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  • 2015-2019  (6)
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  • 1
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    The sensitivity of Northern Hemisphere ice sheets to atmospheric forcing during the last glacial cycle using PMIP3 models (2019)
    Cambridge Univ. Press
    In:  Journal of Glaciology, 65 (252). pp. 645-661.
    Details
    Publication Date: 2021-01-08
    Description: 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: Article , PeerReviewed
    Format: text
    DOI: 10.1017/jog.2019.42
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Investigating the role of subglacial geology on ice sheet dynamics (2018)
    In:  EPIC3EGU General Assembly 2018, Vienna, Austria, 2018-04-07-2018-04-12
    Details
    Publication Date: 2019-01-04
    Description: Basal boundary conditions, such as basal geology, the presence of unconsolidated sediments, and hydrology, play a dominant role in the dynamics of ice sheets. One problem when studying existing ice sheets in Greenland and Antarctica is the lack of direct observations of these basal conditions. Studying paleo-ice sheet behaviour is advantageous in this respect, because these conditions are preserved in glacial landforms and sediments. By studying past ice sheet behaviour, we can provide analogues for modern behaviour. We investigate the role of basal geological conditions and hydrology on ice sheet dynamics using the ice sheet model PISM. We specifically focus on the North American ice sheet complex. We present datasets for this region that can be used in ice sheet models to investigate basal conditions including information on bedrock geology, the distribution of unconsolidated sediments, and the dominant grain size of the sediments. We use these datasets to investigate how they impact ice sheet dynamics with simulations over the last glacial cycle. We include a simple hydrology model that includes meltwater derived from the surface, and property changes depending on the basal geology from our datasets. Our results show that the behaviour of the ice sheet changes when there is a transition from regions with sparse sediment cover to complete sediment cover. One impact is that because ice can flow faster in regions like Hudson Bay, it can cause the Laurentide Ice Sheet to stabilize into a single continent-wide ice sheet faster than in a situation where sediments are not present. We also investigate the role of changes in basal geological conditions have in causing unstable behaviour in ice sheets.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
    Format: application/pdf
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    PAPER (OA)
  • 3
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    The sensitivity of Northern Hemisphere ice sheets to atmospheric forcing during the last glacial cycle using PMIP3 models (2019)
    INT GLACIOL SOC
    In:  EPIC3Journal of Glaciology, INT GLACIOL SOC, ISSN: 0022-1430
    Details
    Publication Date: 2019-07-22
    Description: 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.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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    PAPER (OA)
  • 4
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    Studying the impact of proglacial lakes on ice sheet dynamics (2018)
    In:  EPIC3European Geosciences Union General Assembly 2018, Vienna, 2018-04-09-2018-04-13
    Details
    Publication Date: 2018-04-23
    Description: Proglacial lakes have an important impact on the dynamics of ice sheets by imposing a marine-like boundary condition to the ice margin. At the ice-ocean interface the ice sheet is know to have a complex dynamical behavior. These processes can include the formation of ice shelves that can buttress glaciers, increase subglacial melting, reduce basal friction and calving of icebergs. Such processes also act at the boundaries at ice-marginal lakes, which arose along the ice margins of past continental ice sheets. Some of these lakes spanned several hundreds of kilometers. We have implemented a module into the Parallel Ice Sheet Model (PISM) to study the impacts of proglacial lakes on the ice dynamics. This model dynamically updates the lake basins by filling all depressions of the domain until they overflow. This simple approach does not calculate a water budget and therefore does not rely on an advanced and computationally expensive hydrology model. The lake boundaries are treated in a similar way as a marine boundary. We test this model by reconstructing the evolution of the North American ice sheets by using a transient climate forcing for the last glacial cycle. These reconstructions are then compared to geological records, such as ice margins and paleo-lake shorelines.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
    Format: application/pdf
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    PAPER (OA)
  • 5
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    Hydrodynamical experiments with Lattice Boltzmann models (2015)
    In:  EPIC3
    Details
    Publication Date: 2015-03-03
    Description: In this thesis different numerical models based on the lattice Boltzmann equation presented and tested. Therefore the models are applied to two classical two-dimensional hydrodynamical problems. Parameter studies are performed with particular regard to changes in flow dynamics at hydrodynamical instabilities. The iLBGK model [Z. Guo et al., 2000] with a D2Q9 lattice is used to study the 2D flow past a cylinder placed between two walls. The transition from a steady flow to a vortex shedding regime is analyzed by varying the Reynolds number and the distance of the cylinder to one wall. Due to interaction of the cylinder's wake with the wall vorticity, the transition is delayed as the cylinder approaches the wall. The results are compared with the findings of Zovatto & Pedrizzetti [2001]. For the simulation of thermal flows, the multi-distribution-function (MDF) approach [Z. Guo et al., 2002a; He et al., 1998] is used. This approach uses the Boussinesq approximation to separate the liquid and the thermal components of the flow, which are solved on separate lattices. Two implementations of this approach are carried out using the LBGK and MRT models [Ginzburg, 2005; Wang et al., 2013]. These thermal models are used to study the 2D Rayleigh-Bénard problem for a fixed Prandtl number Pr = 0.71. The transition from the solely conductive to the convective regime is found to be dependent on the wavenumber k of a perturbation. The usage of lateral periodic boundary conditions restricts the possible values for k, which depend on the aspect ratio of the numerical domain. Checked against theoretical results, the critical Rayleigh numbers obtained with the MRT model are found to be more accurate than those obtained with the LBGK model.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Thesis , notRev
    Format: application/pdf
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  • 6
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    LakeCC: a tool for efficiently identifying lake basins with application to palaeogeographic reconstructions of North America (2019)
    JOHN WILEY & SONS LTD
    In:  EPIC3Journal of Quaternary Science, JOHN WILEY & SONS LTD, ISSN: 0267-8179
    Details
    Publication Date: 2021-02-16
    Description: Along the margins of continental ice sheets, lakes formed in isostatically depressed basins during glacial retreat. Their shorelines and extent are sensitive to the ice margin and the glacial history of the region. Proglacial lakes, in turn, also impact the glacial isostatic adjustment due to loading, and ice dynamics by posing a marine‐like boundary condition at the ice margin. In this study we present a tool that efficiently identifies lake basins and the corresponding maximum water level for a given ice sheet and topography reconstruction. This algorithm, called the LakeCC model, iteratively checks the whole map for a set of increasing water levels and fills isolated basins until they overflow into the ocean. We apply it to the present‐day Great Lakes and the results show good agreement (∼1−4%) with measured lake volume and depth. We then apply it to two topography reconstructions of North America between the Last Glacial Maximum and the present. The model successfully reconstructs glacial lakes such as Lake Agassiz, Lake McConnell and the predecessors of the Great Lakes. LakeCC can be used to judge the quality of ice sheet reconstructions.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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