scholarly journals Reaction Of The Heat Regime Of Antarctic Ice Sheet Inland Regions On Long-Term Changes Of Climate

1990 ◽  
Vol 14 ◽  
pp. 329-329
Author(s):  
Vitaly Barbash
Keyword(s):  
Temperature Field ◽  
Ice Sheet ◽  
Heat Regime ◽  
Antarctic Ice Sheet ◽  
Field Surveys ◽  
Climatic Variations ◽  
Long Term Changes ◽  
The Antarctic ◽  
Isotope Analyses

A nonstationary mathematical model of thermics and dynamics of the Antarctic ice sheet has been developed, taking into consideration the influence of long-term changes of climate.The influence of climatic variations during the last 100 000 years on the temperature field within the ice sheet has been analysed. Information about climatic changes is based on paleographic data and isotope analyses of ice samples from bore holes at Vostok and Byrd stations.The input data used include results from field surveys of accumulation, temperatures of upper surface, relief of the base and thickness of the ice sheet along the flowlines in the western and eastern parts of the ice sheet, as well as experimental data on ice rheology.The computations show that traces of the climatic minimum that took place about 18 000 years ago are found in the temperature field of the Antarctic ice sheet.The model developed has proved that warming of climate due to the “greenhouse effect” leads to significant changes in the thermal regime in the upper parts of the ice sheet, but will not lead to conditions threatening bottom layers.

scholarly journals Reaction Of The Heat Regime Of Antarctic Ice Sheet Inland Regions On Long-Term Changes Of Climate

1990 ◽  
Vol 14 ◽  
pp. 329
Author(s):  
Vitaly Barbash
Keyword(s):  
Temperature Field ◽  
Ice Sheet ◽  
Heat Regime ◽  
Antarctic Ice Sheet ◽  
Field Surveys ◽  
Climatic Variations ◽  
Long Term Changes ◽  
The Antarctic ◽  
Isotope Analyses

A nonstationary mathematical model of thermics and dynamics of the Antarctic ice sheet has been developed, taking into consideration the influence of long-term changes of climate. The influence of climatic variations during the last 100 000 years on the temperature field within the ice sheet has been analysed. Information about climatic changes is based on paleographic data and isotope analyses of ice samples from bore holes at Vostok and Byrd stations. The input data used include results from field surveys of accumulation, temperatures of upper surface, relief of the base and thickness of the ice sheet along the flowlines in the western and eastern parts of the ice sheet, as well as experimental data on ice rheology. The computations show that traces of the climatic minimum that took place about 18 000 years ago are found in the temperature field of the Antarctic ice sheet. The model developed has proved that warming of climate due to the “greenhouse effect” leads to significant changes in the thermal regime in the upper parts of the ice sheet, but will not lead to conditions threatening bottom layers.

scholarly journals Are longitudinal ice-surface structures on the Antarctic Ice Sheet indicators of long-term ice-flow configuration?

2014 ◽  
Vol 2 (2) ◽  
pp. 911-933 ◽  
Author(s):  
N. F. Glasser ◽  
S. J. A. Jennings ◽  
M. J. Hambrey ◽  
B. Hubbard
Keyword(s):  
Flow Line ◽  
Ice Sheet ◽  
Surface Structures ◽  
Surface Velocity ◽  
Ice Flow ◽  
Antarctic Ice Sheet ◽  
Ice Surface ◽  
Ice Stream ◽  
The Antarctic

Abstract. Continent-wide mapping of longitudinal ice-surface structures on the Antarctic Ice Sheet reveals that they originate in the interior of the ice sheet and are arranged in arborescent networks fed by multiple tributaries. Longitudinal ice-surface structures can be traced continuously down-ice for distances of up to 1200 km. They are co-located with fast-flowing glaciers and ice streams that are dominated by basal sliding rates above tens of m yr-1 and are strongly guided by subglacial topography. Longitudinal ice-surface structures dominate regions of converging flow, where ice flow is subject to non-coaxial strain and simple shear. Associating these structures with the AIS' surface velocity field reveals (i) ice residence times of ~ 2500 to 18 500 years, and (ii) undeformed flow-line sets for all major flow units analysed except the Kamb Ice Stream and the Institute and Möller Ice Stream areas. Although it is unclear how long it takes for these features to form and decay, we infer that the major ice-flow and ice-velocity configuration of the ice sheet may have remained largely unchanged for several thousand years, and possibly even since the end of the last glacial cycle. This conclusion has implications for our understanding of the long-term landscape evolution of Antarctica, including large-scale patterns of glacial erosion and deposition.

scholarly journals Antarctic Palaeotopography

2021 ◽  
pp. M56-2020-7
Author(s):  
Guy J. G. Paxman
Keyword(s):  
Ice Sheet ◽  
Future Research ◽  
Dynamic Topography ◽  
Antarctic Ice Sheet ◽  
Isostatic Adjustment ◽  
Subglacial Topography ◽  
Mantle Processes ◽  
Ice Sheet Dynamics ◽  
The Antarctic

AbstractThe development of a robust understanding of the response of the Antarctic Ice Sheet to present and projected future climatic change is a matter of key global societal importance. Numerical ice sheet models that simulate future ice sheet behaviour are typically evaluated with recourse to how well they reproduce past ice sheet behaviour, which is constrained by the geological record. However, subglacial topography, a key boundary condition in ice sheet models, has evolved significantly throughout Antarctica's glacial history. Since mantle processes play a fundamental role in the generation and modification of topography over geological timescales, an understanding of the interactions between the Antarctic mantle and palaeotopography is crucial for developing more accurate simulations of past ice sheet dynamics. This chapter provides a review of the influence of the Antarctic mantle on the long-term evolution of the subglacial landscape, through processes including structural inheritance, flexural isostatic adjustment, lithospheric cooling and thermal subsidence, volcanism and dynamic topography. The uncertainties associated with reconstructing these processes through time are discussed, as are important directions for future research and the implications of the evolving subglacial topography for the response of the Antarctic Ice Sheet to climatic and oceanographic change.

scholarly journals Modelling the long-term response of the Antarctic ice sheet to global warming

1998 ◽  
Vol 27 ◽  
pp. 161-168 ◽  
Author(s):  
Roland C. Warner ◽  
W.Κ. Budd
Keyword(s):  
Global Warming ◽  
Mass Loss ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
Basal Melting ◽  
The Antarctic ◽  
Term Response

The primary effects of global warming on the Antarctic ice sheet can involve increases in surface melt for limited areas at lower elevations, increases in net accumulation, and increased basal melting under floating ice. For moderate global wanning, resulting in ocean temperature increases of a few °C, the large- increase in basal melting can become the dominant factor in the long-term response of the ice sheet. The results from ice-sheet modelling show that the increased basal melt rates lead to a reduction of the ice shelves, increased strain rates and flow at the grounding lines, then thinning and floating of the marine ice sheets, with consequential further basal melting. The mass loss from basal melting is counteracted to some extent by the increased accumulation, but in the long term the area of ice cover decreases, particularly in West Antarctica, and the mass loss can dominate. The ice-sheet ice-shelf model of Budd and others (1994) with 20 km resolution has been modified and used to carry out a number of sensitivity studies of the long-term response of the ice sheet to prescribed amounts of global warming. The changes in the ice sheet are computed out to near-equilibrium, but most of the changes take place with in the first lew thousand years. For a global mean temperature increase of 3°C with an ice-shelf basal melt rate of 5 m a−1 the ice shelves disappear with in the first few hundred years, and the marine-based parts of the ice sheet thin and retreat. By 2000 years the West Antarctic region is reduced to a number of small, isolated ice caps based on the bedrock regions which are near or above sea level. This allows the warmer surface ocean water to circulate through the archipelago in summer, causing a large change to the local climate of the region.

scholarly journals The Heat Regime of the Central Parts of the Antarctic Ice Sheet with Changing Climate (Abstract only)

1982 ◽  
Vol 3 ◽  
pp. 343
Author(s):  
V.R. Barbash ◽  
I.A. Zotikov
Keyword(s):  
Numerical Modelling ◽  
Surface Temperature ◽  
Greenhouse Effect ◽  
Ice Sheet ◽  
Heat Regime ◽  
Antarctic Ice Sheet ◽  
Temperature Changes ◽  
Dissipation Term ◽  
Vostok Station ◽  
The Antarctic

The heat regime and dynamics of the Antarctic ice sheet are studied using numerical modelling for two flow lines, one of which passes Vostok station and the other Byrd station. A two-dimensional non-steady heat-transfer equation with an energy dissipation term was used. The study consists of two parts. The first is a study of velocity and temperature distributions within the glacier under steady-state conditions. The second study was performed assuming surface temperature changes intended to model palaeoclimatic changes for the last 100 ka and also to model future climate changes due to a possible "greenhouse" effect. Computer numerical modelling shows that the Antarctic ice sheet retains a record of the climatic temperature minimum 18 ka BP. Numerical modelling of the greenhouse effect assumes a temperature increasing by 10 deg within the next 100 a; its influence increases after this even if the surface temperature then remains the same for the next 20 ka. It is shown that for the next 1 ka the temperature wave will penetrate only a thin surface layer of the ice. Even in 20 ka the bottom temperature of the ice sheet will still be unchanged. Small increases of ice velocity can produce ice-sheet thinning of the order of 10 mm a−1.

scholarly journals Modelling present-day basal melt rates for Antarctic ice shelves using a parametrization of buoyant meltwater plumes

2018 ◽  
Vol 12 (1) ◽  
pp. 49-70 ◽  
Author(s):  
Werner M. J. Lazeroms ◽  
Adrian Jenkins ◽  
G. Hilmar Gudmundsson ◽  
Roderik S. W. van de Wal
Keyword(s):  
Temperature Field ◽  
Ice Sheet ◽  
Detailed Knowledge ◽  
Ocean Temperature ◽  
Ice Shelf ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
Grounding Line ◽  
The Antarctic ◽  
Line Depth

Abstract. Basal melting below ice shelves is a major factor in mass loss from the Antarctic Ice Sheet, which can contribute significantly to possible future sea-level rise. Therefore, it is important to have an adequate description of the basal melt rates for use in ice-dynamical models. Most current ice models use rather simple parametrizations based on the local balance of heat between ice and ocean. In this work, however, we use a recently derived parametrization of the melt rates based on a buoyant meltwater plume travelling upward beneath an ice shelf. This plume parametrization combines a non-linear ocean temperature sensitivity with an inherent geometry dependence, which is mainly described by the grounding-line depth and the local slope of the ice-shelf base. For the first time, this type of parametrization is evaluated on a two-dimensional grid covering the entire Antarctic continent. In order to apply the essentially one-dimensional parametrization to realistic ice-shelf geometries, we present an algorithm that determines effective values for the grounding-line depth and basal slope in any point beneath an ice shelf. Furthermore, since detailed knowledge of temperatures and circulation patterns in the ice-shelf cavities is sparse or absent, we construct an effective ocean temperature field from observational data with the purpose of matching (area-averaged) melt rates from the model with observed present-day melt rates. Our results qualitatively replicate large-scale observed features in basal melt rates around Antarctica, not only in terms of average values, but also in terms of the spatial pattern, with high melt rates typically occurring near the grounding line. The plume parametrization and the effective temperature field presented here are therefore promising tools for future simulations of the Antarctic Ice Sheet requiring a more realistic oceanic forcing.

Developing an emulator to calculate present temperature field in the Antarctic Ice Sheet

2021 ◽  
Author(s):  
Catherine Ritz ◽  
Christophe Dumas ◽  
Marion Leduc-Leballeur ◽  
Giovanni Macelloni ◽  
Ghislain Picard ◽  
...  
Keyword(s):  
Temperature Field ◽  
Ice Sheet ◽  
Surface Velocity ◽  
Computational Time ◽  
Ice Thickness ◽  
Ice Flow ◽  
Antarctic Ice Sheet ◽  
Computationally Expensive ◽  
The Antarctic ◽  
Geothermal Flux

<p><span>Ice temperature within the ice is a crucial characteristic to understand the Antarctic ice sheet evolution because temperature is coupled to ice flow. Since temperature is only measured at few locations in deep boreholes, we only rely on numerical modelling to assess ice sheet-wide temperature. However, the design of such models leads to a number of challenges. One important difficulty is that the temperature field strongly depends on the geothermal flux which is still poorly known (see White paper by Burton-Johnson and others,2020 </span><span></span><span>). Another point is that up to now there is no fully suitable model, especially for inverse approaches: i</span><span>)</span><span> analytical solutions are only valid in slowly flowing regions; ii</span><span>)</span><span> models solving only the heat equation by prescribing geometry and ice flow do not take into account the past changes in ice thickness and ice flow and </span><span>do not couple </span><span>ice flow and temperature. Conversely, 3D thermomechanical models that simulate the evolution of the ice sheet take into account all the relevant processes but they are too computationally expensive to be used in inverse approaches. Moreover, they do not provide a perfect fit between observed and simulated geometry </span><span>(ice thickness, surface elevation) </span><span>for the present-day ice sheets </span><span>and this affects the simulated temperature field</span><span>.</span></p><p><span>GRISLI (Quiquet et al. 2018), belongs to this family of thermomechanically coupled ice sheet models An emulator, based on deep neural network (DNN), has been developed in order to speed-up the simulation of present-day ice temperature. We use GRISLI outputs that come from 4 simulations, each covers 900000 years (8 glacial-interglacial cycles) to get rid of the initial configuration influence. The simulations differ by the geothermal flux map used as boundary condition. Finally a database is built where each ice column for each simulation is a sample used to train the DNN. For each sample, the input layer (precursor) is a vector of the present-day characteristics: ice thickness, surface temperature, geothermal flux, accumulation rate, surface velocity and surface slope. The predicted output (output layer) is the vertical profile of temperature. In the training, the weights of the network are optimized by comparison with the GRISLI temperature. </span></p><p><span>The first results are very encouraging with a RMSE of ~ 0.6 °C (calculated from the difference between the emulated temperatures and GRISLI temperatures over all the samples and all the depths). Once trained, the computational time of GRISLI-DNN for generating temperature field of whole Antarctica (16000 columns) is about 20 s.</span></p><p><span>The first application (in the framework of the ESA project 4D-Antarctica, see Leduc-Leballeur<span> presentation in this session</span>) will be to use this emulator associated with SMOS satellite observations to infer the 3D temperature field and improve our knowledge of geothermal flux. Indeed, it has been shown that SMOS data, coupled with glaciological and electromagnetic models, give an indication of temperature in the upper 1000 m of the ice sheet. Our emulator could also be used for initialization of computationally expensive ice sheet models.</span></p>

An assessment of basal melting parameterisations for Antarctic ice shelves

2021 ◽  
Author(s):  
Clara Burgard ◽  
Nicolas Jourdain
Keyword(s):  
Climate Model ◽  
Ice Sheet ◽  
Coupled Model ◽  
Ice Shelf ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
Global Sea Level ◽  
Basal Melting ◽  
The Antarctic

<p>Ocean-induced melting at the base of ice shelves is one of the main drivers of the currently observed mass loss of the Antarctic Ice Sheet. A good understanding of the interaction between ice and ocean at the base of the ice shelves is therefore crucial to understand and project the Antarctic contribution to global sea-level rise. </p><p>Due to the high difficulty to monitor these regions, our understanding of the processes at work beneath ice shelves is limited. Still, several parameterisations of varying complexity have been developed in past decades to describe the ocean-induced sub-shelf melting. These parameterisations can be implemented into standalone ice-sheet models, for example when conducting long-term projections forced with climate model output.</p><p>An assessment of the performance of these parameterisations was conducted in an idealised setup (Favier et al, 2019). However, the application of the better-performing parameterisations in a more realistic setup (e.g. Jourdain et al., 2020) has shown that individual adjustments and corrections are needed for each ice shelf.</p><p>In this study, we revisit the assessment of the parameterisations, this time in a more realistic setup than previous studies. To do so, we apply the different parameterisations on several ice shelves around Antarctica and compare the resulting melt rates to satellite and oceanographic estimates. Based on this comparison, we will refine the parameters and propose an approach to reduce uncertainties in long-term sub-shelf melting projections.</p><p><em>References</em><br><em>- Favier, L., Jourdain, N. C., Jenkins, A., Merino, N., Durand, G., Gagliardini, O., Gillet-Chaulet, F., and Mathiot, P.: Assessment of sub-shelf melting parameterisations using the ocean–ice-sheet coupled model NEMO(v3.6)–Elmer/Ice(v8.3) , Geosci. Model Dev., 12, 2255–2283, https://doi.org/10.5194/gmd-12-2255-2019, 2019. </em><br><em>- Jourdain, N. C., Asay-Davis, X., Hattermann, T., Straneo, F., Seroussi, H., Little, C. M., and Nowicki, S.: A protocol for calculating basal melt rates in the ISMIP6 Antarctic ice sheet projections, The Cryosphere, 14, 3111–3134, https://doi.org/10.5194/tc-14-3111-2020, 2020. </em></p>

scholarly journals The GRISLI ice sheet model (version 2.0): calibration and validation for multi-millennial changes of the Antarctic ice sheet

2018 ◽  
Author(s):  
Aurélien Quiquet ◽  
Christophe Dumas ◽  
Catherine Ritz ◽  
Vincent Peyaud ◽  
Didier M. Roche
Keyword(s):  
Ice Sheet ◽  
Climate Forcing ◽  
Antarctic Ice Sheet ◽  
Ice Volume ◽  
Grounding Line ◽  
Version 2.0 ◽  
The Antarctic ◽  
Climate Proxies ◽  
Ice Model

Abstract. In this paper we present the GRISLI (Grenoble Ice Sheet and Land Ice) model in its newest revision (version 2.0). Whilst GRISLI is applicable to any given geometry, we focus here on the Antarctic ice sheet because it highlights the importance of grounding line dynamics. Important improvements have been implemented since its original version (Ritz et al., 2001) including notably an explicit flux computation at the grounding line based on the analytical formulations of Schoof (2007) and Tsai et al. (2015) and a basal hydrology model. A calibration of the mechanical parameters of the model based on an ensemble of 150 members sampled with a Latin Hypercube method is used. The ensemble members performance is assessed relative to the deviation from present-day observed Antarctic ice thickness. The model being designed for multi-millenial long- term integrations, we also present glacial-interglacial ice sheet changes throughout the last 400 kyr using the best ensemble members. To achieve this goal, we construct a simple climatic perturbation of present-day climate forcing fields based on two climate proxies, both atmospheric and oceanic. The model is able to reproduce expected grounding line advances during glacials and subsequent retreats during terminations with reasonable glacial-interglacial ice volume changes.

scholarly journals The GRISLI ice sheet model (version 2.0): calibration and validation for multi-millennial changes of the Antarctic ice sheet

2018 ◽  
Vol 11 (12) ◽  
pp. 5003-5025 ◽  
Author(s):  
Aurélien Quiquet ◽  
Christophe Dumas ◽  
Catherine Ritz ◽  
Vincent Peyaud ◽  
Didier M. Roche
Keyword(s):  
Ice Sheet ◽  
Climate Forcing ◽  
Method Performance ◽  
Antarctic Ice Sheet ◽  
Grounding Line ◽  
Version 2.0 ◽  
Glacial Periods ◽  
The Antarctic ◽  
Climate Proxies

Abstract. In this paper, we present the GRISLI (Grenoble ice sheet and land ice) model in its newest revision (version 2.0). Whilst GRISLI is applicable to any given ice sheet, we focus here on the Antarctic ice sheet because it highlights the importance of grounding line dynamics. Important improvements have been implemented in the model since its original version (Ritz et al., 2001). Notably, GRISLI now includes a basal hydrology model and an explicit flux computation at the grounding line based on the analytical formulations of Schoof (2007) or Tsai et al. (2015). We perform a full calibration of the model based on an ensemble of 300 simulations sampling mechanical parameter space using a Latin hypercube method. Performance of individual members is assessed relative to the deviation from present-day observed Antarctic ice thickness. To assess the ability of the model to simulate grounding line migration, we also present glacial–interglacial ice sheet changes throughout the last 400 kyr using the best ensemble members taking advantage of the capacity of the model to perform multi-millennial long-term integrations. To achieve this goal, we construct a simple climatic perturbation of present-day climate forcing fields based on two climate proxies: atmospheric and oceanic. The model is able to reproduce expected grounding line advances during glacial periods and subsequent retreats during terminations with reasonable glacial–interglacial ice volume changes.

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