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  • 2020-2024  (11)
  • 2015-2019  (37)
  • 1
    Publikationsdatum: 2023-11-13
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: Bundesministerium für Bildung und Forschung (Federal Ministry of Education and Research) https://doi.org/10.13039/501100002347
    Beschreibung: European Union’s Horizon 2020 Research and Innovation Programme
    Beschreibung: https://doi.org/10.1594/PANGAEA.928940
    Beschreibung: https://nsidc.org/data/IDBMG4
    Beschreibung: https://gitlab.awi.de/jchristm/viscoelastic-79ng-greenland
    Beschreibung: https://doi.org/10.5281/zenodo.5507115
    Beschreibung: https://doi.org/10.5281/zenodo.5506953
    Schlagwort(e): ddc:551.31 ; Climate change ; Cryospheric science ; Hydrology
    Sprache: Englisch
    Materialart: doc-type:article
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 2
    Publikationsdatum: 2023-03-16
    Schlagwort(e): Antarctica; AWI_Glac; Glaciology @ AWI
    Materialart: Dataset
    Format: application/x-netcdf, 12.8 MBytes
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
    Publikationsdatum: 2023-03-16
    Schlagwort(e): Antarctica; AWI_Glac; DATE/TIME; Glaciology @ AWI; Ice thickness, glacier; LATITUDE; LONGITUDE
    Materialart: Dataset
    Format: text/tab-separated-values, 104080 data points
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 4
    facet.materialart.
    Unbekannt
    PANGAEA
    In:  Supplement to: Humbert, Angelika; Steinhage, Daniel; Helm, Veit; Beyer, Sebastian; Kleiner, Thomas (2018): Missing Evidence of Widespread Subglacial Lakes at Recovery Glacier, Antarctica. Journal of Geophysical Research-Earth Surface, 123(11), 2802-2826, https://doi.org/10.1029/2017JF004591
    Publikationsdatum: 2023-03-16
    Beschreibung: Recovery Glacier reaches far into the East Antarctic Ice Sheet. Recent projections point out that its dynamic behaviour has a considerable impact on future Antarctic ice loss (Golledge et al. 2017). Subglacial lakes are thought to play a major role in the initiation of the rapid ice flow (Bell et al. 2007). Satellite altimetry observations have even suggested several actively filling and draining subglacial lakes beneath the main trunk (Smith et al. 2009). We present new data of the geometry of this glacier and investigate its basal properties employing radio-echo sounding. Using ice-sheet modelling, we were able to constrain estimates of radar absorption in the ice, but uncertainties remain large. The magnitude of the basal reflection coefficient is thus still poorly known. However, its spatial variability, in conjunction with additional indicators, can be used to infer the presence of subglacial water. We find no clear evidence of water at most of the previously proposed lake sites. Especially locations where altimetry detected active lakes, do not exhibit lake characteristics in RES. We argue that lakes far upstream the main trunk are not triggering enhanced ice flow, which is also supported by modeled subglacial hydrology.
    Schlagwort(e): Antarctica; AWI_Glac; Glaciology @ AWI
    Materialart: Dataset
    Format: application/zip, 2 datasets
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  • 5
    facet.materialart.
    Unbekannt
    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
    Publikationsdatum: 2023-01-13
    Beschreibung: 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.
    Schlagwort(e): Jakobshavn_Isbræ_drainage_basin; West Greenland
    Materialart: Dataset
    Format: application/zip, 469.2 MBytes
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  • 6
    facet.materialart.
    Unbekannt
    PANGAEA
    In:  Supplement to: Bons, Paul D; Kleiner, Thomas; Llorens, Maria-Gema; Prior, David J; Sachau, Till; Weikusat, Ilka; Jansen, Daniela (2018): Greenland Ice Sheet: Higher Nonlinearity of Ice Flow Significantly Reduces Estimated Basal Motion. Geophysical Research Letters, 45(13), 6542-6548, https://doi.org/10.1029/2018GL078356
    Publikationsdatum: 2023-02-06
    Beschreibung: In times of warming in polar regions, the prediction of ice sheet discharge is of utmost importance to society, because of its impact on sea level rise. In simulations the flow rate of ice is usually implemented as proportional to the differential stress to the power of the exponent n=3. This exponent influences the softness of the modeled ice, as higher values would produce faster flow under equal stress. We show that the stress exponent, which best fits the observed state of the Greenland Ice Sheet, equals n=4, Our results, which are not dependent on a possible basal sliding component of flow, indicate that most of the interior northern ice sheet is currently frozen to bedrock, except for the large ice streams and marginal ice.
    Schlagwort(e): File content; File format; File name; File size; MULT; Multiple investigations; Northern_Greenland_Ice_Sheet; Uniform resource locator/link to file
    Materialart: Dataset
    Format: text/tab-separated-values, 75 data points
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 7
    Publikationsdatum: 2024-04-20
    Beschreibung: We provide a data set to investigate the subglacial properties of the East Antarctic Ice Sheet by statistically analysing the roughness of the bed topography, inferred from radio-echo sounding measurements. We analyse two sets of roughness parameters, one derived in the spatial and the other in the spectral domain, with two roughness parameters each. This enables us to compare the suitability of the four roughness parameters to classify the subglacial landscapes below the ice sheet.
    Schlagwort(e): Antarctica; bedrock; Binary Object; Binary Object (File Size); East_Antarctica; MULT; Multiple investigations; Radar Data; radio-echo sounding
    Materialart: Dataset
    Format: text/tab-separated-values, 14 data points
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 8
    Publikationsdatum: 2021-01-08
    Beschreibung: Ice sheet numerical modeling is an important tool to estimate the dynamic contribution of the Antarctic ice sheet to sea level rise over the coming centuries. The influence of initial conditions on ice sheet model simulations, however, is still unclear. To better understand this influence, an initial state intercomparison exercise (initMIP) has been developed to compare, evaluate, and improve initialization procedures and estimate their impact on century-scale simulations. initMIP is the first set of experiments of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), which is the primary Coupled Model Intercomparison Project Phase 6 (CMIP6) activity focusing on the Greenland and Antarctic ice sheets. Following initMIP-Greenland, initMIP-Antarctica has been designed to explore uncertainties associated with model initialization and spin-up and to evaluate the impact of changes in external forcings. Starting from the state of the Antarctic ice sheet at the end of the initialization procedure, three forward experiments are each run for 100 years: a control run, a run with a surface mass balance anomaly, and a run with a basal melting anomaly beneath floating ice. This study presents the results of initMIP-Antarctica from 25 simulations performed by 16 international modeling groups. The submitted results use different initial conditions and initialization methods, as well as ice flow model parameters and reference external forcings. We find a good agreement among model responses to the surface mass balance anomaly but large variations in responses to the basal melting anomaly. These variations can be attributed to differences in the extent of ice shelves and their upstream tributaries, the numerical treatment of grounding line, and the initial ocean conditions applied, suggesting that ongoing efforts to better represent ice shelves in continental-scale models should continue.
    Materialart: Article , PeerReviewed
    Format: text
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  • 9
    Publikationsdatum: 2018-09-03
    Beschreibung: 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.
    Materialart: Article , NonPeerReviewed
    Format: text
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  • 10
    Publikationsdatum: 2021-01-08
    Beschreibung: The international endeavour to retrieve a continuous ice core, which spans the middle Pleistocene climate transition ca. 1.2–0.9 Myr ago, encompasses a multitude of field and model-based pre-site surveys. We expand on the current efforts to locate a suitable drilling site for the oldest Antarctic ice core by means of 3-D continental ice-sheet modelling. To this end, we present an ensemble of ice-sheet simulations spanning the last 2 Myr, employing transient boundary conditions derived from climate modelling and climate proxy records. We discuss the imprint of changing climate conditions, sea level and geothermal heat flux on the ice thickness, and basal conditions around previously identified sites with continuous records of old ice. Our modelling results show a range of configurational ice-sheet changes across the middle Pleistocene transition, suggesting a potential shift of the West Antarctic Ice Sheet to a marine-based configuration. Despite the middle Pleistocene climate reorganisation and associated ice-dynamic changes, we identify several regions conducive to conditions maintaining 1.5 Myr (million years) old ice, particularly around Dome Fuji, Dome C and Ridge B, which is in agreement with previous studies. This finding strengthens the notion that continuous records with such old ice do exist in previously identified regions, while we are also providing a dynamic continental ice-sheet context.
    Materialart: Article , PeerReviewed
    Format: text
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