Plane and Radial Ice-Shelf Flow with Prescribed Temperature Profile

1987 ◽  
pp. 117-140 ◽  
Author(s):  
L. W. Morland ◽  
R. Zainuddin
Keyword(s):  
Temperature Profile ◽  
Ice Shelf ◽  
Shelf Flow

scholarly journals Mapping ice-shelf flow with interferometric synthetic aperture radar stacking

2012 ◽  
Vol 58 (208) ◽  
pp. 265-277 ◽  
Author(s):  
Malcolm McMillan ◽  
Andrew Shepherd ◽  
Noel Gourmelen ◽  
Jeong-Won Park ◽  
Peter Nienow ◽  
...  
Keyword(s):  
Synthetic Aperture Radar ◽  
Atmospheric Pressure ◽  
Synthetic Aperture ◽  
Ocean Tide ◽  
Interferometric Synthetic Aperture Radar ◽  
West Antarctica ◽  
Ice Shelf ◽  
Flow Displacement ◽  
Shelf Flow ◽  
Aperture Radar

AbstractInterferometric synthetic aperture radar (InSAR) observations of ice-shelf flow contain ocean-tide and atmospheric-pressure signals. A model-based correction can be applied, but this method is limited by its dependency upon model accuracy, which in remote regions can be uncertain. Here we describe a method to determine two-dimensional ice-shelf flow vectors independently of model predictions of tide and atmospheric pressure, by stacking conventional and multiple aperture InSAR (MAI) observations of the Dotson Ice Shelf, West Antarctica. In this way we synthesize a longer observation period, which enhances long-period (flow) displacement signals, relative to rapidly varying (tide and atmospheric pressure) signals and noise. We estimate the error associated with each component of the velocity field to be ~22 ma-1, which could be further reduced if more images were available to stack. With the upcoming launch of several satellite missions, offering the prospect of regular short-repeat SAR acquisitions, this study demonstrates that stacking can improve estimates of ice-shelf flow velocity.

scholarly journals Exploring mechanisms responsible for tidal modulation in flow of the Filchner–Ronne Ice Shelf

2020 ◽  
Vol 14 (1) ◽  
pp. 17-37 ◽  
Author(s):  
Sebastian H. R. Rosier ◽  
G. Hilmar Gudmundsson
Keyword(s):  
Large Scale ◽  
Elastic Response ◽  
Lateral Migration ◽  
Ice Shelf ◽  
Ice Flow ◽  
Flow Perturbation ◽  
Long Period ◽  
Shelf Slope ◽  
Short Period ◽  
Shelf Flow

Abstract. An extensive network of GPS sites on the Filchner–Ronne Ice Shelf and adjoining ice streams shows strong tidal modulation of horizontal ice flow at a range of frequencies. A particularly strong (horizontal) response is found at the fortnightly (Msf) frequency. Since this tidal constituent is absent in the (vertical) tidal forcing, this observation implies the action of some non-linear mechanism. Another striking aspect is the strong amplitude of the flow perturbation, causing a periodic reversal in the direction of ice shelf flow in some areas and a 10 %–20 % change in speed at grounding lines. No model has yet been able to reproduce the quantitative aspects of the observed tidal modulation across the entire Filchner–Ronne Ice Shelf. The cause of the tidal ice flow response has, therefore, remained an enigma, indicating a serious limitation in our current understanding of the mechanics of large-scale ice flow. A further limitation of previous studies is that they have all focused on isolated regions and interactions between different areas have, therefore, not been fully accounted for. Here, we conduct the first large-scale ice flow modelling study to explore these processes using a viscoelastic rheology and realistic geometry of the entire Filchner–Ronne Ice Shelf, where the best observations of tidal response are available. We evaluate all relevant mechanisms that have hitherto been put forward to explain how tides might affect ice shelf flow and compare our results with observational data. We conclude that, while some are able to generate the correct general qualitative aspects of the tidally induced perturbations in ice flow, most of these mechanisms must be ruled out as being the primary cause of the observed long-period response. We find that only tidally induced lateral migration of grounding lines can generate a sufficiently strong long-period Msf response on the ice shelf to match observations. Furthermore, we show that the observed horizontal short-period semidiurnal tidal motion, causing twice-daily flow reversals at the ice front, can be generated through a purely elastic response to basin-wide tidal perturbations in the ice shelf slope. This model also allows us to quantify the effect of tides on mean ice flow and we find that the Filchner–Ronne Ice Shelf flows, on average, ∼ 21 % faster than it would in the absence of large ocean tides.

scholarly journals Ice-shelf dynamics near the front of the Filchner-Ronne Ice Shelf, Antaretica, revealed by SAR interferometry: model/interferogram comparison

1998 ◽  
Vol 44 (147) ◽  
pp. 419-428 ◽  
Author(s):  
Douglas R MacAyeal ◽  
Eric Rignot ◽  
Christina L Hulbe
Keyword(s):  
Sea Ice ◽  
Large Scale ◽  
Sar Interferometry ◽  
Deformation Pattern ◽  
Ice Shelf ◽  
Mechanical Coupling ◽  
Iceberg Calving ◽  
Shelf Dynamics ◽  
Coastal Boundary ◽  
Shelf Flow

AbstractWe compare European remote-sensing satellite (ERS) synthetic aperture radar interferograms with artificial interferograms constructed using output of a finite-element ice-shelf flow model to study the dynamics of Filchner-Ronne Ice Shelf (FRIS), Antaretica, near Hemmen Ice Rise (HIR) where the iceberg-calving front intersects Berkner Island. We find that the model must account for rifts, mechanically competent sea ice which fills rifts, and ice softening in coastal boundary layers in order to agree with the ice-deformation pattern implied by observed interferograms. Analysis of the stress field in the model experiment that best matches the observed interferograms suggests that: (1) HIR introduces weakness into the ice shelf through the generation of large-scale rifts, and (2) the melange of sea ice and ice-shelf fragments that fills the rifts stabilizes the shelf front by providing mechanical coupling between the fractured shelf front and the adjacent coast. The rift-filling melange could melt more easily than the surrounding ice shelf and thus could represent a vulnerability of the FRIS to climate warming.

scholarly journals Influence of pre-existing microstructure on mechanical properties of marine ice during compression experiments

2014 ◽  
Vol 60 (221) ◽  
pp. 576-586 ◽  
Author(s):  
Marie Dierckx ◽  
Mark Peternell ◽  
Christian Schroeder ◽  
Jean-Louis Tison
Keyword(s):  
Rheological Properties ◽  
Rheological Behaviour ◽  
Secondary Creep ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Before And After ◽  
Weak Points ◽  
The Given ◽  
Shelf Flow ◽  
Range Of Values

AbstractMarine ice is an important component of ice shelves in Antarctica. It accretes in substantial amounts at weak points and below ice shelves. It is likely to exhibit peculiar rheological properties, which are crucial to understanding its potential role in stabilizing ice-shelf flow. Due to its location and consolidation processes, marine ice can present a variety of textures which are likely to influence its rheological properties. We present a new dataset of unconfined uniaxial compression experiments on folded marine ice samples that have been cut at various angles to the folds. Texture and fabric analyses are described ‘before’ and ‘after’ the deformation experiment. It is shown that, in the given stress configuration, the geometry of the anisotropy controls the rheological behaviour of the marine ice. During secondary creep, folded marine ice is harder to deform than weakly textured ice when compressed parallel or perpendicular to the folds' hinges, while the reverse is true for ice compressed at 45°. The observed range of values for the n exponent in Glen's flow law is between 2.1 and 4.1. Surprisingly, we see that tertiary creep tends to develop at a higher total strain than for randomly oriented impurity-free meteoric ice.

scholarly journals A Time-Dependent Simulation of the Ross Ice Shelf Flow (Abstract)

1984 ◽  
Vol 5 ◽  
pp. 217-219 ◽  
Author(s):  
Douglas R. MacAyeal ◽  
Robert H. Thomas
Keyword(s):  
Element Model ◽  
Momentum Balance ◽  
Ice Shelf ◽  
Time Step ◽  
Ross Ice Shelf ◽  
Time Marching ◽  
Accelerate Convergence ◽  
Spreading Rates ◽  
Shelf Flow ◽  
The Finite Element Model

The finite-element model discussed by MacAyeal and Thomas (1982) has been improved to include solution of the heat equation within each element, and to accelerate convergence to solution of the momentum-balance equations in terms of ice-shelf spreading rates. The model is now sufficiently rapid to permit both snapshot and time-marching simulations of a large ice shelf at high spatial and temporal resolution (grid size 10 km; time step 0.1 a). Here, we describe three model simulations of Ross Ice Shelf behavior.

scholarly journals The Effects of Basal Melting on the Present Flow of the Ross Ice Shelf, Antarctica

1986 ◽  
Vol 32 (110) ◽  
pp. 72-86 ◽  
Author(s):  
D.R. MacAyeal ◽  
R.H. Thomas
Keyword(s):  
Large Scale ◽  
Oceanic Circulation ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ross Ice Shelf ◽  
Flow And Heat Transfer ◽  
Improve Model ◽  
Dependent Flow ◽  
Basal Melting ◽  
Shelf Flow

AbstractWe use a hybrid finite-element/finite-difference model of ice-shelf flow and heat transfer to investigate the effects of basal melting on the present observed flow of the Ross Ice Shelf, Two hypothetical basal melting scenarios are compared: (i) zero melting everywhere and (ii) melting sufficient to balance any large-scale patterns of ice-shelf thickening that would otherwise occur. As a result of the temperature-dependent flow law (which we idealize as having a constant activation energy of 120 kJ mol−1, a scaling coefficient of 1.3 N m−2s1/3, and an exponent of 3), simulated ice-shelf velocities for the second scenario are reduced by up to 20% below those of the first. Our results support the hypothesis that melting patterns presently maintain ice thickness in steady state and conform to patterns of oceanic circulation presently thought to ventilate the sub-ice cavity. Differences between the simulated and observed velocities are too large in the extreme south-eastern quarter of the ice shelf to permit verification of either basal melting scenario. These differences highlight the need to improve model boundary conditions at points where ice streams feed the ice shelf and where the ice shelf meets stagnant grounded ice.

scholarly journals Exploring mechanisms responsible for tidal modulation in flow of the Filchner-Ronne Ice Shelf

2019 ◽  
Author(s):  
Sebastian H. R. Rosier ◽  
G. Hilmar Gudmundsson
Keyword(s):  
Large Scale ◽  
Elastic Response ◽  
Lateral Migration ◽  
Ice Shelf ◽  
Ice Flow ◽  
Flow Perturbation ◽  
Tidal Motion ◽  
Shelf Slope ◽  
Shelf Flow ◽  
Tidal Response

Abstract. An extensive network of GPS sites on the Filchner-Ronne Ice Shelf and adjoining ice streams show strong tidal modulation of horizontal ice flow at a range of frequencies. A particularly strong (horizontal) response is found at the fortnightly (Msf) frequency. Since this tidal constituent is absent in the (vertical) tidal forcing, this observation implies the action of some nonlinear mechanism. Another striking aspect is the strong amplitude of the flow perturbation, causing a periodic reversal in the direction of ice shelf flow in some areas, and a 10–20 % change in speed at grounding lines. No model has yet been able to reproduce the quantitative aspects of the observed tidal modulation on the Filchner-Ronne Ice Shelf. The cause of the tidal response has therefore remained an enigma, indicating a serious limitation in our current understanding of the mechanics of large-scale ice flow. A further limitation of previous studies is that they have all focused on isolated regions and interactions between different areas have, therefore, not been fully accounted for. Here, we conduct the first large-scale ice-flow modelling study to explore these processes using a viscoelastic rheology and realistic geometry of the entire Filchner-Ronne ice shelf, where the best observations of tidal response are available. We evaluate all the relevant mechanisms that have hitherto been put forward to explain how tides might affect ice-shelf flow and compare our results with observational data. We conclude that, while some are able to generate the correct general qualitative aspects of the tidally-induced perturbations in ice flow, most of these mechanisms must be ruled out as being the primary cause of the large observed nonlinear response. We find that only tidally-induced lateral migration of grounding lines can generate a sufficiently strong long-periodic Msf response on the ice shelf to match observations. Furthermore, we show that the observed short-periodic diurnal tidal motion, causing twice-daily flow reversals at the ice front, can be generated through a purely elastic response to basin-wide tidal perturbations in the ice shelf slope. This model also allows us to quantify the effect of tides on mean ice flow and we find that the Filchner-Ronne Ice Shelf flows on average ~ 21 % faster than it would in the absence of large ocean tides.

scholarly journals Sheet, stream, and shelf flow as progressive ice-bed uncoupling: Byrd Glacier, Antarctica, and Jakobshavn Isbrae, Greenland

2015 ◽  
Vol 9 (4) ◽  
pp. 4271-4354
Author(s):  
T. Hughes ◽  
A. Sargent ◽  
J. Fastook ◽  
K. Purdon ◽  
J. Li ◽  
...  
Keyword(s):  
Stream Flow ◽  
Stokes Equations ◽  
Force Balance ◽  
Navier Stokes ◽  
Ice Shelf ◽  
Sheet Flow ◽  
Lower Yield ◽  
Navier Stokes Equations ◽  
Basal Ice ◽  
Shelf Flow

Abstract. The first-order control of ice thickness and height above sea level is linked to the decreasing strength of ice-bed coupling alone flowlines from an interior ice divide to the calving front of an ice shelf. Uncoupling progresses as a frozen bed progressively thaws for sheet flow, as a thawed bed is progressively drowned for stream flow, and as lateral and/or local grounding vanish for shelf flow. This can reduce ice thicknesses by 90 % and ice elevations by 99 % along flowlines. Original work presented here includes (1) replacing flow and sliding laws for sheet flow with upper and lower yield stresses for creep in cold overlying ice and basal ice sliding over deforming till, respectively, (2) replacing integrating the Navier–Stokes equations for stream flow with geometrical solutions to the force balance, and (3) including resistance to shelf flow caused by lateral confinement in a fjord and local grounding at ice rumples and ice rises. A comparison is made between our approach and two approaches based on continuum mechanics. Applications are made to Byrd Glacier in Antarctica and Jakobshavn Isbrae in Greenland.

scholarly journals A thermomechanical model of ice-shelf flow

1996 ◽  
Vol 23 ◽  
pp. 13-20 ◽  
Author(s):  
Vincent Rommelaere ◽  
Catherine Ritz
Keyword(s):  
Small Island ◽  
Numerical Techniques ◽  
Ice Shelf ◽  
Thermomechanical Model ◽  
Grounding Line ◽  
Shelf Flow

An ice-shelf model which features efficient numerical techniques is developed to determine the back-force exerted by sides and pinning points, such as islands of an embayed ice shelf. The model is applied to three ideal geometries and shows that the restraint exerted by a small island, even far downstream from the grounding line, can represent about one-half of the total restraint due to the embayment. Our results are further interpreted to suggest several criteria useful for testing any ice-shelf model.

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