Articles | Volume 16, issue 7
https://doi.org/10.5194/tc-16-2683-2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-16-2683-2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
08 Jul 2022
Research article |
| 08 Jul 2022
| 08 Jul 2022
Modeling enhanced firn densification due to strain softening
Falk M. Oraschewski
CORRESPONDING AUTHOR
Department of Geosciences, University of Tübingen, Tübingen, Germany
Physics of Ice, Climate, and Earth, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
Aslak Grinsted
Physics of Ice, Climate, and Earth, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
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Falk M. Oraschewski, Inka Koch, M. Reza Ershadi, Jonathan Hawkins, Olaf Eisen, and Reinhard Drews
EGUsphere, https://doi.org/10.5194/egusphere-2023-2731, https://doi.org/10.5194/egusphere-2023-2731, 2023
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Mountain glaciers have a layered structure which contains information about past snow accumulation and ice flow. Using ground-looking radar instruments, the internal structure can be observed to obtain this information. In the deeper parts of the glacier, detecting layers is often difficult. In this study we present a new approach to observe deep englacial layers in an Alpine glacier (Colle Gnifetti, Switzerland/Italy) and investigate why these deeper layers are harder to detect at this site.
Falk M. Oraschewski, Inka Koch, M. Reza Ershadi, Jonathan Hawkins, Olaf Eisen, and Reinhard Drews
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Mountain glaciers have a layered structure which contains information about past snow accumulation and ice flow. Using ground-looking radar instruments, the internal structure can be observed to obtain this information. In the deeper parts of the glacier, detecting layers is often difficult. In this study we present a new approach to observe deep englacial layers in an Alpine glacier (Colle Gnifetti, Switzerland/Italy) and investigate why these deeper layers are harder to detect at this site.
Aslak Grinsted, Nicholas Mossor Rathmann, Ruth Mottram, Anne Munck Solgaard, Joachim Mathiesen, and Christine Schøtt Hvidberg
EGUsphere, https://doi.org/10.5194/egusphere-2023-1957, https://doi.org/10.5194/egusphere-2023-1957, 2023
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Ice fracture can cause glacier crevassing and calving. These natural hazards can also modulate the flow and evolution of ice sheets. In a new study, Grinsted and coauthors use a new high-resolution dataset to determine a new failure criterion for glacier ice. Surprisingly, the strength of ice depends on the mode of deformation, and this has potential implications for the currently-used flow law of ice.
Ann-Sofie Priergaard Zinck and Aslak Grinsted
The Cryosphere, 16, 1399–1407, https://doi.org/10.5194/tc-16-1399-2022, https://doi.org/10.5194/tc-16-1399-2022, 2022
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The Müller Ice Cap will soon set the scene for a new drilling project. To obtain an ice core with stratified layers and a good time resolution, thickness estimates are necessary for the planning. Here we present a new and fast method of estimating ice thicknesses from sparse data and compare it to an existing ice flow model. We find that the new semi-empirical method is insensitive to mass balance, is computationally fast, and provides good fits when compared to radar measurements.
Tamara Annina Gerber, Christine Schøtt Hvidberg, Sune Olander Rasmussen, Steven Franke, Giulia Sinnl, Aslak Grinsted, Daniela Jansen, and Dorthe Dahl-Jensen
The Cryosphere, 15, 3655–3679, https://doi.org/10.5194/tc-15-3655-2021, https://doi.org/10.5194/tc-15-3655-2021, 2021
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We simulate the ice flow in the onset region of the Northeast Greenland Ice Stream to determine the source area and past accumulation rates of ice found in the EastGRIP ice core. This information is required to correct for bias in ice-core records introduced by the upstream flow effects. Our results reveal that the increasing accumulation rate with increasing upstream distance is predominantly responsible for the constant annual layer thicknesses observed in the upper 900 m of the ice core.
Aslak Grinsted and Jens Hesselbjerg Christensen
Ocean Sci., 17, 181–186, https://doi.org/10.5194/os-17-181-2021, https://doi.org/10.5194/os-17-181-2021, 2021
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As we warm our planet, oceans expand, ice on land melts, and sea levels rise. On century timescales, we find that the sea level response to warming can be characterized by a single metric: the transient sea level sensitivity. Historical sea level exhibits substantially higher sensitivity than model-based estimates of future climates in authoritative climate assessments, implying recent projections could well underestimate the likely sea level rise by the end of this century.
Christine S. Hvidberg, Aslak Grinsted, Dorthe Dahl-Jensen, Shfaqat Abbas Khan, Anders Kusk, Jonas Kvist Andersen, Niklas Neckel, Anne Solgaard, Nanna B. Karlsson, Helle Astrid Kjær, and Paul Vallelonga
The Cryosphere, 14, 3487–3502, https://doi.org/10.5194/tc-14-3487-2020, https://doi.org/10.5194/tc-14-3487-2020, 2020
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The Northeast Greenland Ice Stream (NEGIS) extends around 600 km from its onset in the interior of Greenland to the coast. Several maps of surface velocity and topography in Greenland exist, but accuracy is limited due to the lack of validation data. Here we present results from a 5-year GPS survey in an interior section of NEGIS. We use the data to assess a list of satellite-derived ice velocity and surface elevation products and discuss the implications for the ice stream flow in the area.
Related subject area
Discipline: Ice sheets | Subject: Ice Physics
Failure strength of glacier ice inferred from Greenland crevasses
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Ice fabrics in two-dimensional flows: beyond pure and simple shear
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Observation of an optical anisotropy in the deep glacial ice at the geographic South Pole using a laser dust logger
Using a composite flow law to model deformation in the NEEM deep ice core, Greenland – Part 1: The role of grain size and grain size distribution on deformation of the upper 2207 m
Using a composite flow law to model deformation in the NEEM deep ice core, Greenland – Part 2: The role of grain size and premelting on ice deformation at high homologous temperature
The role of subtemperate slip in thermally driven ice stream margin migration
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Aslak Grinsted, Nicholas Mossor Rathmann, Ruth Mottram, Anne Munck Solgaard, Joachim Mathiesen, and Christine Schøtt Hvidberg
EGUsphere, https://doi.org/10.5194/egusphere-2023-1957, https://doi.org/10.5194/egusphere-2023-1957, 2023
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Ice fracture can cause glacier crevassing and calving. These natural hazards can also modulate the flow and evolution of ice sheets. In a new study, Grinsted and coauthors use a new high-resolution dataset to determine a new failure criterion for glacier ice. Surprisingly, the strength of ice depends on the mode of deformation, and this has potential implications for the currently-used flow law of ice.
Sheng Fan, David J. Prior, Brent Pooley, Hamish Bowman, Lucy Davidson, David Wallis, Sandra Piazolo, Chao Qi, David L. Goldsby, and Travis F. Hager
The Cryosphere, 17, 3443–3459, https://doi.org/10.5194/tc-17-3443-2023, https://doi.org/10.5194/tc-17-3443-2023, 2023
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The microstructure of ice controls the behaviour of polar ice flow. Grain growth can modify the microstructure of ice; however, its processes and kinetics are poorly understood. We conduct grain-growth experiments on synthetic and natural ice samples at 0 °C. Microstructural data show synthetic ice grows continuously with time. In contrast, natural ice does not grow within a month. The inhibition of grain growth in natural ice is largely contributed by bubble pinning at ice grain boundaries.
Daniel H. Richards, Samuel S. Pegler, and Sandra Piazolo
The Cryosphere, 16, 4571–4592, https://doi.org/10.5194/tc-16-4571-2022, https://doi.org/10.5194/tc-16-4571-2022, 2022
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Understanding the orientation of ice grains is key for predicting ice flow. We explore the evolution of these orientations using a new efficient model. We present an exploration of the patterns produced under a range of temperatures and 2D deformations, including for the first time a universal regime diagram. We do this for deformations relevant to ice sheets but not studied in experiments. These results can be used to understand drilled ice cores and improve future modelling of ice sheets.
M. Reza Ershadi, Reinhard Drews, Carlos Martín, Olaf Eisen, Catherine Ritz, Hugh Corr, Julia Christmann, Ole Zeising, Angelika Humbert, and Robert Mulvaney
The Cryosphere, 16, 1719–1739, https://doi.org/10.5194/tc-16-1719-2022, https://doi.org/10.5194/tc-16-1719-2022, 2022
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Radio waves transmitted through ice split up and inform us about the ice sheet interior and orientation of single ice crystals. This can be used to infer how ice flows and improve projections on how it will evolve in the future. Here we used an inverse approach and developed a new algorithm to infer ice properties from observed radar data. We applied this technique to the radar data obtained at two EPICA drilling sites, where ice cores were used to validate our results.
Pavel Talalay, Yazhou Li, Laurent Augustin, Gary D. Clow, Jialin Hong, Eric Lefebvre, Alexey Markov, Hideaki Motoyama, and Catherine Ritz
The Cryosphere, 14, 4021–4037, https://doi.org/10.5194/tc-14-4021-2020, https://doi.org/10.5194/tc-14-4021-2020, 2020
Maria Zeitz, Anders Levermann, and Ricarda Winkelmann
The Cryosphere, 14, 3537–3550, https://doi.org/10.5194/tc-14-3537-2020, https://doi.org/10.5194/tc-14-3537-2020, 2020
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The flow of ice drives mass losses in the large ice sheets. Sea-level rise projections rely on ice-sheet models, solving the physics of ice flow and melt. Unfortunately the parameters in the physics of flow are uncertain. Here we show, in an idealized setup, that these uncertainties can double flow-driven mass losses within the possible range of parameters. It is possible that this uncertainty carries over to realistic sea-level rise projections.
Martin Rongen, Ryan Carlton Bay, and Summer Blot
The Cryosphere, 14, 2537–2543, https://doi.org/10.5194/tc-14-2537-2020, https://doi.org/10.5194/tc-14-2537-2020, 2020
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We report on the observation of a directional anisotropy in the intensity of backscattered light. The measurement was performed using a laser dust logger in the SPC14 drill hole at the geographic South Pole. We find the anisotropy axis to be compatible with the ice flow direction. It is discussed in comparison to a similar anisotropy observed by the IceCube Neutrino Observatory. In future, the measurement principle may provide a continuous record of crystal properties along entire drill holes.
Ernst-Jan N. Kuiper, Ilka Weikusat, Johannes H. P. de Bresser, Daniela Jansen, Gill M. Pennock, and Martyn R. Drury
The Cryosphere, 14, 2429–2448, https://doi.org/10.5194/tc-14-2429-2020, https://doi.org/10.5194/tc-14-2429-2020, 2020
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A composite flow law model applied to crystal size distributions from the NEEM deep ice core predicts that fine-grained layers in ice from the last Glacial period localize deformation as internal shear zones in the Greenland ice sheet deforming by grain-size-sensitive creep. This prediction is consistent with microstructures in Glacial age ice.
Ernst-Jan N. Kuiper, Johannes H. P. de Bresser, Martyn R. Drury, Jan Eichler, Gill M. Pennock, and Ilka Weikusat
The Cryosphere, 14, 2449–2467, https://doi.org/10.5194/tc-14-2449-2020, https://doi.org/10.5194/tc-14-2449-2020, 2020
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Fast ice flow occurs in deeper parts of polar ice sheets, driven by high stress and high temperatures. Above 262 K ice flow is further enhanced, probably by the formation of thin melt layers between ice crystals. A model applying an experimentally derived composite flow law, using temperature and grain size values from the deepest 540 m of the NEEM ice core, predicts that flow in fine-grained layers is enhanced by a factor of 10 compared to coarse-grained layers in the Greenland ice sheet.
Marianne Haseloff, Christian Schoof, and Olivier Gagliardini
The Cryosphere, 12, 2545–2568, https://doi.org/10.5194/tc-12-2545-2018, https://doi.org/10.5194/tc-12-2545-2018, 2018
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The widths of the Siple Coast ice streams evolve on decadal to centennial timescales. We investigate how the rate of thermally driven ice stream widening depends on heat dissipation in the ice stream margin and at the bed, and on the inflow of cold ice from the ice ridge. As determining the migration rate requires resolving heat transfer processes on very small scales, we derive a parametrization of the migration rate in terms of parameters that are available from large-scale model outputs.
Johanna Kerch, Anja Diez, Ilka Weikusat, and Olaf Eisen
The Cryosphere, 12, 1715–1734, https://doi.org/10.5194/tc-12-1715-2018, https://doi.org/10.5194/tc-12-1715-2018, 2018
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We investigate the effect of crystal anisotropy on seismic velocities in glacier ice by calculating seismic phase velocities using the exact c axis angles to describe the crystal orientations in ice-core samples for an alpine and a polar ice core. Our results provide uncertainty estimates for earlier established approximative calculations. Additionally, our findings highlight the variation in seismic velocity at non-vertical incidence as a function of the horizontal azimuth of the seismic plane.
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Short summary
Old snow (denoted as firn) accumulates in the interior of ice sheets and gets densified into glacial ice. Typically, this densification is assumed to only depend on temperature and accumulation rate. However, it has been observed that stretching of the firn by horizontal flow also enhances this process. Here, we show how to include this effect in classical firn models. With the model we confirm that softening of the firn controls firn densification in areas with strong horizontal stretching.
Old snow (denoted as firn) accumulates in the interior of ice sheets and gets densified into...
