signal is used to force changes in surface temperature and accumulation rate and sea level prescribed by a piecewise linear sawtooth function. Model calculations started at 160 ka B.P. In line with glacial geological evidence, the most pronounced fluctuations are found in the West Antarctic ice sheet and appear to be essentially controlled by changes in eustatic sea level. Grounding occurs more readily in the Weddell Sea than in the Ross Sea and, due to the long time scales involved, the ice sheet does not reach its full glacial extent until 16 ka B.p. The concomitant disintegration of the West Antarctic ice sheet is triggered by a rise in sea level and takes around 6000 years to complete. The ice sheet then halts close to the present state and no collapse takes place. This Holocene deglaciation appears to have added 6–8 million km 3 of ice to the world oceans, corresponding with an Antarctic contribution to world-wide sea level of 12–15 m.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.3189/S0260305500008387
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 1990
    detail.hit.zdb_id: 2122400-6
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  • 3
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    Online Resource
    A comparison of different ways of dealing with isostasy: examples from modelling the Antarctic ice sheet during the last glacial cycle
    International Glaciological Society ; 1996
    In:  Annals of Glaciology Vol. 23 ( 1996), p. 309-317
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 23 ( 1996), p. 309-317
    Abstract: The bedrock isostatic response exerts a strong control on ice-sheet dynamics and is therefore always taken into account in ice-sheet models. This paper reviews the various methods normally used in the ice-sheet modelling community to deal with the bedrock response and compares these with a more sophisticated full-Earth model. Each of these bedrock treatments, five in total, is coupled with a three-dimensional thermomechanical ice-sheet model under the same forcing conditions to simulate the Antarctic ice sheet during the last glacial cycle. The outputs of the simulations are compared on the basis of the time-dependent behaviour for the total ice volume and the mean bedrock elevation during the cycle and of the present rate of uplift over Antarctica. This comparison confirms the necessity of accounting for the elastic bending of the lithosphere in order to yield realistic bedrock patterns. It furthermore demonstrates the deficiencies inherent to the diffusion equation in modelling the complex deformation within the mantle. Nevertheless, when characteristic parameters are varied within their range of uncertainty, differences within one single method are often of the same order as those between the various methods. This overview finally attempts to point out the main advantages and drawbacks of each of these methods and to determine which one is most appropriate depending on the specific modelling requirements.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.3189/S0260305500013586
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 1996
    detail.hit.zdb_id: 2122400-6
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  • 4
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    Results from the Ice-Sheet Model Intercomparison Project–Heinrich Event Intercomparison (ISMIP HEINO)
    International Glaciological Society ; 2010
    In:  Journal of Glaciology Vol. 56, No. 197 ( 2010), p. 371-383
    Details
    In: Journal of Glaciology, International Glaciological Society, Vol. 56, No. 197 ( 2010), p. 371-383
    Abstract: Results from the Heinrich Event Intercomparison (HEINO) topic of the Ice-Sheet Model Intercomparison Project (ISMIP) are presented. ISMIP HEINO was designed to explore internal large-scale ice-sheet instabilities in different contemporary ice-sheet models. These instabilities are of interest because they are a possible cause of Heinrich events. A simplified geometry experiment reproduces the main characteristics of the Laurentide ice sheet, including the sedimented region over Hudson Bay and Hudson Strait. The model experiments include a standard run plus seven variations. Nine dynamic/thermodynamic ice-sheet models were investigated; one of these models contains a combination of the shallow-shelf (SSA) and shallow-ice approximation (SIA), while the remaining eight models are of SIA type only. Seven models, including the SIA–SSA model, exhibit oscillatory surges with a period of ∼1000 years for a broad range of parameters, while two models remain in a permanent state of streaming for most parameter settings. In a number of models, the oscillations disappear for high surface temperatures, strong snowfall and small sediment sliding parameters. In turn, low surface temperatures and low snowfall are favourable for the ice-surge cycles. We conclude that further improvement of ice-sheet models is crucial for adequate, robust simulations of cyclic large-scale instabilities.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.3189/002214310792447789
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2010
    detail.hit.zdb_id: 2140541-4
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  • 5
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    Online Resource
    Formation and disintegration of the Antarctic ice sheet
    International Glaciological Society ; 1994
    In:  Annals of Glaciology Vol. 20 ( 1994), p. 336-340
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 20 ( 1994), p. 336-340
    Abstract: A model of the Antarctic ice sheet has been used to simulate the ice sheet in warmer climates, in order to investigate what kind of ice-sheet geometries one can reasonably expect under what kind of climatic conditions and to discover which physical mechanisms may be involved to explain them. The results of these experiments reveal the considerable stability of; in particular, the East Antarctic ice sheet. It would require a temperature rise of between 17 and 20 K above present levels to remove this ice sheet from the subglacial basins in the interior of the continent and of 25 K to melt down the Antarctic ice sheet completely. For a temperature rise below 5 K, the model actually predicts a larger Antarctic ice sheet than today as a result of increased snowfall, whereas the west Antarctic ice sheet was round not to survive temperatures more than 8–10 K above present values. Furthermore, basal temperature conditions in these experiments point to the problems involved in raising the base of the ice sheet to the pressure-melting point over the large areas necessary to consider the possibility of sliding instability. These results bear on a lively debate regarding the late Cenozoic glacial history of Antarctica. Particularly, based on these findings, it is difficult to reconcile a highly variable East Antarctic ice sheet until the Pliocene with modest warming recorded in, for instance, the deep-sea records for the late Neogene.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.3189/172756494794587221
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 1994
    detail.hit.zdb_id: 2122400-6
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  • 6
    Online Resource
    Online Resource
    Formation and disintegration of the Antarctic ice sheet
    International Glaciological Society ; 1994
    In:  Annals of Glaciology Vol. 20 ( 1994), p. 336-340
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 20 ( 1994), p. 336-340
    Abstract: A model of the Antarctic ice sheet has been used to simulate the ice sheet in warmer climates, in order to investigate what kind of ice-sheet geometries one can reasonably expect under what kind of climatic conditions and to discover which physical mechanisms may be involved to explain them. The results of these experiments reveal the considerable stability of; in particular, the East Antarctic ice sheet. It would require a temperature rise of between 17 and 20 K above present levels to remove this ice sheet from the subglacial basins in the interior of the continent and of 25 K to melt down the Antarctic ice sheet completely. For a temperature rise below 5 K, the model actually predicts a larger Antarctic ice sheet than today as a result of increased snowfall, whereas the west Antarctic ice sheet was round not to survive temperatures more than 8–10 K above present values. Furthermore, basal temperature conditions in these experiments point to the problems involved in raising the base of the ice sheet to the pressure-melting point over the large areas necessary to consider the possibility of sliding instability. These results bear on a lively debate regarding the late Cenozoic glacial history of Antarctica. Particularly, based on these findings, it is difficult to reconcile a highly variable East Antarctic ice sheet until the Pliocene with modest warming recorded in, for instance, the deep-sea records for the late Neogene.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.1017/S0260305500016657
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 1994
    detail.hit.zdb_id: 2122400-6
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  • 7
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    Online Resource
    Surface mass balance of the Greenland ice sheet from climate-analysis data and accumulation/runoff models
    International Glaciological Society ; 2002
    In:  Annals of Glaciology Vol. 35 ( 2002), p. 67-72
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 35 ( 2002), p. 67-72
    Abstract: We used surface climate fields from high-resolution (~0.5660.56˚) European Centre for Medium-RangeWeather Forecasts (ECMWF) operational analyses (1992–98), together with meteorological and glaciological models of snow accumulation and surface meltwater runoff/retention, to produce novel maps of Greenland ice sheet (GIS) net accumulation, net runoff and surface mass balance (SMB). We compared our runoff maps with similar-scaled runoff (melt minus refreezing) maps based on passive-microwave satellite data. Our gross spatial/temporal patterns of runoff compared well with those from the satellite data, although amounts of modelled runoff are likely too low. Mean accumulation was 0.287 (0.307)ma –1 , and mean runoff was 0.128 (0.151)ma –1 , averaged across the W. Abdalati (T. L. Mote) GIS mask. Corresponding mean SMB was 0.159 (0.156)ma –1 , with considerable interannual variability (standard deviation ~0.11ma –1 ) primarily due to variations in runoff. Considering best estimates of current iceberg calving, overall the GIS is probably currently losing mass. Our study shows great promise for meaningfully modelling SMB based on forthcoming ``second-generation’’ ECMWF re-analysis (ERA-40) data, and comparing the results with ongoing laser/radarmeasurements of surface elevation. This should help elucidate to what extent surface elevation changes are caused by short-term SMB variations or other factors (e.g. ice dynamics).
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.3189/172756402781816744
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2002
    detail.hit.zdb_id: 2122400-6
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  • 8
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    Online Resource
    Thermomechanical modelling of Northern Hemisphere ice sheets with a two-level mass-balance parameterization
    International Glaciological Society ; 1995
    In:  Annals of Glaciology Vol. 21 ( 1995), p. 111-116
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 21 ( 1995), p. 111-116
    Abstract: A three-dimensional time-dependent thermomechanical ice-sheet model was used together with a two-level (snow-accumulation/runoff) mass-balance model to investigate the Quaternary ice sheets of the Northern Hemisphere. The model freely generates the ice-sheet geometry in response to specified changes in surface temperature and mass balance, and includes bedrock adjustment, basal sliding and a full temperature calculation within the ice. The mass-balance parameterization makes a distinction between snowfall and melting. Yearly snowfall rates depend on the present precipitation distribution, and are varied proportionally to changes in surface temperature and the moisture content of the air. The ablation model is based on the positive-degree-day method, and distinguishes between ice and snow melting. This paper discusses steady-slate characteristics, conditions for growth and retreat, and response time-scales of ice sheets as a function of a prescribed lowering of summer temperature. Most notably, the modelled extents of the Eurasian ice sheet for a summer temperature lowering of 6–7 K and of the Laurentide ice sheet for a cooling of 9–10 K are in reasonable agreement with most reconstructions based on geological evidence, except for the presence of a large ice sheet stretching from Alaska across the Bering Strait to most of eastern Siberia. In addition, wet basal conditions turned out to be always confined to the margin, whereas central areas in these reconstructions remained always cold-based. This is of relevance for processes involving reduced basal traction.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.1017/S0260305500015688
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 1995
    detail.hit.zdb_id: 2122400-6
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  • 9
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    Online Resource
    Steady-state characteristics of the Greenland ice sheet under different climates
    International Glaciological Society ; 1991
    In:  Journal of Glaciology Vol. 37, No. 125 ( 1991), p. 149-157
    Details
    In: Journal of Glaciology, International Glaciological Society, Vol. 37, No. 125 ( 1991), p. 149-157
    Abstract: The Greenland ice sheet is modelled to simulate its extent and volume in warmer climates, and to find out whether the ice sheet would re-form on the ice-free bedrock under present climatic conditions. The ice-sheet model is a three-dimensional thermo-mechanical model with a fine-resolution grid. The bedrock surface beneath the ice sheet was mapped using radio-echo-sounding measurements by the Electromagnetic Institute, Copenhagen. The model experiments show that increased temperature will result in ice-margin retreat, but the ice sheet is relatively stable; it takes a temperature rise of at least 6 deg for the ice sheet to disappear completely, which indicates that the ice sheet probably survived the last interglacial. Furthermore, it appears that the Greenland ice sheet is not a mere relict ice mass from a previously colder climate but that the ice sheet will still re-form on the bare bedrock under the present, or even slightly warmer, climatic conditions.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.3189/S0022143000042908
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 1991
    detail.hit.zdb_id: 2140541-4
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  • 10
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    Online Resource
    Basal temperature conditions of the Greenland ice sheet during the glacial cycles
    International Glaciological Society ; 1996
    In:  Annals of Glaciology Vol. 23 ( 1996), p. 226-236
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 23 ( 1996), p. 226-236
    Abstract: A high-resolution, three-dimensional thermomechanical ice-sheet model, which includes isostasy, the possibility of ice-sheet expansion on the continental shelf and refined climatic parameterizations, was used to investigate the basal thermal regime of the Greenland ice sheet. The thermodynamic calculations take into account the usual terms of heat flow within the ice, a thermally active bedrock layer and all of the effects associated with changes in ice thickness and flow pattern. Basal temperature conditions are documented with respect to glacial–interracial shifts in climatic boundary conditions, both in steady state as during simulations over the last two glacial cycles using the GRIP δ 18 0 record. It is found that the basal temperature field shows a large sensitivity in steady-state experiments but that, during a glacial cycle, basal temperature variations are strongly damped, in particular in central areas. A comparison has been made with measured data from deep ice cores and the implications are discussed.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.3189/S0260305500013483
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 1996
    detail.hit.zdb_id: 2122400-6
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