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  • 1
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    Elastic deformation plays a non-negligible role in Greenland’s outlet glacier flow (2021)
    Christmann, Julia ; Helm, Veit ; Khan, Shfaqat Abbas ; [et al.]
    Nature Publishing Group UK
    Details
    Publication Date: 2023-11-13
    Description: Future projections of global mean sea level change are uncertain, partly because of our limited understanding of the dynamics of Greenland’s outlet glaciers. Here we study Nioghalvfjerdsbræ, an outlet glacier of the Northeast Greenland Ice Stream that holds 1.1 m sea-level equivalent of ice. We use GPS observations and numerical modelling to investigate the role of tides as well as the elastic contribution to glacier flow. We find that ocean tides alter the basal lubrication of the glacier up to 10 km inland of the grounding line, and that their influence is best described by a viscoelastic rather than a viscous model. Further inland, sliding is the dominant mechanism of fast glacier motion, and the ice flow induces persistent elastic strain. We conclude that elastic deformation plays a role in glacier flow, particularly in areas of steep topographic changes and fast ice velocities.
    Description: Ice flow dynamics in Greenland’s outlet glaciers are influenced by elastic deformation, both in the area of tidal influence up to 14 km inland from the grounding line and further upstream, suggest analyses of GPS observations and numerical simulations.
    Description: Bundesministerium für Bildung und Forschung (Federal Ministry of Education and Research) https://doi.org/10.13039/501100002347
    Description: European Union’s Horizon 2020 Research and Innovation Programme
    Description: https://doi.org/10.1594/PANGAEA.928940
    Description: https://nsidc.org/data/IDBMG4
    Description: https://gitlab.awi.de/jchristm/viscoelastic-79ng-greenland
    Description: https://doi.org/10.5281/zenodo.5507115
    Description: https://doi.org/10.5281/zenodo.5506953
    Keywords: ddc:551.31 ; Climate change ; Cryospheric science ; Hydrology
    Language: English
    Type: doc-type:article
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    CITATION GEO-LEO
  • 2
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    Design and results of the ice sheet model initialisation experiments initMIP-Greenland: an ISMIP6 intercomparison (2018)
    Copernicus Publications (EGU)
    In:  The Cryosphere, 12 (4). pp. 1433-1460.
    Details
    Publication Date: 2018-12-17
    Description: Earlier large-scale Greenland ice sheet sea-level projections (e.g. those run during the ice2sea and SeaRISE initiatives) have shown that ice sheet initial conditions have a large effect on the projections and give rise to important uncertainties. The goal of this initMIP-Greenland intercomparison exercise is to compare, evaluate, and improve the initialisation techniques used in the ice sheet modelling community and to estimate the associated uncertainties in modelled mass changes. initMIP-Greenland is the first in a series of ice sheet model intercomparison activities within ISMIP6 (the Ice Sheet Model Intercomparison Project for CMIP6), which is the primary activity within the Coupled Model Intercomparison Project Phase 6 (CMIP6) focusing on the ice sheets. Two experiments for the large-scale Greenland ice sheet have been designed to allow intercomparison between participating models of (1) the initial present-day state of the ice sheet and (2) the response in two idealised forward experiments. The forward experiments serve to evaluate the initialisation in terms of model drift (forward run without additional forcing) and in response to a large perturbation (prescribed surface mass balance anomaly); they should not be interpreted as sea-level projections. We present and discuss results that highlight the diversity of data sets, boundary conditions, and initialisation techniques used in the community to generate initial states of the Greenland ice sheet. We find good agreement across the ensemble for the dynamic response to surface mass balance changes in areas where the simulated ice sheets overlap but differences arising from the initial size of the ice sheet. The model drift in the control experiment is reduced for models that participated in earlier intercomparison exercises.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.5194/tc-12-1433-2018
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Simulation of the future sea level contribution of Greenland with a new glacial system model (2018)
    Copernicus Publications (EGU)
    In:  The Cryosphere Discussions . pp. 1-37.
    Details
    Publication Date: 2018-09-03
    Description: We introduce the coupled model of the Greenland glacial system IGLOO 1.0, including the polythermal ice sheet model SICOPOLIS (version 3.3) with hybrid dynamics, the model of basal hydrology HYDRO and a parameterization of submarine melt for marine-terminated outlet glaciers. Aim of this glacial system model is to gain a better understanding of the processes important for the future contribution of the Greenland ice sheet to sea level rise under future climate change scenarios. The ice sheet is initialized via a relaxation towards observed surface elevation, imposing the palaeo-surface temperature over the last glacial cycle. As a present-day reference, we use the 1961-1990 standard climatology derived from simulations of the regional atmosphere model MAR with ERA reanalysis boundary conditions. For the palaeo-part of the spin-up, we add the temperature anomaly derived from the GRIP ice core to the years 1961–1990 average surface temperature field. For our projections, we apply surface temperature and surface mass balance anomalies derived from RCP 4.5 and RCP 8.5 scenarios created by MAR with boundary conditions from simulations with three CMIP5 models. The hybrid ice sheet model is fully coupled with the model of basal hydrology. With this model and the MAR scenarios, we perform simulations to estimate the contribution of the Greenland ice sheet to future sea level rise until the end of the 21st and 23rd centuries. Further on, the impact of elevation-surface mass balance feedback, introduced via the MAR data, on future sea level rise is inspected. In our projections, we found the Greenland ice sheet to contribute to global sea level rise between 1.9 and 13.0cm until the year 2100 and between 3.5 and 76.4cm until the year 2300, including our simulated additional sea level rise due to elevation-surface mass balance feedback. Translated into additional sea level rise, the strength of this feedback in the year 2100 varies from 0.4 to 1.7cm, and in the year 2300 it ranges from 1.7 to 21.8cm. Additionally, taking Helheim and Store Glaciers as examples, we investigate the role of ocean warming and surface runoff change for the melting of outlet glaciers. It shows that ocean temperature and subglacial discharge are about equally important for the melting of the examined outlet glaciers.
    Type: Article , NonPeerReviewed
    Format: text
    DOI: 10.5194/tc-2018-23
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    OceanRep: Article in a Scientific Journal - without review
  • 4
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    Results of the third Marine Ice Sheet Model Intercomparison Project (MISMIP+) (2020)
    Copernicus Publications (EGU)
    Details
    Publication Date: 2023-01-04
    Description: We present the result of the third Marine Ice Sheet Intercomparison project, MISMIP+. MISMIP+ is intended to be a test of ice flow models which include fast sliding marine ice streams and floating ice shelves and in particular a treatment of viscous stress that is sufficient for buttressing, where upstream ice flow is restrained by a downstream ice shelf. A set of idealized experiments test the models in circumstances where buttressing contributes to a stable steady state, and where a reduction in that buttressing causes ice stream acceleration, thinning, and grounding line retreat. We find that the most important distinction between models in this particular type of simulation is in the treatment of sliding at the bed, with other distinctions – notably the difference between the simpler and more complete treatments of englacial stress, but also the differences between numerical methods – taking a secondary role.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Projected land ice contributions to twenty-first-century sea level rise (2021)
    Nature Research
    Details
    Publication Date: 2024-02-07
    Description: The land ice contribution to global mean sea level rise has not yet been predicted1 using ice sheet and glacier models for the latest set of socio-economic scenarios, nor using coordinated exploration of uncertainties arising from the various computer models involved. Two recent international projects generated a large suite of projections using multiple models2,3,4,5,6,7,8, but primarily used previous-generation scenarios9 and climate models10, and could not fully explore known uncertainties. Here we estimate probability distributions for these projections under the new scenarios11,12 using statistical emulation of the ice sheet and glacier models. We find that limiting global warming to 1.5 degrees Celsius would halve the land ice contribution to twenty-first-century sea level rise, relative to current emissions pledges. The median decreases from 25 to 13 centimetres sea level equivalent (SLE) by 2100, with glaciers responsible for half the sea level contribution. The projected Antarctic contribution does not show a clear response to the emissions scenario, owing to uncertainties in the competing processes of increasing ice loss and snowfall accumulation in a warming climate. However, under risk-averse (pessimistic) assumptions, Antarctic ice loss could be five times higher, increasing the median land ice contribution to 42 centimetres SLE under current policies and pledges, with the 95th percentile projection exceeding half a metre even under 1.5 degrees Celsius warming. This would severely limit the possibility of mitigating future coastal flooding. Given this large range (between 13 centimetres SLE using the main projections under 1.5 degrees Celsius warming and 42 centimetres SLE using risk-averse projections under current pledges), adaptation planning for twenty-first-century sea level rise must account for a factor-of-three uncertainty in the land ice contribution until climate policies and the Antarctic response are further constrained.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Remotely sensed surface velocities, Lagrangian basal melt rates, terminus positions, grounding lines as well as modelling results of Peterman Glacier (northern Greenland) (2018)
    PANGAEA
    In:  Supplement to: Rückamp, Martin; Neckel, Niklas; Berger, Sophie; Humbert, Angelika; Helm, Veit (2019): Calving Induced Speedup of Petermann Glacier. Journal of Geophysical Research-Earth Surface, https://doi.org/10.1029/2018JF004775
    Details
    Publication Date: 2023-03-16
    Description: This study assesses the response on ice dynamics of Petermann Glacier, a major outlet glacier in northern Greenland, to the 2012 and a possible future calving event. So far Petermann Glacier has been believed to be dynamically stable as another large calving event in 2010 had no significant impact on flow velocity or grounding line retreat. By analyzing a time series of remotely sensed surface velocities, we find an average acceleration of 10% between winter 2011/2012 and winter 2016/2017. This increase in surface velocity is not linear but can be separated into two parts, starting in 2012 and 2016 respectively. By conducting modelling experiments, we show that the first speed-up can be directly connected to the 2012 calving event, while the second speed-up is not captured. However, on recent remote sensing imagery newly developing fractures are clearly visible ~12,km upstream from the terminus, propagating from the eastern fjord wall to the center of the ice tongue, indicating a possible future calving event. By including these fracture zones as a new terminus position in the modelling domain we are able to reproduce the second speed-up, suggesting that surface velocities remain on the 2016/2017 level after the anticipated calving event. This indicates that, from a dynamical point of view, the terminus region has already detached from the main ice tongue.
    Keywords: AWI_Glac; File format; File name; File size; Glaciology @ AWI; North Greenland; Petermann_Glacier; RADAR; Radar profile; Uniform resource locator/link to file
    Type: Dataset
    Format: text/tab-separated-values, 72 data points
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    DATA PANGAEA
  • 7
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    Modelling calving front dynamics using a level-set method: application to Jakobshavn Isbræ, West Greenland, links model results in MATLAB format (2016)
    PANGAEA
    In:  Supplement to: Bondzio, Johannes H; Seroussi, Hélène; Morlighem, Mathieu; Kleiner, Thomas; Rückamp, Martin; Humbert, Angelika; Larour, Eric Y (2016): Modelling calving front dynamics using a level-set method: application to Jakobshavn Isbræ, West Greenland. The Cryosphere, 10(2), 497-510, https://doi.org/10.5194/tc-10-497-2016
    Details
    Publication Date: 2023-01-13
    Description: Calving is a major mechanism of ice discharge of the Antarctic and Greenland ice sheets, and a change in calving front position affects the entire stress regime of marine terminating glaciers. The representation of calving front dynamics in a 2-D or 3-D ice sheet model remains non-trivial. Here, we present the theoretical and technical framework for a level-set method, an implicit boundary tracking scheme, which we implement into the Ice Sheet System Model (ISSM). This scheme allows us to study the dynamic response of a drainage basin to user-defined calving rates. We apply the method to Jakobshavn Isbræ, a major marine terminating outlet glacier of the West Greenland Ice Sheet. The model robustly reproduces the high sensitivity of the glacier to calving, and we find that enhanced calving triggers significant acceleration of the ice stream. Upstream acceleration is sustained through a combination of mechanisms. However, both lateral stress and ice influx stabilize the ice stream. This study provides new insights into the ongoing changes occurring at Jakobshavn Isbræ and emphasizes that the incorporation of moving boundaries and dynamic lateral effects, not captured in flow-line models, is key for realistic model projections of sea level rise on centennial timescales.
    Keywords: Jakobshavn_Isbræ_drainage_basin; West Greenland
    Type: Dataset
    Format: application/zip, 469.2 MBytes
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    DATA PANGAEA
  • 8
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    Present-day King George Island ice cap geometry measured by ground penetrating radar in 2008/09 (2011)
    PANGAEA
    In:  Supplement to: Rückamp, Martin; Blindow, Norbert (2011): King George Island ice cap geometry updated with airborne GPR measurements. Earth System Science Data, 4(1), 23-30, https://doi.org/10.5194/essd-4-23-2012
    Details
    Publication Date: 2023-10-28
    Description: We present a consistent data set for the ice thickness, the bedrock topography and the ice surface topography of the King George Island ice cap (Arctowski Icefield and the adjacent central part). The data set is composed of groundbased and airborne Ground Penetrating Radar (GPR) and differential GPS (DGPS) measurements, obtained during several field campaigns. The data set incorporates groundbased measurements in the safely accessible inner parts and airborne measurements in the heavily crevassed coastal areas of the ice cap. In particular, the inclusion of airborne GPR measurements with the 30MHz BGR-P30-System developed at the Institute of Geophysics (University of Münster) completes the picture of the ice geometry substantially. The compiled digital elevation model of the bedrock shows a rough, highly variable topography with pronounced valleys, ridges, and troughs. The mean ice thickness is approx. 238m, with a maximum value of approx. 400m in the surveyed area. Noticeable are bounded areas in the bedrock topography below sea level where marine based ice exists.
    Keywords: ELEVATION; Elevation 2; Ground-penetrating radar (GPR); Ice thickness, glacier; King_George_Island; King George Island, Antarctic Peninsula; LATITUDE; LONGITUDE; Priority Programme 1158 Antarctic Research with Comparable Investigations in Arctic Sea Ice Areas; SPP1158; UTM Easting, Universal Transverse Mercator; UTM Northing, Universal Transverse Mercator; UTM Zone, Universal Transverse Mercator
    Type: Dataset
    Format: text/tab-separated-values, 960475 data points
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    DATA PANGAEA
  • 9
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    Mass balance measurements on King George Island ice cap in 2007 and 2008 (2011)
    PANGAEA
    In:  Supplement to: Rückamp, Martin; Braun, Matthias Holger; Suckro, Sonja K; Blindow, Norbert (2011): Observed glacial changes on the King George Island ice cap, Antarctica, in the last decade. Global and Planetary Change, 79(1-2), 99-109, https://doi.org/10.1016/j.gloplacha.2011.06.009
    Details
    Publication Date: 2023-10-28
    Description: The Antarctic Peninsula has been identified as a region of rapid on-going climate change with impacts on the cryosphere. The knowledge of glacial changes and freshwater budgets resulting from intensified glacier melt is an important boundary condition for many biological and integrated earth system science approaches. We provide a case study on glacier and mass balance changes for the ice cap of King George Island. The area loss between 2000 and 2008 amounted to about 20 km**2 (about 1.6% of the island area) and compares to glacier retreat rates observed in previous years. Measured net accumulation rates for two years (2007 and 2008) show a strong interannual variability with maximum net accumulation rates of 4950 mm w.e./a and 3184 mm w.e./a, respectively. These net accumulation rates are at least 4 times higher than reported mean values (1926-95) from an ice core. An elevation dependent precipitation rate of 343 mm w.e./a (2007) and 432 mm w.e./a (2008) per 100 m elevation increase was observed. Despite these rather high net accumulation rates on the main ice cap, consistent surface lowering was observed at elevations below 270 m above ellipsoid over an 11-year period. These DGPS records reveal a linear dependence of surface lowering with altitude with a maximum annual surface lowering rate of 1.44 m/a at 40 m and -0.20 m/a at 270 m above ellipsoid. These results fit well to observations by other authors and surface lowering rates derived from the ICESat laser altimeter. Assuming that climate conditions of the past 11 years continue, the small ice cap of Bellingshausen Dome will disappear in about 285 years.
    Keywords: DATE/TIME; ELEVATION; King_George_Island; King George Island, Antarctic Peninsula; LATITUDE; LONGITUDE; Mass balance in water equivalent per year; Priority Programme 1158 Antarctic Research with Comparable Investigations in Arctic Sea Ice Areas; SPP1158; UTM Easting, Universal Transverse Mercator; UTM Northing, Universal Transverse Mercator; UTM Zone, Universal Transverse Mercator
    Type: Dataset
    Format: text/tab-separated-values, 124 data points
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    DATA PANGAEA
  • 10
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    Measured ice surface velocities on the King George Island ice cap with DGPS (2012)
    PANGAEA
    In:  Supplement to: Rückamp, Martin; Blindow, Norbert; Suckro, Sonja K; Braun, Matthias Holger; Humbert, Angelika (2010): Dynamics of the ice cap on King George Island, Antarctica: field measurements and numerical simulations. Annals of Glaciology, 51(55), 80-90, https://doi.org/10.3189/172756410791392817
    Details
    Publication Date: 2023-10-28
    Description: King George Island is located at the northern tip of the Antarctic Peninsula, which is influenced by maritime climate conditions. The observed mean annual air temperature at sea level is -2.4°C. Thus, the ice cap is regarded as sensitive to changing climatic conditions. Ground-penetrating radar surveys indicate a partly temperate ice cap with an extended water layer at the firn/ice transition of the up to 700 m high ice cap. Measured firn temperatures are close to 0°C at the higher elevations, and they differ considerably from the measured mean annual air temperature. The aim of this paper is to present ice-flow dynamics by means of observations and simulations of the flow velocities. During several field campaigns from 1997/98 to 2008/09, ice surface velocities were derived with repeated differential GPS measurements. Ice velocities vary from 0.7 m/a at the dome to 112.1 m/a along steep slopes. For the western part of the ice cap a three-dimensional diagnostic full-Stokes model was applied to calculate ice flow. Parameters of the numerical model were identified with respect to measured ice surface velocities. The simulations indicate cold ice at higher elevations, while temperate ice at lower elevations is consistent with the observations.
    Keywords: ELEVATION; Ice-flow direction; King_George_Island; King George Island, Antarctic Peninsula; LATITUDE; LONGITUDE; Priority Programme 1158 Antarctic Research with Comparable Investigations in Arctic Sea Ice Areas; SPP1158; UTM Easting, Universal Transverse Mercator; UTM Northing, Universal Transverse Mercator; UTM Zone, Universal Transverse Mercator; Velocity magnitude
    Type: Dataset
    Format: text/tab-separated-values, 610 data points
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    DATA PANGAEA
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