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  • Copernicus  (46)
  • AGU (American Geophysical Union)  (2)
  • Macmillian Magazines Ltd.  (2)
  • Air and Waste Managment Association Publication
  • 1
    Electronic Resource
    Electronic Resource
    Rapid changes of glacial climate simulated in a coupled climate model (2001)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 409 (2001), S. 153-158 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Abrupt changes in climate, termed Dansgaard–Oeschger and Heinrich events, have punctuated the last glacial period (∼100–10 kyr ago) but not the Holocene (the past 10 kyr). Here we use an intermediate-complexity climate model to investigate the stability of glacial ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35051500
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  • 2
    Electronic Resource
    Electronic Resource
    North Pacific seasonality and the glaciation of North America 2.7 million years ago (2005)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 433 (2005), S. 821-825 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] In the context of gradual Cenozoic cooling, the timing of the onset of significant Northern Hemisphere glaciation 2.7 million years ago is consistent with Milankovitch's orbital theory, which posited that ice sheets grow when polar summertime insolation and temperature are low. However, the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature03332
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  • 3
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    Simulation of climate, ice sheets and CO2 evolution during the last four glacial cycles with an Earth system model of intermediate complexity (2017)
    Copernicus
    Details
    Publication Date: 2017-11-29
    Description: In spite of significant progress in paleoclimate reconstructions and modelling of different aspects of the past glacial cycles, the mechanisms which transform regional and seasonal variations in solar insolation into long-term and global-scale glacial–interglacial cycles are still not fully understood – in particular, in relation to CO2 variability. Here using the Earth system model of intermediate complexity CLIMBER-2 we performed simulations of the co-evolution of climate, ice sheets, and carbon cycle over the last 400 000 years using the orbital forcing as the only external forcing. The model simulates temporal dynamics of CO2, global ice volume, and other climate system characteristics in good agreement with paleoclimate reconstructions. These results provide strong support for the idea that long and strongly asymmetric glacial cycles of the late Quaternary represent a direct but strongly nonlinear response of the Northern Hemisphere ice sheets to orbital forcing. This response is strongly amplified and globalised by the carbon cycle feedbacks. Using simulations performed with the model in different configurations, we also analyse the role of individual processes and sensitivity to the choice of model parameters. While many features of simulated glacial cycles are rather robust, some details of CO2 evolution, especially during glacial terminations, are sensitive to the choice of model parameters. Specifically, we found two major regimes of CO2 changes during terminations: in the first one, when the recovery of the Atlantic meridional overturning circulation (AMOC) occurs only at the end of the termination, a pronounced overshoot in CO2 concentration occurs at the beginning of the interglacial and CO2 remains almost constant during the interglacial or even declines towards the end, resembling Eemian CO2 dynamics. However, if the recovery of the AMOC occurs in the middle of the glacial termination, CO2 concentration continues to rise during the interglacial, similar to the Holocene. We also discuss the potential contribution of the brine rejection mechanism for the CO2 and carbon isotopes in the atmosphere and the ocean during the past glacial termination.
    Print ISSN: 1814-9324
    Electronic ISSN: 1814-9332
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 4
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    Comparison of surface mass balance of ice sheets simulated by positive-degree-day method and energy balance approach (2017)
    Copernicus
    Details
    Publication Date: 2017-07-07
    Description: Glacial cycles of the late Quaternary are controlled by the asymmetrically varying mass balance of continental ice sheets in the Northern Hemisphere. Surface mass balance is governed by processes of ablation and accumulation. Here two ablation schemes, the positive-degree-day (PDD) method and the surface energy balance (SEB) approach, are compared in transient simulations of the last glacial cycle with the Earth system model of intermediate complexity CLIMBER-2. The standard version of the CLIMBER-2 model incorporates the SEB approach and simulates ice volume variations in reasonable agreement with paleoclimate reconstructions during the entire last glacial cycle. Using results from the standard CLIMBER-2 model version, we simulated ablation with the PDD method in offline mode by applying different combinations of three empirical parameters of the PDD scheme. We found that none of the parameter combinations allow us to simulate a surface mass balance of the American and European ice sheets that is similar to that obtained with the standard SEB method. The use of constant values for the empirical PDD parameters led either to too much ablation during the first phase of the last glacial cycle or too little ablation during the final phase. We then substituted the standard SEB scheme in CLIMBER-2 with the PDD scheme and performed a suite of fully interactive (online) simulations of the last glacial cycle with different combinations of PDD parameters. The results of these simulations confirmed the results of the offline simulations: no combination of PDD parameters realistically simulates the evolution of the ice sheets during the entire glacial cycle. The use of constant parameter values in the online simulations leads either to a buildup of too much ice volume at the end of glacial cycle or too little ice volume at the beginning. Even when the model correctly simulates global ice volume at the last glacial maximum (21 ka), it is unable to simulate complete deglaciation during the Holocene. According to our simulations, the SEB approach proves superior for simulations of glacial cycles.
    Print ISSN: 1814-9324
    Electronic ISSN: 1814-9332
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 5
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    Submarine melt parameterization for a Greenland glacial system model (2017)
    Copernicus
    Details
    Publication Date: 2017-01-04
    Description: Two hundreds of marine-terminating Greenland outlet glaciers deliver more than half of the annually accumulated ice into the ocean and play an important role in the Greenland ice sheet mass loss observed since the mid 1990s. Submarine melt plays a crucial role in the mass balance and position of the grounding line of these outlet glaciers. As the ocean warms, it is expected that submarine melt will increase and outlet glaciers will retreat, contributing to sea level rise. Projections of the future contribution of outlet glaciers to sea level rise is hampered by the necessity to use extremely high resolution of the order of a few hundred meters both for modelling of the outlet glaciers and as well as coupling them with high resolution 3D ocean models. In addition fjord bathymetry data are mostly missing or are inaccurate (errors of several 100s of meters), which questions the benefit of using computational expensive 3D models for future predictions. Here we propose an alternative approach based on using of computationally efficient parameterization of submarine melt based on turbulent plume theory. We show that such parameterization is in a reasonable agreement with several available modeling studies. We performed a suit of experiments to analyse sensitivity of these parameterizations to model parameters and climate characteristics. We found that the computationally cheap plume model demonstrates qualitatively similar behaviour as 3D gerneral circulation models. To match results of the 3D models in a quantitative manner, a scaling factor in the order of one is needed for the plume models. We applied this approach to model submarine melt for six representative Greenland glaciers and found that the parameterization of a line plume can produce submarine melt compatible with observational data. Our results show that the line plume model is more appropriate than the cone plume model for simulating the submarine melting of real glaciers in Greenland.
    Print ISSN: 1994-0432
    Electronic ISSN: 1994-0440
    Topics: Geography , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 6
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    The importance of snow albedo for ice sheet evolution over the last glacial cycle (2017)
    Copernicus
    Details
    Publication Date: 2017-10-17
    Description: The surface energy and mass balance of ice sheets strongly depends on the amount of solar radiation absorbed at the surface, which is mainly controlled by the albedo of snow and ice. Here, using an Earth system model of intermediate complexity, we explore the role played by surface albedo for the simulation of glacial cycles. We show that the evolution of the Northern Hemisphere ice sheets over the last glacial cycle is very sensitive to the representation of snow albedo in the model. It is well known that the albedo of snow depends strongly on the snow grain size and the content of light absorbing impurities. Excluding either the snow aging effect or the dust darkening effect on snow albedo leads to an excessive ice build-up during glacial times and consequently to a failure in simulating deglaciation. While the effect of snow grain growth on snow albedo is well constrained, the albedo reduction due to the presence of dust in snow is much more uncertain, because the light absorbing properties of dust vary widely as a function of dust mineral composition. We also show that assuming slightly different optical properties of dust leads to very different ice sheet and climate evolutions in the model. Conversely, ice sheet evolution is less sensitive to the choice of ice albedo in the model. We conclude that a proper representation of snow albedo is a fundamental prerequisite for a successful simulation of glacial cycles.
    Print ISSN: 1814-9340
    Electronic ISSN: 1814-9359
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 7
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    Simulation of climate, ice sheets and CO2 evolution during the last four glacial cycles with an Earth system model of intermediate complexity (2017)
    Copernicus
    Details
    Publication Date: 2017-04-19
    Description: In spite of significant progress in paleoclimate reconstructions and modeling of different aspects of the past glacial cycles, the mechanisms which transform regional and seasonal variations in solar insolation into long-term and global-scale glacial-interglacial cycles are still not fully understood, in particular, for CO2 variability. Here using the Earth system model of intermediate complexity CLIMBER-2 we performed simulations of co-evolution of climate, ice sheets and carbon cycle over the last 400,000 years using the orbital forcing as the only external forcing. The model simulates temporal dynamics of CO2, global ice volume and other climate system characteristics in good agreement with paleoclimate reconstructions. Using simulations performed with the model in different configurations, we also analyze the role of individual processes and sensitivity to the choice of model parameters. While many features of simulated glacial cycles are rather robust, some details of CO2 evolution, especially during glacial terminations, are rather sensitive to the choice of model parameters. Specifically, we found two major regimes of CO2 changes during terminations: in the first one, when the recovery of the Atlantic meridional overturning circulation (AMOC) occurs only at the end of the termination, a pronounced overshoot in CO2 concentration occurs at the beginning of the interglacial and CO2 remains almost constant during interglacial or even decline towards the end, resembling Eemian CO2 dynamics. However, if the recovery of the AMOC occurs in the middle of the glacial termination, CO2 concentration continues to rise during interglacial, similar to Holocene. We also discuss potential contribution of the brine rejection mechanism for the CO2 and carbon isotopes in the atmosphere and the ocean during the past glacial termination.
    Print ISSN: 1814-9340
    Electronic ISSN: 1814-9359
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 8
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    Corrigendum to "An efficient regional energy-moisture balance model for simulation of the Greenland Ice Sheet response to climate change" published in The Cryosphere, 4, 129–144, 2010 (2010)
    Copernicus
    Details
    Publication Date: 2010-04-21
    Print ISSN: 1994-0416
    Electronic ISSN: 1994-0424
    Topics: Geography , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 9
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    An efficient regional energy-moisture balance model for simulation of the Greenland ice sheet response to climate change (2009)
    Copernicus
    Details
    Publication Date: 2009-09-11
    Description: In order to explore the response of the Greenland ice sheet (GIS) to climate change on long (centennial to multi-millennial) time scales, a regional energy-moisture balance model has been developed. This model simulates seasonal variations of temperature and precipitation over Greenland and explicitly accounts for elevation and albedo feedbacks. These fields are used to force a high resolution ice sheet model through the annual mean surface temperature and mass balance. The melt component of the mass balance is computed here using both a conventional positive degree day approach and a more physically-based alternative. As a validation of the model, we first simulated temperature and precipitation over Greenland for the prescribed, present-day topography of Greenland and compared them with empirical data. For the present-day climate, simulated surface boundary conditions for the GIS do not differ significantly from those of a simple parameterization used in many previous simulations. However, for a prescribed, ice-free state, the differences in simulated climatology and surface mass balance between the regional energy-moisture balance model and the conventional approach become significant, with our model showing much stronger summer warming. When coupled to a high resolution, three-dimensional ice sheet model and initialized with present-day conditions, the two melt schemes both allow sufficiently realistic simulations of the present-day GIS. However, when starting from ice-free conditions, two different equilibrium states are achieved, depending on the choice of melt scheme.
    Print ISSN: 1994-0432
    Electronic ISSN: 1994-0440
    Topics: Geography , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 10
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    Simulating the Greenland ice sheet under present-day and palaeo constraints including a new discharge parameterization (2014)
    Copernicus
    Details
    Publication Date: 2014-02-17
    Description: In this paper, we propose a new sub-grid scale parameterization for the ice discharge into the ocean through outlet glaciers and inspect the role of different observational and palaeo constraints for the choice of an optimal set of model parameters. This parameterization was introduced into the polythermal ice-sheet model SICOPOLIS, which is coupled to the regional climate model of intermediate complexity REMBO. Using the coupled model, we performed large ensemble simulations over the last two glacial cycles. We exploit two major parameters: a melt parameter in the surface melt scheme of REMBO and an ice discharge parameter in our parameterization of ice discharge. Our constraints are the present-day Greenland ice sheet surface elevation, surface mass balance partition (ratio between ice discharge and total precipitation) and the Eemian interglacial elevation drop relative to present-day in the vicinity of the NEEM ice core. We show that the ice discharge parameterization enables us to simulate both the correct ice-sheet shape and mass balance partition at the same time without explicitly resolving the Greenland outlet glaciers. For model verification, we compare simulated total and sectoral ice discharge with those from other findings, including observations. For the model versions, which are inside the range of observational and palaeo constraints, our simulated Greenland ice sheet contribution to Eemian sea level rise relative to present-day amounts to 1.4 m on average (in the range of 0.6 and 2.5 m).
    Print ISSN: 1994-0432
    Electronic ISSN: 1994-0440
    Topics: Geography , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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