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  • Cambridge University Press (CUP)  (4)
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  • Cambridge University Press (CUP)  (4)
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  • 1
    Online Resource
    Online Resource
    The impact of spatially varying ice sheet basal conditions on sliding at glacial time scales
    Cambridge University Press (CUP) ; 2023
    In:  Journal of Glaciology Vol. 69, No. 276 ( 2023-08), p. 1056-1070
    Details
    In: Journal of Glaciology, Cambridge University Press (CUP), Vol. 69, No. 276 ( 2023-08), p. 1056-1070
    Abstract: Spatially variable basal conditions are thought to govern how ice sheets behave at glacial time scales ( 〉 1000 years) and responsible for changes in dynamics between the core and peripheral regions of the Laurentide and Fennoscandian ice sheets. Basal motion is accomplished via the deformation of unconsolidated sediments, or via sliding of the ice over an undeformable bed. We present an ice sheet sliding module for the Parallel Ice Sheet Model (PISM) that takes into account changes in sediment cover and incorporates surface meltwater. This model routes meltwater, produced at the surface and base of the ice sheet, toward the margin of the ice sheet. Basal sliding is accomplished through the deformation of water saturated sediments, or sliding at the ice-bed interface. In areas with continuous, water saturated sediments, sliding is almost always accomplished through sediment deformation. In areas with incomplete cover, sliding has a stronger dependence on the supply of water. We find that the addition of surface meltwater to the base is a more important factor for ice sheet evolution than the style of sliding. In a glacial cycle simulation, our model causes a more rapid buildup of the Laurentide Ice Sheet.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.1017/jog.2022.125
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2023
    detail.hit.zdb_id: 2140541-4
    SSG: 14
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  • 2
    Online Resource
    Online Resource
    A Short Note on Marine Reservoir Age Simulations Used in IntCal20
    Cambridge University Press (CUP) ; 2020
    In:  Radiocarbon Vol. 62, No. 4 ( 2020-08), p. 865-871
    Details
    In: Radiocarbon, Cambridge University Press (CUP), Vol. 62, No. 4 ( 2020-08), p. 865-871
    Abstract: Beyond ~13.9 cal kBP, the IntCal20 radiocarbon ( 14 C) calibration curve is based upon combining data across a range of different archives including corals and planktic foraminifera. In order to reliably incorporate such marine data into an atmospheric curve, we need to resolve these records into their constituent atmospheric signal and marine reservoir age. We present results of marine reservoir age simulations enabling this resolution, applying the LSG ocean general circulation model forced with various climatic background conditions and with atmospheric radiocarbon changes according to the Hulu Cave speleothem record. Simulating the spatiotemporal evolution of reservoir ages between 54,000 and 10,700 cal BP, we find reservoir ages between 500 and 1400 yr in the low- and mid-latitudes, but also more than 3000 yr in the polar seas. Our results are broadly in agreement with available marine radiocarbon reconstructions, with the caveat that continental margins, marginal seas, or tropical lagoons are not properly resolved in our coarse-resolution model.
    Type of Medium: Online Resource
    ISSN: 0033-8222 , 1945-5755
    URL: Article
    DOI: 10.1017/RDC.2020.9
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2020
    detail.hit.zdb_id: 2028560-7
    SSG: 11
    SSG: 13
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  • 3
    Online Resource
    Online Resource
    Estimating Greenland surface melt is hampered by melt induced dampening of temperature variability
    Cambridge University Press (CUP) ; 2018
    In:  Journal of Glaciology Vol. 64, No. 244 ( 2018-04), p. 227-235
    Details
    In: Journal of Glaciology, Cambridge University Press (CUP), Vol. 64, No. 244 ( 2018-04), p. 227-235
    Abstract: The positive degree-day (PDD) model provides a particularly simple approach to estimate surface melt from land ice based solely on air temperature. Here, we use a climate and snow pack simulation of the Greenland ice sheet (Modèle Atmosphérique Régional, MAR) as a reference, to analyze this scheme in three realizations that incorporate the sub-monthly temperature variability differently: (i) by local values, (ii) by local values that systematically overestimate the dampened variability associated with intense melting or (iii) by one constant value. Local calibrations reveal that incorporating local temperature variability, particularly resolving the dampened variability of melt areas, renders model parameters more temperature-dependent. This indicates that the negative feedback between surface melt and temperature variability introduces a non-linearity into the temperature – melt relation. To assess the skill of the individual realizations, we hindcast melt rates from MAR temperatures for each realization. For this purpose, we globally calibrate Greenland-wide, constant parameters. Realization (i) exhibits shortcomings in the spatial representation of surface melt unless temperature-dependent instead of constant parameters are calibrated. The other realizations perform comparatively well with constant parametrizations. The skill of the PDD model primarily depends, however, on the consistent calibration rather than on the specific representation of variability.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.1017/jog.2018.10
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2018
    detail.hit.zdb_id: 2140541-4
    SSG: 14
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  • 4
    Online Resource
    Online Resource
    The sensitivity of Northern Hemisphere ice sheets to atmospheric forcing during the last glacial cycle using PMIP3 models
    Cambridge University Press (CUP) ; 2019
    In:  Journal of Glaciology Vol. 65, No. 252 ( 2019-08), p. 645-661
    Details
    In: Journal of Glaciology, Cambridge University Press (CUP), Vol. 65, No. 252 ( 2019-08), p. 645-661
    Abstract: The evolution of Northern Hemisphere ice sheets through the last glacial cycle is simulated with the glacial index method by using the climate forcing from one General Circulation Model, COSMOS. By comparing the simulated results to geological reconstructions, we first show that the modelled climate is capable of capturing the main features of the ice-sheet evolution. However, large deviations exist, likely due to the absence of nonlinear interactions between ice sheet and other climate components. The model uncertainties of the climate forcing are examined using the output from nine climate models from the Paleoclimate Modelling Intercomparison Project Phase III. The results show a large variability in simulated ice sheets between the different models. We find that the ice-sheet extent pattern resembles summer surface air temperature pattern at the Last Glacial Maximum, confirming the dominant role of surface ablation process for high-latitude Northern Hemisphere ice sheets. This study shows the importance of the upper boundary condition for ice-sheet modelling, and implies that careful constraints on climate output is essential for simulating realistic glacial Northern Hemisphere ice sheets.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.1017/jog.2019.42
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2019
    detail.hit.zdb_id: 2140541-4
    SSG: 14
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