scholarly journals Modelling water flow under glaciers and ice sheets

2015 ◽  
Vol 471 (2176) ◽  
pp. 20140907 ◽  
Author(s):  
Gwenn E. Flowers
Keyword(s):  
Rapid Development ◽  
Ice Sheets ◽  
Coupled System ◽  
Ice Streams ◽  
Widespread Application ◽  
Ice Flow ◽  
Strict Adherence ◽  
Mountain Glaciers ◽  
Subglacial Environment ◽  
Subglacial Drainage

Recent observations of dynamic water systems beneath the Greenland and Antarctic ice sheets have sparked renewed interest in modelling subglacial drainage. The foundations of today's models were laid decades ago, inspired by measurements from mountain glaciers, discovery of the modern ice streams and the study of landscapes evacuated by former ice sheets. Models have progressed from strict adherence to the principles of groundwater flow, to the incorporation of flow ‘elements’ specific to the subglacial environment, to sophisticated two-dimensional representations of interacting distributed and channelized drainage. Although presently in a state of rapid development, subglacial drainage models, when coupled to models of ice flow, are now able to reproduce many of the canonical phenomena that characterize this coupled system. Model calibration remains generally out of reach, whereas widespread application of these models to large problems and real geometries awaits the next level of development.

scholarly journals Deep learning speeds up ice flow modelling by several orders of magnitude

2021 ◽  
pp. 1-14
Author(s):  
Guillaume Jouvet ◽  
Guillaume Cordonnier ◽  
Byungsoo Kim ◽  
Martin Lüthi ◽  
Andreas Vieli ◽  
...  
Keyword(s):  
High Spatial Resolution ◽  
State Of The Art ◽  
Ice Sheets ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Flow Models ◽  
Mountain Glaciers ◽  
Central Processing ◽  
Model Component ◽  
User Friendly

Abstract This paper introduces the Instructed Glacier Model (IGM) – a model that simulates ice dynamics, mass balance and its coupling to predict the evolution of glaciers, icefields or ice sheets. The novelty of IGM is that it models the ice flow by a Convolutional Neural Network, which is trained from data generated with hybrid SIA + SSA or Stokes ice flow models. By doing so, the most computationally demanding model component is substituted by a cheap emulator. Once trained with representative data, we demonstrate that IGM permits to model mountain glaciers up to 1000 × faster than Stokes ones on Central Processing Units (CPU) with fidelity levels above 90% in terms of ice flow solutions leading to nearly identical transient thickness evolution. Switching to the GPU often permits additional significant speed-ups, especially when emulating Stokes dynamics or/and modelling at high spatial resolution. IGM is an open-source Python code which deals with two-dimensional (2-D) gridded input and output data. Together with a companion library of trained ice flow emulators, IGM permits user-friendly, highly efficient and mechanically state-of-the-art glacier and icefields simulations.

scholarly journals Flow-switching and water piracy between Rutford Ice Stream and Carlson Inlet, West Antarctica

2008 ◽  
Vol 54 (184) ◽  
pp. 41-48 ◽  
Author(s):  
David G. Vaughan ◽  
Hugh F.J. Corr ◽  
Andy M. Smith ◽  
Hamish D. Pritchard ◽  
Andrew Shepherd
Keyword(s):  
Indirect Evidence ◽  
West Antarctica ◽  
Ice Streams ◽  
Ice Flow ◽  
Stream Flows ◽  
Current State ◽  
Ice Stream ◽  
State Of Water ◽  
Almost All ◽  
Subglacial Drainage

AbstractRutford Ice Stream and Carlson Inlet are neighbouring glaciers in West Antarctica. Rutford Ice Stream flows at speeds greater than 350 m a−1, whereas Carlson Inlet, which has some similar dimensions and supports a similar driving stress, flows 10–50 times slower. We discuss a range of observations concerning Carlson Inlet, and conclude that there is good indirect evidence that it is a relict ice stream, which ceased streaming more than 240 years BP, but sufficiently recently that its surface morphology, basal water content and basal morphology still retain characteristics produced by streaming. An analysis of expected subglacial drainage pathways indicates that Carlson Inlet is not streaming because it is currently starved of subglacial water, which is currently directed beneath Rutford Ice Stream. This current state of water piracy by Rutford Ice Stream is, however, sensitive to minor thickness changes on the ice streams; a ∼120 m (<4%) thickening of Rutford Ice Stream would divert almost all the subglacial water in the system towards Carlson Inlet and could reactivate its flow. The result highlights the importance of subglacial drainage in controlling ice-stream evolution and the requirement for ice-sheet models to couple ice flow with subglacial drainage.

scholarly journals Of isbræ and ice streams

2003 ◽  
Vol 36 ◽  
pp. 66-72 ◽  
Author(s):  
Martin Truffer ◽  
Keith A. Echelmeyer
Keyword(s):  
Ice Sheet ◽  
Shear Zones ◽  
West Antarctica ◽  
Ice Streams ◽  
Ice Flow ◽  
Bed Topography ◽  
Ice Stream ◽  
Fast Ice ◽  
Fast Flow ◽  
End Members

AbstractFast-flowing ice streams and outlet glaciers provide the major avenues for ice flow from past and present ice sheets. These ice streams move faster than the surrounding ice sheet by a factor of 100 or more. Several mechanisms for fast ice-stream flow have been identified, leading to a spectrum of different ice-stream types. In this paper we discuss the two end members of this spectrum, which we term the “ice-stream” type (represented by the Siple Coast ice streams in West Antarctica) and the “isbræ” type (represented by Jakobshavn Isbræ in Greenland). The typical ice stream is wide, relatively shallow (∼1000 m), has a low surface slope and driving stress (∼10 kPa), and ice-stream location is not strongly controlled by bed topography. Fast flow is possible because the ice stream has a slippery bed, possibly underlain by weak, actively deforming sediments. The marginal shear zones are narrow and support most of the driving stress, and the ice deforms almost exclusively by transverse shear. The margins seem to be inherently unstable; they migrate, and there are plausible mechanisms for such ice streams to shut down. The isbræ type of ice stream is characterized by very high driving stresses, often exceeding 200 kPa. They flow through deep bedrock channels that are significantly deeper than the surrounding ice, and have steep surface slopes. Ice deformation includes vertical as well as lateral shear, and basal motion need not contribute significantly to the overall motion. The marginal shear zone stend to be wide relative to the isbræ width, and the location of isbræ and its margins is strongly controlled by bedrock topography. They are stable features, and can only shut down if the high ice flux cannot be supplied from the adjacent ice sheet. Isbræs occur in Greenland and East Antarctica, and possibly parts of Pine Island and Thwaites Glaciers, West Antarctica. In this paper, we compare and contrast the two types of ice streams, addressing questions such as ice deformation, basal motion, subglacial hydrology, seasonality of ice flow, and stability of the ice streams.

scholarly journals Dynamical processes involved in the retreat of marine ice sheets

2001 ◽  
Vol 47 (157) ◽  
pp. 271-282 ◽  
Author(s):  
Richard C.A. Hindmarsh ◽  
E. Le Meur
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Streams ◽  
Antarctic Ice Sheet ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
Grounding Line ◽  
Neutral Equilibrium ◽  
Generally True

AbstractMarine ice sheets with mechanics described by the shallow-ice approximation by definition do not couple mechanically with the shelf. Such ice sheets are known to have neutral equilibria. We consider the implications of this for their dynamics and in particular for mechanisms which promote marine ice-sheet retreat. The removal of ice-shelf buttressing leading to enhanced flow in grounded ice is discounted as a significant influence on mechanical grounds. Sea-level rise leading to reduced effective pressures under ice streams is shown to be a feasible mechanism for producing postglacial West Antarctic ice-sheet retreat but is inconsistent with borehole evidence. Warming thins the ice sheet by reducing the average viscosity but does not lead to grounding-line retreat. Internal oscillations either specified or generated via a MacAyeal–Payne thermal mechanism promote migration. This is a noise-induced drift phenomenon stemming from the neutral equilibrium property of marine ice sheets. This migration occurs at quite slow rates, but these are sufficiently large to have possibly played a role in the dynamics of the West Antarctic ice sheet after the glacial maximum. Numerical experiments suggest that it is generally true that while significant changes in thickness can be caused by spatially uniform changes, spatial variability coupled with dynamical variability is needed to cause margin movement.

scholarly journals Thermomechanical modelling of the Scandinavian ice sheet: implications for ice-stream formation

1999 ◽  
Vol 28 ◽  
pp. 83-89 ◽  
Author(s):  
A. J. Payne ◽  
D.J. Baldwin
Keyword(s):  
Three Dimensional ◽  
Ice Sheet ◽  
Ice Streams ◽  
Ice Flow ◽  
Low Viscosity ◽  
Ice Stream ◽  
Scandinavian Ice Sheet ◽  
The Baltic ◽  
Stream Formation ◽  
Initial Results

AbstractThis work attempts to explain the fan-like landform assemblages observed in satellite images of the area covered by the former Scandinavian ice sheet (SIS). These assemblages have been interpreted as evidence of large ice streams within the SIS. If this interpretation is correct, then it calls into doubt current theories on the formation of ice streams. These theories regard soft sediment and topographic troughs as being the key determinants of ice-stream location. Neither can be used to explain the existence of ice streams on the flat, hard-rock area of the Baltic Shield. Initial results from a three-dimensional, thermomechanical ice-sheet model indicate that interactions between ice flow, form and temperature can create patterns similar to those mentioned above. The model uses a realistic, 20 km resolution gridded topography and a simple parameterization of accumulation and ablation. It produces patterns of maximum ice-sheet extent, which are similar to those reconstructed from the area’s glacial geomorphology. Flow in the maximum, equilibrium ice sheet is dominated by wedges of warm, low-viscosity, fast-flowing ice. These are separated by areas of cold, slow-flowing ice. This patterning appears to develop spontaneously as the modelled ice sheet grows.

Ribbed bedforms, markers of palaeo-ice stream margins, basal meltwater drainage and ice flow dynamic

2021 ◽  
Author(s):  
Jean Vérité ◽  
Édouard Ravier ◽  
Olivier Bourgeois ◽  
Stéphane Pochat ◽  
Thomas Lelandais ◽  
...  
Keyword(s):  
Flow Direction ◽  
Local Stress ◽  
Sediment Surface ◽  
Shear Stresses ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Stream ◽  
Physical Experiments ◽  
Stream Beds ◽  
Ice Water

&lt;p&gt;Over the three last decades, great efforts have been undertaken by the glaciological community to characterize the behaviour of ice streams and better constrain the dynamics of ice sheets. Studies of modern ice stream beds reveal crucial information on ice-meltwater-till-bedrock interactions, but are restricted to punctual observations limiting the understanding of ice stream dynamics as a whole. Consequently, theoretical ice stream landsystems derived from geomorphological and sedimentological observations were developed to provide wider constraints on those interactions on palaeo-ice stream beds. Within these landsystems, the spatial distribution and formation processes of subglacial periodic bedforms transverse to the ice flow direction &amp;#8211; ribbed bedforms &amp;#8211; remain unclear. The purpose of this study is (i) to explore the conditions under which these ribbed bedforms develop and (ii) to constrain their spatial organisation along ice stream beds. &amp;#160;&lt;/p&gt;&lt;p&gt;We performed physical experiments with silicon putty (to simulate the ice), water (to simulate the meltwater) and sand (to simulate a soft sedimentary bed) to model the dynamics of ice streams and produce analog subglacial landsystems. We compare the results of these experiments with the distribution of ribbed bedforms on selected examples of palaeo-ice stream beds of the Laurentide Ice Sheet. Based on this comparison, we can draw several conclusions regarding the significance of ribbed bedforms in ice stream contexts:&lt;/p&gt;&lt;ul&gt;&lt;li&gt;Ribbed bedforms tend to form where the ice flow undergoes high velocity gradients and the ice-bed interface is unlubricated. Where the ribs initiate, we hypothesize that high driving stresses generate high basal shear stresses, accommodated through bed deformation of the active uppermost part of the bed.&lt;/li&gt; &lt;li&gt;Ribbed bedforms can develop subglacially from a flat sediment surface beneath shear margins (i.e., lateral ribbed bedforms) and stagnant lobes (i.e., submarginal ribbed bedforms) of ice streams, while they do not develop beneath surging lobes.&lt;/li&gt; &lt;li&gt;The orientation of ribbed bedforms reflects the local stress state along the ice-bed interface, with transverse bedforms formed by compression beneath ice lobes and oblique bedforms formed by transgression below lateral shear margins.&lt;/li&gt; &lt;li&gt;The development of ribbed bedforms where the ice-bed interface is unlubricated reveals distinctive types of discontinuous basal drainage systems below shear and lobe margins: linked-cavities and efficient meltwater channels respectively.&lt;/li&gt; &lt;/ul&gt;&lt;p&gt;Ribbed bedforms could thus constitute convenient geomorphic markers for the reconstruction of palaeo-ice stream margins, palaeo-ice flow dynamics and palaeo-meltwater drainage characteristics.&lt;/p&gt;

scholarly journals Coupled ice sheet–climate modeling under glacial and pre-industrial boundary conditions

2014 ◽  
Vol 10 (5) ◽  
pp. 1817-1836 ◽  
Author(s):  
F. A. Ziemen ◽  
C. B. Rodehacke ◽  
U. Mikolajewicz
Keyword(s):  
Boundary Conditions ◽  
General Circulation ◽  
Climate Modeling ◽  
Ice Sheets ◽  
Ice Sheet ◽  
General Circulation Models ◽  
Quasi Equilibrium ◽  
Ice Streams ◽  
Ice Stream ◽  
First Results

Abstract. In the standard Paleoclimate Modelling Intercomparison Project (PMIP) experiments, the Last Glacial Maximum (LGM) is modeled in quasi-equilibrium with atmosphere–ocean–vegetation general circulation models (AOVGCMs) with prescribed ice sheets. This can lead to inconsistencies between the modeled climate and ice sheets. One way to avoid this problem would be to model the ice sheets explicitly. Here, we present the first results from coupled ice sheet–climate simulations for the pre-industrial times and the LGM. Our setup consists of the AOVGCM ECHAM5/MPIOM/LPJ bidirectionally coupled with the Parallel Ice Sheet Model (PISM) covering the Northern Hemisphere. The results of the pre-industrial and LGM simulations agree reasonably well with reconstructions and observations. This shows that the model system adequately represents large, non-linear climate perturbations. A large part of the drainage of the ice sheets occurs in ice streams. Most modeled ice stream systems show recurring surges as internal oscillations. The Hudson Strait Ice Stream surges with an ice volume equivalent to about 5 m sea level and a recurrence interval of about 7000 yr. This is in agreement with basic expectations for Heinrich events. Under LGM boundary conditions, different ice sheet configurations imply different locations of deep water formation.

scholarly journals Deformation in Rutford Ice Stream, West Antarctica: measuring shear-wave anisotropy from icequakes

2013 ◽  
Vol 54 (64) ◽  
pp. 105-114 ◽  
Author(s):  
S.R. Harland ◽  
J.-M. Kendall ◽  
G.W. Stuart ◽  
G.E. Lloyd ◽  
A.F. Baird ◽  
...  
Keyword(s):  
Shear Wave ◽  
Flow Direction ◽  
Transversely Isotropic ◽  
Shear Wave Splitting ◽  
Ice Crystal ◽  
West Antarctica ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Stream ◽  
Wave Splitting

Abstract Ice streams provide major drainage pathways for the Antarctic ice sheet. The stress distribution and style of flow in such ice streams produce elastic and rheological anisotropy, which informs ice-flow modelling as to how ice masses respond to external changes such as global warming. Here we analyse elastic anisotropy in Rutford Ice Stream, West Antarctica, using observations of shear-wave splitting from three-component icequake seismograms to characterize ice deformation via crystal-preferred orientation. Over 110 high-quality measurements are made on 41 events recorded at five stations deployed temporarily near the ice-stream grounding line. To the best of our knowledge, this is the first well-documented observation of shear-wave splitting from Antarctic icequakes. The magnitude of the splitting ranges from 2 to 80 ms and suggests a maximum of 6% shear-wave splitting. The fast shear-wave polarization direction is roughly perpendicular to ice-flow direction. We consider three mechanisms for ice anisotropy: a cluster model (vertical transversely isotropic (VTI) model); a girdle model (horizontal transversely isotropic (HTI) model); and crack-induced anisotropy (HTI model). Based on the data, we can rule out a VTI mechanism as the sole cause of anisotropy – an HTI component is needed, which may be due to ice crystal a-axis alignment in the direction of flow or the alignment of cracks or ice films in the plane perpendicular to the flow direction. The results suggest a combination of mechanisms may be at play, which represent vertical variations in the symmetry of ice crystal anisotropy in an ice stream, as predicted by ice fabric models.

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