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17 results on '"B. de Fleurian"'

1. Impact of runoff temporal distribution on ice dynamics

Author

B. de Fleurian, R. Davy, and P. M. Langebroek

Subjects
Environmental sciences, GE1-350, Geology, QE1-996.5
Abstract

Record highs of meltwater production at the surface of the Greenland ice sheet have been recorded with a high recurrence over the last decades. Those melt seasons with longer durations, larger intensities, or with both increased length and melt intensity have a direct impact on the surface mass balance of the ice sheet and on its contribution to sea level rise. Moreover, the surface melt also affects the ice dynamics through the meltwater lubrication feedback. It is still not clear how the meltwater lubrication feedback impacts the long-term ice velocities on the Greenland ice sheet. Here we take a modeling approach with simplified ice sheet geometry and climate forcings to investigate in more detail the impacts of the changing characteristics of the melt season on ice dynamics. We model the ice dynamics through the coupling of the Double Continuum (DoCo) subglacial hydrology model with a shallow shelf approximation for the ice dynamics in the Ice-sheet and Sea-level System Model (ISSM). The climate forcing is generated from the ERA5 dataset to allow the length and intensity of the melt season to be varied in a comparable range of values. Our simulations present different behaviors between the lower and higher part of the glacier, but overall, a longer melt season will yield a faster glacier for a given runoff value. However, an increase in the intensity of the melt season, even under increasing runoff, tends to reduce glacier velocities. Those results emphasize the complexity of the meltwater lubrication feedback and urge us to use subglacial drainage models with both inefficient and efficient drainage components to give an accurate assessment of its impact on the overall dynamics of the Greenland ice sheet.

Published
2022
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2. Geometric controls of tidewater glacier dynamics

Author

T. Frank, H. Åkesson, B. de Fleurian, M. Morlighem, and K. H. Nisancioglu

Subjects
Environmental sciences, GE1-350, Geology, QE1-996.5
Abstract

Retreat of marine outlet glaciers often initiates depletion of inland ice through dynamic adjustments of the upstream glacier. The local topography of a fjord may promote or inhibit such retreat, and therefore fjord geometry constitutes a critical control on ice sheet mass balance. To quantify the processes of ice–topography interactions and enhance the understanding of the dynamics involved, we analyze a multitude of topographic fjord settings and scenarios using the Ice-sheet and Sea-level System Model (ISSM). We systematically study glacier retreat through a variety of artificial fjord geometries and quantify the modeled dynamics directly in relation to topographic features. We find that retreat in an upstream-widening or upstream-deepening fjord does not necessarily promote retreat, as suggested by previous studies. Conversely, it may stabilize a glacier because converging ice flow towards a constriction enhances lateral and basal shear stress gradients. An upstream-narrowing or upstream-shoaling fjord, in turn, may promote retreat since fjord walls or bed provide little stability to the glacier where ice flow diverges. Furthermore, we identify distinct quantitative relationships directly linking grounding line discharge and retreat rate to fjord topography and transfer these results to a long-term study of the retreat of Jakobshavn Isbræ. These findings offer new perspectives on ice–topography interactions and give guidance to an ad hoc assessment of future topographically induced ice loss based on knowledge of the upstream fjord geometry.

Published
2022
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3. Exceptionally high heat flux needed to sustain the Northeast Greenland Ice Stream

Author

S. Smith-Johnsen, B. de Fleurian, N. Schlegel, H. Seroussi, and K. Nisancioglu

Subjects
Environmental sciences, GE1-350, Geology, QE1-996.5
Abstract

The Northeast Greenland Ice Stream (NEGIS) currently drains more than 10 % of the Greenland Ice Sheet area and has recently undergone significant dynamic changes. It is therefore critical to accurately represent this feature when assessing the future contribution of Greenland to sea level rise. At present, NEGIS is reproduced in ice sheet models by inferring basal conditions using observed surface velocities. This approach helps estimate conditions at the base of the ice sheet but cannot be used to estimate the evolution of basal drag in time, so it is not a good representation of the evolution of the ice sheet in future climate warming scenarios. NEGIS is suggested to be initiated by a geothermal heat flux anomaly close to the ice divide, left behind by the movement of Greenland over the Icelandic plume. However, the heat flux underneath the ice sheet is largely unknown, except for a few direct measurements from deep ice core drill sites. Using the Ice Sheet System Model (ISSM), with ice dynamics coupled to a subglacial hydrology model, we investigate the possibility of initiating NEGIS by inserting heat flux anomalies with various locations and intensities. In our model experiment, a minimum heat flux value of 970 mW m−2 located close to the East Greenland Ice-core Project (EGRIP) is required locally to reproduce the observed NEGIS velocities, giving basal melt rates consistent with previous estimates. The value cannot be attributed to geothermal heat flux alone and we suggest hydrothermal circulation as a potential explanation for the high local heat flux. By including high heat flux and the effect of water on sliding, we successfully reproduce the main characteristics of NEGIS in an ice sheet model without using data assimilation.

Published
2020
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4. Simulated retreat of Jakobshavn Isbræ since the Little Ice Age controlled by geometry

Author

N. Steiger, K. H. Nisancioglu, H. Åkesson, B. de Fleurian, and F. M. Nick

Subjects
Environmental sciences, GE1-350, Geology, QE1-996.5
Abstract

Rapid retreat of Greenland's marine-terminating glaciers coincides with regional warming trends, which have broadly been used to explain these rapid changes. However, outlet glaciers within similar climate regimes experience widely contrasting retreat patterns, suggesting that the local fjord geometry could be an important additional factor. To assess the relative role of climate and fjord geometry, we use the retreat history of Jakobshavn Isbræ, West Greenland, since the Little Ice Age (LIA) maximum in 1850 as a baseline for the parameterization of a depth- and width-integrated ice flow model. The impact of fjord geometry is isolated by using a linearly increasing climate forcing since the LIA and testing a range of simplified geometries.We find that the total length of retreat is determined by external factors – such as hydrofracturing, submarine melt and buttressing by sea ice – whereas the retreat pattern is governed by the fjord geometry. Narrow and shallow areas provide pinning points and cause delayed but rapid retreat without additional climate warming, after decades of grounding line stability. We suggest that these geometric pinning points may be used to locate potential sites for moraine formation and to predict the long-term response of the glacier. As a consequence, to assess the impact of climate on the retreat history of a glacier, each system has to be analyzed with knowledge of its historic retreat and the local fjord geometry.

Published
2018
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5. Two independent methods for mapping the grounding line of an outlet glacier – an example from the Astrolabe Glacier, Terre Adélie, Antarctica

Author

E. Le Meur, M. Sacchettini, S. Garambois, E. Berthier, A. S. Drouet, G. Durand, D. Young, J. S. Greenbaum, J. W. Holt, D. D. Blankenship, E. Rignot, J. Mouginot, Y. Gim, D. Kirchner, B. de Fleurian, O. Gagliardini, and F. Gillet-Chaulet

Subjects
Environmental sciences, GE1-350, Geology, QE1-996.5
Abstract

The grounding line is a key element of coastal outlet glaciers, acting on their dynamics. Accurately knowing its position is fundamental for both modelling the glacier dynamics and establishing a benchmark for later change detection. Here we map the grounding line of the Astrolabe Glacier in East Antarctica (66°41' S, 140°05' E), using both hydrostatic and tidal methods. The first method is based on new surface and ice thickness data from which the line of buoyant floatation is found. The second method uses kinematic GPS measurements of the tidal response of the ice surface. By detecting the transitions where the ice starts to move vertically in response to the tidal forcing we determine control points for the grounding line position along GPS profiles. Employing a two-dimensional elastic plate model, we compute the rigid short-term behaviour of the ice plate and estimate the correction required to compare the kinematic GPS control points with the previously determined line of floatation. These two approaches show consistency and lead us to propose a grounding line for the Astrolabe Glacier that significantly deviates from the lines obtained so far from satellite imagery.

Published
2014
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6. A double continuum hydrological model for glacier applications

Author

B. de Fleurian, O. Gagliardini, T. Zwinger, G. Durand, E. Le Meur, D. Mair, and P. Råback

Subjects
Environmental sciences, GE1-350, Geology, QE1-996.5
Abstract

The flow of glaciers and ice streams is strongly influenced by the presence of water at the interface between ice and bed. In this paper, a hydrological model evaluating the subglacial water pressure is developed with the final aim of estimating the sliding velocities of glaciers. The global model fully couples the subglacial hydrology and the ice dynamics through a water-dependent friction law. The hydrological part of the model follows a double continuum approach which relies on the use of porous layers to compute water heads in inefficient and efficient drainage systems. This method has the advantage of a relatively low computational cost that would allow its application to large ice bodies such as Greenland or Antarctica ice streams. The hydrological model has been implemented in the finite element code Elmer/Ice, which simultaneously computes the ice flow. Herein, we present an application to the Haut Glacier d'Arolla for which we have a large number of observations, making it well suited to the purpose of validating both the hydrology and ice flow model components. The selection of hydrological, under-determined parameters from a wide range of values is guided by comparison of the model results with available glacier observations. Once this selection has been performed, the coupling between subglacial hydrology and ice dynamics is undertaken throughout a melt season. Results indicate that this new modelling approach for subglacial hydrology is able to reproduce the broad temporal and spatial patterns of the observed subglacial hydrological system. Furthermore, the coupling with the ice dynamics shows good agreement with the observed spring speed-up.

Published
2014
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7. Capabilities and performance of Elmer/Ice, a new-generation ice sheet model

Author

O. Gagliardini, T. Zwinger, F. Gillet-Chaulet, G. Durand, L. Favier, B. de Fleurian, R. Greve, M. Malinen, C. Martín, P. Råback, J. Ruokolainen, M. Sacchettini, M. Schäfer, H. Seddik, and J. Thies

Subjects
Geology, QE1-996.5
Abstract

The Fourth IPCC Assessment Report concluded that ice sheet flow models, in their current state, were unable to provide accurate forecast for the increase of polar ice sheet discharge and the associated contribution to sea level rise. Since then, the glaciological community has undertaken a huge effort to develop and improve a new generation of ice flow models, and as a result a significant number of new ice sheet models have emerged. Among them is the parallel finite-element model Elmer/Ice, based on the open-source multi-physics code Elmer. It was one of the first full-Stokes models used to make projections for the evolution of the whole Greenland ice sheet for the coming two centuries. Originally developed to solve local ice flow problems of high mechanical and physical complexity, Elmer/Ice has today reached the maturity to solve larger-scale problems, earning the status of an ice sheet model. Here, we summarise almost 10 yr of development performed by different groups. Elmer/Ice solves the full-Stokes equations, for isotropic but also anisotropic ice rheology, resolves the grounding line dynamics as a contact problem, and contains various basal friction laws. Derived fields, like the age of the ice, the strain rate or stress, can also be computed. Elmer/Ice includes two recently proposed inverse methods to infer badly known parameters. Elmer is a highly parallelised code thanks to recent developments and the implementation of a block preconditioned solver for the Stokes system. In this paper, all these components are presented in detail, as well as the numerical performance of the Stokes solver and developments planned for the future.

Published
2013
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8. Results of the Marine Ice Sheet Model Intercomparison Project, MISMIP

Author

F. Pattyn, C. Schoof, L. Perichon, R. C. A. Hindmarsh, E. Bueler, B. de Fleurian, G. Durand, O. Gagliardini, R. Gladstone, D. Goldberg, G. H. Gudmundsson, P. Huybrechts, V. Lee, F. M. Nick, A. J. Payne, D. Pollard, O. Rybak, F. Saito, and A. Vieli

Subjects
Environmental sciences, GE1-350, Geology, QE1-996.5
Abstract

Predictions of marine ice-sheet behaviour require models that are able to robustly simulate grounding line migration. We present results of an intercomparison exercise for marine ice-sheet models. Verification is effected by comparison with approximate analytical solutions for flux across the grounding line using simplified geometrical configurations (no lateral variations, no effects of lateral buttressing). Unique steady state grounding line positions exist for ice sheets on a downward sloping bed, while hysteresis occurs across an overdeepened bed, and stable steady state grounding line positions only occur on the downward-sloping sections. Models based on the shallow ice approximation, which does not resolve extensional stresses, do not reproduce the approximate analytical results unless appropriate parameterizations for ice flux are imposed at the grounding line. For extensional-stress resolving "shelfy stream" models, differences between model results were mainly due to the choice of spatial discretization. Moving grid methods were found to be the most accurate at capturing grounding line evolution, since they track the grounding line explicitly. Adaptive mesh refinement can further improve accuracy, including fixed grid models that generally perform poorly at coarse resolution. Fixed grid models, with nested grid representations of the grounding line, are able to generate accurate steady state positions, but can be inaccurate over transients. Only one full-Stokes model was included in the intercomparison, and consequently the accuracy of shelfy stream models as approximations of full-Stokes models remains to be determined in detail, especially during transients.

Published
2012
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9. Sensitivity of the Northeast Greenland Ice Stream to Geothermal Heat

Author

B. de Fleurian, Silje Smith-Johnsen, Kerim H. Nisancioglu, and Nicole Schlegel

Subjects
Geophysics, 010504 meteorology & atmospheric sciences, 13. Climate action, Ice stream, Geothermal heating, 14. Life underwater, 010502 geochemistry & geophysics, Atmospheric sciences, 01 natural sciences, Sensitivity (explosives), Geology, 0105 earth and related environmental sciences, Earth-Surface Processes
Abstract

Recent observations of ice flow surface velocities have helped improve our understanding of basal processes on Greenland and Antarctica, though these processes still constitute some of the largest uncertainties driving ice flow change today. The Northeast Greenland Ice Stream is driven largely by basal sliding, believed to be related to subglacial hydrology and the availability of heat. Characterization of the uncertainties associated with Northeast Greenland Ice Stream is crucial for constraining Greenland's potential contribution to sea level rise in the upcoming centuries. Here, we expand upon past work using the Ice Sheet System Model to quantify the uncertainties in models of the ice flow in the Northeast Greenland Ice Stream by perturbing the geothermal heat flux. Utilizing a subglacial hydrology model simulating sliding beneath the Greenland Ice Sheet, we investigate the sensitivity of the Northeast Greenland Ice Stream ice flow to various estimates of geothermal heat flux, and implications of basal heat flux uncertainties on modeling the hydrological processes beneath Greenland's major ice stream. We find that the uncertainty due to sliding at the bed is 10 times greater than the uncertainty associated with internal ice viscosity. Geothermal heat flux dictates the size of the area of the subglacial drainage system and its efficiency. The uncertainty of ice discharge from the Northeast Greenland Ice Stream to the ocean due to uncertainties in the geothermal heat flux is estimated at 2.10 Gt/yr. This highlights the urgency in obtaining better constraints on the highly uncertain subglacial hydrology parameters. publishedVersion

Published
2019

10. Ice Thickness and Bed Elevation of the Northern and Southern Patagonian Icefields

Author

Jeremie Mouginot, Yonggyu Gim, D. L. Kirchner, V. Martineau, G. Lenzano, Andrés Rivera, Eric Rignot, Rodrigo Zamora, B. de Fleurian, Xiaojian Li, Romain Millan, José Uribe, Institut des Géosciences de l’Environnement (IGE), Institut de Recherche pour le Développement (IRD)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), University of California [Irvine] (UC Irvine), University of California (UC), Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), Department of Earth System Science [Irvine] (ESS), University of California (UC)-University of California (UC), Department of Physics and Astronomy [Iowa City], University of Iowa [Iowa City], Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut de Recherche pour le Développement (IRD)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), University of California [Irvine] (UCI), University of California, and University of California-University of California

Subjects
ICE THICKNESS, 010504 meteorology & atmospheric sciences, [SDE.MCG]Environmental Sciences/Global Changes, PATAGONIAN ICEFIELDS, Elevation, 010502 geochemistry & geophysics, 01 natural sciences, RADAR DEPTH SOUNDER, Ice thickness, Geophysics, purl.org/becyt/ford/2 [https], ICE VOLUME, [SDE]Environmental Sciences, BEDROCK TOPOGRAPHY, General Earth and Planetary Sciences, AIRBORNE GRAVITY, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Geomorphology, Geology, ComputingMilieux_MISCELLANEOUS, purl.org/becyt/ford/2.11 [https], 0105 earth and related environmental sciences
Abstract

The Northern and Southern Patagonian Icefields are the largest ice masses in the Southern Hemisphere outside Antarctica, but their ice volume and bed topography are poorly known. Here, we combine airborne gravity data collected in 2012 and 2016, with radar data from the Warm Ice Experiment Sounder and Centro de Estudios Científicos's to map bed elevation and ice thickness in great detail. We perform a 3-D inversion of the gravity data constrained by radar-derived thickness and fjord bathymetry to infer bed elevation at 500-m spacing, with a precision of about 60 m. We detect deep glacial valleys with ice thickness exceeding 1,400 m and sectors below sea level on the western branch of Glaciar Pio XI, Occidental, between San Rafael and Colonia, and near Fitz Roy. We calculate an ice volume of 4,756 ± 923 km3 for Northern Patagonia Icefield and Southern Patagonia Icefield, or 40 times the volume of glaciers in the European Alps. Fil: Millan, R.. University of California at Irvine; Estados Unidos Fil: Rignot, E.. University of California; Estados Unidos. Jet Propulsion Laboratory; Estados Unidos. Centro de Estudios Científicos; Chile Fil: Rivera, A.. Centro de Estudios Científicos; Chile. Universidad de Chile; Chile Fil: Martineau, V.. University of California; Estados Unidos Fil: Mouginot, J.. University of California at Irvine; Estados Unidos Fil: Zamora, R.. Universidad de Chile; Chile. Centro de Estudios Científicos; Chile Fil: Uribe, J.. Centro de Estudios Científicos; Chile Fil: Lenzano, María Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina Fil: De Fleurian, B.. University of Bergen; Noruega Fil: Li, X.. University of California at Irvine; Estados Unidos Fil: Gim, Y.. Jet Propulsion Laboratory; Estados Unidos Fil: Kirchner, D.. University of Iowa; Estados Unidos

Published
2019

11. Modeling of ocean-induced ice melt rates of five west Greenland glaciers over the past two decades

Author

Y. Xu, Bernd Scheuchl, H. Seroussi, Mathieu Morlighem, Jeremie Mouginot, Eric Rignot, Dimitris Menemenlis, Ian Fenty, L. An, B. de Fleurian, C. Cai, X. Li, and M. R. van den Broeke

Subjects
geography, geography.geographical_feature_category, 010504 meteorology & atmospheric sciences, Ice stream, Future sea level, Antarctic sea ice, 010502 geochemistry & geophysics, Glacier morphology, 01 natural sciences, Ice shelf, Geophysics, Climatology, Sea ice, Melt pond, General Earth and Planetary Sciences, Ice sheet, Geology, 0105 earth and related environmental sciences
Abstract

High-resolution, three-dimensional simulations from the Massachusetts Institute of Technology general circulation model ocean model are used to calculate the subaqueous melt rate of the calving faces of Umiamako, Rinks, Kangerdlugssup, Store, and Kangilerngata glaciers, west Greenland, from 1992 to 2015. Model forcing is from monthly reconstructions of ocean state and ice sheet runoff. Results are analyzed in combination with observations of bathymetry, bed elevation, ice front retreat, and glacier speed. We calculate that subaqueous melt rates are 2–3 times larger in summer compared to winter and doubled in magnitude since the 1990s due to enhanced subglacial runoff and 1.6 ± 0.3°C warmer ocean temperature. Umiamako and Kangilerngata retreated rapidly in the 2000s when subaqueous melt rates exceeded the calving rates and ice front retreated to deeper bed elevation. In contrast, Store, Kangerdlugssup, and Rinks have remained stable because their subaqueous melt rates are 3–4 times lower than their calving rates, i.e., the glaciers are dominated by calving processes.

Published
2016

12. Two independent methods for mapping the grounding line of an outlet glacier - an example from the Astrolabe Glacier, Terre Adélie, Antarctica

Author

A. Drouet, Etienne Berthier, Jamin S. Greenbaum, Jeremie Mouginot, M. Sacchettini, Eric Rignot, Stéphane Garambois, Olivier Gagliardini, Geoffroy Durand, Fabien Gillet-Chaulet, John W. Holt, B. de Fleurian, Donald D. Blankenship, D. L. Kirchner, E. Le Meur, D. A. Young, Yonggyu Gim, Laboratoire de glaciologie et géophysique de l'environnement (LGGE), Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut des Sciences de la Terre (ISTerre), Université Joseph Fourier - Grenoble 1 (UJF)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR219-PRES Université de Grenoble-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), Cryosphère satelittaire (CRYO), Laboratoire d'études en Géophysique et océanographie spatiales (LEGOS), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Institute for Geophysics, University of Texas at Dallas [Richardson] (UT Dallas), Department of Earth System Science [Irvine] (ESS), University of California [Irvine] (UC Irvine), University of California (UC)-University of California (UC), Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), Department of Physics and Astronomy [Iowa City], University of Iowa [Iowa City], Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), University of California [Irvine] (UCI), University of California-University of California, Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS), Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-PRES Université de Grenoble-Institut de recherche pour le développement [IRD] : UR219-Institut national des sciences de l'Univers (INSU - CNRS)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Université Joseph Fourier - Grenoble 1 (UJF), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National d'Études Spatiales [Toulouse] (CNES)-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), and California Institute of Technology (CALTECH)-NASA

Subjects
010504 meteorology & atmospheric sciences, Astrolabe, 010502 geochemistry & geophysics, 01 natural sciences, law.invention, Physics::Geophysics, Position (vector), law, Satellite imagery, Geomorphology, lcsh:Environmental sciences, Physics::Atmospheric and Oceanic Physics, 0105 earth and related environmental sciences, Earth-Surface Processes, Water Science and Technology, lcsh:GE1-350, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, geography, geography.geographical_feature_category, business.industry, lcsh:QE1-996.5, Lead (sea ice), Glacier, Geodesy, lcsh:Geology, Line (geometry), Global Positioning System, Hydrostatic equilibrium, business, Geology
Abstract

The grounding line is a key element of coastal outlet glaciers, acting on their dynamics. Accurately knowing its position is fundamental for both modelling the glacier dynamics and establishing a benchmark for later change detection. Here we map the grounding line of the Astrolabe Glacier in East Antarctica (66°41' S, 140°05' E), using both hydrostatic and tidal methods. The first method is based on new surface and ice thickness data from which the line of buoyant floatation is found. The second method uses kinematic GPS measurements of the tidal response of the ice surface. By detecting the transitions where the ice starts to move vertically in response to the tidal forcing we determine control points for the grounding line position along GPS profiles. Employing a two-dimensional elastic plate model, we compute the rigid short-term behaviour of the ice plate and estimate the correction required to compare the kinematic GPS control points with the previously determined line of floatation. These two approaches show consistency and lead us to propose a grounding line for the Astrolabe Glacier that significantly deviates from the lines obtained so far from satellite imagery.

Published
2014

13. Two independent methods for mapping the grounding line of an outlet glacier – example from the Astrolabe Glacier, Terre Adélie, Antarctica

Author

E. Le Meur, M. Sacchettini, S. Garambois, E. Berthier, A. S. Drouet, G. Durand, D. Young, J. S. Greenbaum, D. D. Blankenship, J. W. Holt, E. Rignot, J. Mouginot, Y. Gim, D. Kirchner, B. de Fleurian, O. Gagliardini, and F. Gillet-Chaulet

Subjects
Physics::Atmospheric and Oceanic Physics, Physics::Geophysics
Abstract

The grounding line is a key element acting on the dynamics of coastal outlet glaciers. Knowing its position accurately is fundamental for both modelling the glacier dynamics and establishing a benchmark to which one can later refer in case of change. Here we map the grounding line of the Astrolabe Glacier in East Antarctica (66°41´ S; 140°05´ E), using hydrostatic and tidal methods. The first method is based on new surface and ice thickness data from which the line of buoyant flotation is found. We compare this hydrostatic map with kinematic GPS measurements of the tidal response of the ice surface. By detecting the transitions where the ice starts to move vertically in response to the tidal forcing we find control points for the grounding line position along GPS profiles. %If it can be shown that the long-term viscous mechanical behaviour of the ice slab validates the hydrostatic approach, mapping the grounding line from the ice supper surface displacements conversely requires correcting for the rigid elastic slab effect that dominates at tidal frequencies. With the help of a 2-dimensional elastic plate model, rigid elastic deviations are computed and applied to these control points. Once the extent of the grounding zone, the kinematic approach is consistent with the hydrostatic map. These two approaches lead us to propose a grounding line for the Astrolabe Glacier that significantly deviates from those obtained so far from satellite imagery.

Published
2013

14. A subglacial hydrological model dedicated to glacier sliding

Author

Thomas Zwinger, B. de Fleurian, Olivier Gagliardini, G. Durand, Peter Råback, E. Le Meur, and Douglas Mair

Subjects
geography, geography.geographical_feature_category, Glacier, Geomorphology, Geology
Abstract

The flow of glaciers and ice-streams is strongly influenced by the presence of water at the interface between ice and bedrock. In this paper, a hydrological model evaluating the subglacial water pressure is developed with the final aim of estimating the sliding velocities of glaciers. The global model fully couples the subglacial hydrology and the ice dynamics through a water-dependent friction law. The hydrological part of the model follows a double continuum approach which relies on the use of porous layers to compute water heads in inefficient and efficient drainage systems. This method has the advantage of a relatively low computational cost that would allow its application to large ice bodies such as Greenland or Antarctica ice-streams. The hydrological model has been implemented in the finite element code Elmer/Ice, which simultaneously computes the ice flow. Herein, we present an application to the Haut Glacier d'Arolla for which we have a large number of observations, making it well suited to the purpose of validating both the hydrology and ice flow model components. The selection of hydrological, under-determined parameters from a wide range of values is guided by comparison of the model results with available glacier observations. Once this selection has been performed, the coupling between subglacial hydrology and ice dynamics is undertaken throughout a melt season. Results indicate that this new modelling approach for subglacial hydrology is able to reproduce the broad temporal and spatial patterns of the observed subglacial hydrological system. Furthermore, the coupling with the ice dynamics shows good agreement with the observed spring speed-up.

Published
2013

15. Capabilities and performance of Elmer/Ice, a new generation ice-sheet model

Author

Carlos Martín, Olivier Gagliardini, G. Durand, Peter Råback, Juha Ruokolainen, Ralf Greve, Jonas Thies, Mika Malinen, Lionel Favier, Martina Schäfer, Hakime Seddik, M. Sacchettini, Fabien Gillet-Chaulet, Thomas Zwinger, and B. de Fleurian

Subjects
Matematik, geography, geography.geographical_feature_category, Meteorology, 010504 meteorology & atmospheric sciences, Ice stream, Flow (psychology), Isotropy, lcsh:QE1-996.5, Greenland ice sheet, Geophysics, Solver, 010502 geochemistry & geophysics, 01 natural sciences, Physics::Geophysics, Current (stream), Ice-sheet model, lcsh:Geology, 13. Climate action, Astrophysics::Earth and Planetary Astrophysics, Ice sheet, Mathematics, Physics::Atmospheric and Oceanic Physics, 0105 earth and related environmental sciences
Abstract

The Fourth IPCC Assessment Report concluded that ice sheet flow models, in their current state, were unable to provide accurate forecast for the increase of polar ice sheet discharge and the associated contribution to sea level rise. Since then, the glaciological community has undertaken a huge effort to develop and improve a new generation of ice flow models, and as a result a significant number of new ice sheet models have emerged. Among them is the parallel finite-element model Elmer/Ice, based on the open-source multi-physics code Elmer. It was one of the first full-Stokes models used to make projections for the evolution of the whole Greenland ice sheet for the coming two centuries. Originally developed to solve local ice flow problems of high mechanical and physical complexity, Elmer/Ice has today reached the maturity to solve larger-scale problems, earning the status of an ice sheet model. Here, we summarise almost 10 yr of development performed by different groups. Elmer/Ice solves the full-Stokes equations, for isotropic but also anisotropic ice rheology, resolves the grounding line dynamics as a contact problem, and contains various basal friction laws. Derived fields, like the age of the ice, the strain rate or stress, can also be computed. Elmer/Ice includes two recently proposed inverse methods to infer badly known parameters. Elmer is a highly parallelised code thanks to recent developments and the implementation of a block preconditioned solver for the Stokes system. In this paper, all these components are presented in detail, as well as the numerical performance of the Stokes solver and developments planned for the future.

Published
2013

16. Results of the Marine Ice Sheet Model Intercomparison Project, MISMIP

Author

Christian Schoof, G. H. Gudmundsson, David Pollard, Andreas Vieli, Victoria Lee, Daniel Goldberg, Rupert Gladstone, Laura Perichon, Frank Pattyn, Fuyuki Saito, Antony J. Payne, B. de Fleurian, Olivier Gagliardini, G. Durand, Philippe Huybrechts, Faezeh M. Nick, Oleg Rybak, Ed Bueler, Richard C. A. Hindmarsh, Earth System Sciences, Physical Geography, Geography, Laboratoire de Glaciologie, Université Libre de Bruxelles [Bruxelles] (ULB), Department of Earth and Ocean Sciences [Vancouver], University of British Columbia (UBC), British Antarctic Survey (BAS), Natural Environment Research Council (NERC), Department of Mathematics and Geophysical Institute, University of Alaska [Anchorage], Laboratoire de glaciologie et géophysique de l'environnement (LGGE), Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS), School of Geographical Sciences [Bristol], University of Bristol [Bristol], Courant Institute of Mathematical Sciences [New York] (CIMS), New York University [New York] (NYU), NYU System (NYU)-NYU System (NYU), Earth System Sciences & Department of Geography, Vrije Universiteit [Brussels] (VUB), Institute for Marine and Atmospheric Research [Utrecht] (IMAU), Utrecht University [Utrecht], Earth and Environmental Systems Institute, College of Earth and Mineral Sciences, Frontier Research Center for Global Change (FRCGC), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Department of Geography, Durham University, IceCube-Dyn, European Project: 226375,EC:FP7:ENV,FP7-ENV-2008-1,ICE2SEA(2009), Université libre de Bruxelles (ULB), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), Vrije Universiteit Brussel (VUB), Pennsylvania State University (Penn State), Penn State System-Penn State System, and Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Steady state (electronics), 010504 meteorology & atmospheric sciences, Discretization, Meteorology, Ice sheet modeling, Flux, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, F800, 010502 geochemistry & geophysics, 01 natural sciences, lcsh:Environmental sciences, 0105 earth and related environmental sciences, Earth-Surface Processes, Water Science and Technology, lcsh:GE1-350, geography, geography.geographical_feature_category, Adaptive mesh refinement, lcsh:QE1-996.5, Mechanics, Glaciologie, Grid, lcsh:Geology, Ice-sheet model, Line (geometry), Ice sheet, Geology
Abstract

Predictions of marine ice-sheet behaviour require models that are able to robustly simulate grounding line migration. We present results of an intercomparison exercise for marine ice-sheet models. Verification is effected by comparison with approximate analytical solutions for flux across the grounding line using simplified geometrical configurations (no lateral variations, no effects of lateral buttressing). Unique steady state grounding line positions exist for ice sheets on a downward sloping bed, while hysteresis occurs across an overdeepened bed, and stable steady state grounding line positions only occur on the downward-sloping sections. Models based on the shallow ice approximation, which does not resolve extensional stresses, do not reproduce the approximate analytical results unless appropriate parameterizations for ice flux are imposed at the grounding line. For extensional-stress resolving "shelfy stream" models, differences between model results were mainly due to the choice of spatial discretization. Moving grid methods were found to be the most accurate at capturing grounding line evolution, since they track the grounding line explicitly. Adaptive mesh refinement can further improve accuracy, including fixed grid models that generally perform poorly at coarse resolution. Fixed grid models, with nested grid representations of the grounding line, are able to generate accurate steady state positions, but can be inaccurate over transients. Only one full-Stokes model was included in the intercomparison, and consequently the accuracy of shelfy stream models as approximations of full-Stokes models remains to be determined in detail, especially during transients. © 2012 Author(s)., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
2012

17. Marine ice sheet dynamics: Hysteresis and neutral equilibrium

Author

B. de Fleurian, Thomas Zwinger, Olivier Gagliardini, E. Le Meur, Gaël Durand, Laboratoire de glaciologie et géophysique de l'environnement (LGGE), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), Scientific Computing Ltd (CSC), ANR-06-VULN-0016,DACOTA,Dynamique des glaciers côtiers et rôle sur le bilan de masse global de l'Antarctique zone atelier du glacier de l'Astrolabe, Terre Adélie(2006), Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS), and DACOTA project (ANR-06-VULN-016-01),DACOTA project (ANR-06-VULN-016-01)

Subjects
Atmospheric Science, Ice-sheet dynamics, 010504 meteorology & atmospheric sciences, 0207 environmental engineering, Soil Science, 02 engineering and technology, Aquatic Science, Pressure ridge, Oceanography, 01 natural sciences, Physics::Geophysics, Sea ice growth processes, Geochemistry and Petrology, Earth and Planetary Sciences (miscellaneous), Sea ice, Geotechnical engineering, 14. Life underwater, marine ice sheet, [SDU.STU.GL]Sciences of the Universe [physics]/Earth Sciences/Glaciology, 020701 environmental engineering, Physics::Atmospheric and Oceanic Physics, 0105 earth and related environmental sciences, Earth-Surface Processes, Water Science and Technology, geography, geography.geographical_feature_category, Ecology, Bedrock, Paleontology, Forestry, Glacier, Mechanics, Boundary layer, Geophysics, 13. Climate action, Space and Planetary Science, Astrophysics::Earth and Planetary Astrophysics, Ice sheet, full Stokes modeling, grounding line, Geology
Abstract

International audience; The stability of marine ice sheets and outlet glaciers is mostly controlled by the dynamics of their grounding line, i.e., where the bottom contact of the ice changes from bedrock or till to ocean water. The last report of the Intergovernmental Panel on Climate Change has clearly underlined the poor ability of models to capture the dynamics of outlet glaciers. Here we present computations of grounding line dynamics on the basis of numerical solutions of the full Stokes equations for ice velocity, coupled with the evolution of the air ice– and sea ice–free interfaces. The grounding line position is determined by solving the contact problem between the ice and a rigid bedrock using the finite element code Elmer. Results of the simulations show that marine ice sheets are unstable on upsloping beds and undergo hysteresis under perturbation of ice viscosity, confirming conclusions from boundary layer theory. The present approach also indicates that a 2-D unconfined marine ice sheet sliding over a downsloping bedrock does not exhibit neutral equilibrium. It is shown that mesh resolution around the grounding line is a crucial issue. A very fine grid size (

Published
2009

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