scholarly journals Comparison of ice-shelf creep flow simulations with ice-front motion of Filchner-Ronne Ice Shelf, Antarctica, detected by SAR interferometry

1998 ◽  
Vol 27 ◽  
pp. 182-186 ◽  
Author(s):  
Christina L. Hulbe ◽  
Eric Rignot ◽  
Douglas R. Macayeal
Keyword(s):  
Sar Interferometry ◽  
Shear Strain Rate ◽  
Ice Shelf ◽  
Ice Flow ◽  
Flow Simulations ◽  
Creep Flow ◽  
Iceberg Calving ◽  
The Difference ◽  
Coastal Boundary ◽  
Flow Boundaries

Comparison between numerical model ice-shelf flow simulations and synthetic aperture radar (SAR) interferograms is used to study ice-flow dynamics at the Hemmen Ice Rise (HIR) and Lassiter Coast (LC) corners of the iceberg-calving front of the Filchnei—Ronne Ice Shelf, Antarctica. The interferograms are constructed from SAR images provided by the European Space Agency's remote-sensing satellites (ERS-1/2). Narrow bands of large shear strain rate are observed along the boundaries between fast-flowing ice-shelf ice and no-flow boundaries. Large rifts, opened where the ice shelf separates from the coast, appear to be filled with a melange of sea ice, ice-shelf fragments, and snow. Trial and error is used to find the best match between artificial interferograms, constructed from modelled ice flow, and the observed interferograms. We find that at both HIR and LC, ice with in the coastal boundary layers must be significantly softer than adjacent ice. At HIR the rift-filling ice melange transmits stress from one ice-shelf fragment to another; thus it must have mechanical competence and must moderate both separation of the ice shelf from the coast and the release of icebergs. However, the ice melange along the LC does not. The difference may be related to melange thickness, which could vary in the two locations due to differences in sub-ice-shelf oceanography or perhaps to regional atmospheric warming, currently under way along the Antarctic Peninsula. Future warming could weaken the melange ice around HIR as well, causing the ice shelf to lose contact with that shelf-front anchor.

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 Full-Stokes modeling of grounding line dynamics, ice melt and iceberg calving for Thwaites Glacier, West Antarctica

2016 ◽  
Author(s):  
Hongju Yu ◽  
Eric Rignot ◽  
Mathieu Morlighem ◽  
Helene Seroussi
Keyword(s):  
West Antarctica ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Melt ◽  
Linear Elastic ◽  
Grounding Line ◽  
Iceberg Calving ◽  
Elastic Fracture ◽  
The Difference ◽  
The Impact

Abstract. Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past three decades. Here we present a two-dimensional, Full-Stokes (FS) modeling study of the grounding line dynamics and iceberg calving of TG. First, we compare FS with two simplified models, the higher-order (HO) model and the shallow-shelf approximation (SSA) model, to determine the impact of changes in ice shelf basal melt rate on grounding line dynamics. Second, we combine FS with the Linear Elastic Fracture Mechanics (LEFM) theory to simulate crevasse propagation and iceberg calving. In the first experiment, we find that FS requires basal melt rate consistent with remote sensing observations to reach steady state at TG’s current geometry while HO and SSA require unrealistically high basal melt rate. The grounding line of FS is also more sensitive to changes in basal melt rate than HO and SSA. In the second experiment, we find that only FS can produce surface and bottom crevasses that match radar sounding observations of crevasse width and height. We attribute the difference to the non- hydrostatic conditions of ice near the grounding line, which facilitate crevasse formation and are not accounted for in HO and SSA. Additional experiments using FS indicate that iceberg calving is significantly enhanced when surface crevasses exist near the grounding line, when ice shelf is shortened, or when the ice shelf front is undercut. We conclude that FS yields substantial improvements in the description of ice flow dynamics at the grounding line under high basal melt rate and in constraining crevasse formation and iceberg calving.

scholarly journals Ice-shelf dynamics near the front of the Filchner—Ronne Ice Shelf, Antarctica, revealed by SAR interferometry

1998 ◽  
Vol 44 (147) ◽  
pp. 405-418 ◽  
Author(s):  
Eric Rignot ◽  
Douglas R. MacAyeal
Keyword(s):  
Large Scale ◽  
Sar Interferometry ◽  
Velocity Shear ◽  
Ocean Tide ◽  
Ice Shelf ◽  
Sar Images ◽  
Creep Flow ◽  
Iceberg Calving ◽  
Shelf Dynamics ◽  
Shelf Flow

AbstractFifteen synthetic aperture radar (SAR) images of the Ronne Ice Shelf (also referred to as the Filchner-Ronne Ice Shelf), Antarctica, obtained by the European remote-sensing satellites ERS-1 and -2, are used to study ice-shelf dynamics near two ends of the iceberg-calving front. Interferograms constructed from these SAR images are used to resolve the ice-shelf displacement along several directions in response to both ocean tide and long-term creep flow. Tidal motion is separated from creep flow using differential interferometry, i.e. two or more interferograms in which fringe patterns common to all are predominantly associated with creep flow. Creep-flow velocities thus determined compare well with prior ice-shelf velocity surveys. Using these data, we studied the influence of large-scale rifts, ice rises and coastal separation on the ice-shelf flow. Many of the large rifts that appear to form the boundaries where tabular icebergs may eventually detach from the ice shelf are filled with a melange of sea ice, ice-shelf debris and wind-blown snow. The interferograms show that this melange tends to deform coherently in response to the ice-shelf flow and has sufficient strength to trap large tabular ice-shelf fragments for several decades before the fragments eventually become icebergs. In many instances, the motion of the tabular fragments is a rigid-body rotation about a vertical axis that is driven by velocity shear within the melange. Tfhe mechanical role of the rift-filling melange may be to bind tabular ice-shelf fragments to the main ice shelf before they calve. This suggests two possible mechanisms by which climate could influence tabular iceberg calving. First, spatial gradients in oceanic and atmospheric temperature may determine where the melange melts and, thus, the location of the iceberg-caking margin. Second, melting or weakening of ice melange as a consequence of climate change could trigger a sudden or widespread release of tabular icebergs and lead to rapid ice-shelf disintegration.

scholarly journals Ice-shelf dynamics near the front of the Filchner—Ronne Ice Shelf, Antarctica, revealed by SAR interferometry

1998 ◽  
Vol 44 (147) ◽  
pp. 405-418 ◽  
Author(s):  
Eric Rignot ◽  
Douglas R. MacAyeal
Keyword(s):  
Large Scale ◽  
Sar Interferometry ◽  
Velocity Shear ◽  
Ocean Tide ◽  
Ice Shelf ◽  
Sar Images ◽  
Creep Flow ◽  
Iceberg Calving ◽  
Shelf Dynamics ◽  
Shelf Flow

AbstractFifteen synthetic aperture radar (SAR) images of the Ronne Ice Shelf (also referred to as the Filchner-Ronne Ice Shelf), Antarctica, obtained by the European remote-sensing satellites ERS-1 and -2, are used to study ice-shelf dynamics near two ends of the iceberg-calving front. Interferograms constructed from these SAR images are used to resolve the ice-shelf displacement along several directions in response to both ocean tide and long-term creep flow. Tidal motion is separated from creep flow using differential interferometry, i.e. two or more interferograms in which fringe patterns common to all are predominantly associated with creep flow. Creep-flow velocities thus determined compare well with prior ice-shelf velocity surveys. Using these data, we studied the influence of large-scale rifts, ice rises and coastal separation on the ice-shelf flow. Many of the large rifts that appear to form the boundaries where tabular icebergs may eventually detach from the ice shelf are filled with a melange of sea ice, ice-shelf debris and wind-blown snow. The interferograms show that this melange tends to deform coherently in response to the ice-shelf flow and has sufficient strength to trap large tabular ice-shelf fragments for several decades before the fragments eventually become icebergs. In many instances, the motion of the tabular fragments is a rigid-body rotation about a vertical axis that is driven by velocity shear within the melange. Tfhe mechanical role of the rift-filling melange may be to bind tabular ice-shelf fragments to the main ice shelf before they calve. This suggests two possible mechanisms by which climate could influence tabular iceberg calving. First, spatial gradients in oceanic and atmospheric temperature may determine where the melange melts and, thus, the location of the iceberg-caking margin. Second, melting or weakening of ice melange as a consequence of climate change could trigger a sudden or widespread release of tabular icebergs and lead to rapid ice-shelf disintegration.

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 Recent rift formation and impact on the structural integrity of the Brunt Ice Shelf, East Antarctica

2018 ◽  
Vol 12 (2) ◽  
pp. 505-520 ◽  
Author(s):  
Jan De Rydt ◽  
G. Hilmar Gudmundsson ◽  
Thomas Nagler ◽  
Jan Wuite ◽  
Edward C. King
Keyword(s):  
Natural Experiment ◽  
Flow Model ◽  
Structural Integrity ◽  
East Antarctica ◽  
Heterogeneous Structure ◽  
High Likelihood ◽  
Ice Shelf ◽  
Ice Flow ◽  
Iceberg Calving ◽  
Slow Propagation

Abstract. We report on the recent reactivation of a large rift in the Brunt Ice Shelf, East Antarctica, in December 2012 and the formation of a 50 km long new rift in October 2016. Observations from a suite of ground-based and remote sensing instruments between January 2000 and July 2017 were used to track progress of both rifts in unprecedented detail. Results reveal a steady accelerating trend in their width, in combination with alternating episodes of fast ( > 600 m day−1) and slow propagation of the rift tip, controlled by the heterogeneous structure of the ice shelf. A numerical ice flow model and a simple propagation algorithm based on the stress distribution in the ice shelf were successfully used to hindcast the observed trajectories and to simulate future rift progression under different assumptions. Results show a high likelihood of ice loss at the McDonald Ice Rumples, the only pinning point of the ice shelf. The nascent iceberg calving and associated reduction in pinning of the Brunt Ice Shelf may provide a uniquely monitored natural experiment of ice shelf variability and provoke a deeper understanding of similar processes elsewhere in Antarctica.

scholarly journals The imbalance of glaciers after disintegration of Larsen B ice shelf, Antarctic Peninsula

2010 ◽  
Vol 4 (3) ◽  
pp. 1607-1633 ◽  
Author(s):  
H. Rott ◽  
F. Müller ◽  
T. Nagler ◽  
D. Floricioiu
Keyword(s):  
High Resolution ◽  
Antarctic Peninsula ◽  
Ice Shelf ◽  
Ice Flow ◽  
Flow Acceleration ◽  
Radar Images ◽  
Glacier Front ◽  
High Resolution Radar ◽  
The Difference ◽  
Main Factor

Abstract. The outlet glaciers to the embayment of the Larsen B Ice Shelf started to accelerate soon after the ice shelf disintegrated in March 2002. We analyse high resolution radar images of the TerraSAR-X satellite, launched in June 2007, to map the motion of outlet glaciers in detail. The frontal velocities are used to estimate the calving fluxes for 2008/2009. As reference for pre-collapse conditions, when the glaciers were in balanced state, the ice fluxes through the same gates are computed using ice motion maps derived from interferometric data of the ERS-1/ERS-2 satellites in 1995 and 1999. The difference between the pre- and post-collapse fluxes provides an estimate on the mass imbalance. For the Larsen-B embayment the 2008 mass deficit is estimated at 5.94 ± 1.55 Gt/yr, significantly lower than previously published values. The ice flow acceleration follows a similar pattern on the various glaciers, being initiated at the calving terminus. The acceleration extends far upstream, gradually decreasing in magnitude with distance from the front. This suggests stress perturbation at the glacier front being a main factor for acceleration. So far there are no signs of slow-down indicating that dynamic thinning and frontal retreat will go on.

scholarly journals Recent rift formation and impact on the structural integrity of the Brunt Ice Shelf, East Antarctica

2017 ◽  
Author(s):  
Jan De Rydt ◽  
G. Hilmar Gudmundsson ◽  
Thomas Nagler ◽  
Jan Wuite ◽  
Edward C. King
Keyword(s):  
Natural Experiment ◽  
Flow Model ◽  
Structural Integrity ◽  
East Antarctica ◽  
Heterogeneous Structure ◽  
Ice Shelf ◽  
Ice Flow ◽  
Iceberg Calving ◽  
Simple Fracture ◽  
Slow Propagation

Abstract. We report on the recent reactivation of a large chasm in the Brunt Ice Shelf, East Antarctica, in December 2012, and the formation of a 50-km long new rift in October 2016. Observations from a suite of ground based and remote sensing instruments between January 2000 and July 2017 were used to track progress of both cracks in unprecedented detail. Results reveal a steady accelerating trend in the widening of the rifts, in combination with alternating episodes of fast (> 600 m/day) and slow propagation of the crack tip, controlled by the heterogeneous structure of the ice shelf. A numerical ice-flow model and a simple fracture propagation criterion were successfully used to hindcast the observed trajectories, and to simulate future rift progression under different assumptions, showing a high likelihood of ice loss at the McDonald Ice Rumples, the only pinning point of the ice shelf. The nascent iceberg calving and associated reduction in pinning of the Brunt Ice Shelf may provide a uniquely monitored natural experiment of ice shelf variability, and provoke a deeper understanding of similar processes elsewhere in Antarctica.

scholarly journals The imbalance of glaciers after disintegration of Larsen-B ice shelf, Antarctic Peninsula

2011 ◽  
Vol 5 (1) ◽  
pp. 125-134 ◽  
Author(s):  
H. Rott ◽  
F. Müller ◽  
T. Nagler ◽  
D. Floricioiu
Keyword(s):  
Cross Sections ◽  
Ice Shelf ◽  
Laser Altimetry ◽  
Ice Flow ◽  
Flow Acceleration ◽  
Radar Images ◽  
Glacier Front ◽  
High Resolution Radar ◽  
The Difference ◽  
Main Factor

Abstract. The outlet glaciers to the embayment of the Larsen-B Ice Shelf started to accelerate soon after the ice shelf disintegrated in March 2002. We analyse high resolution radar images of the TerraSAR-X satellite, launched in June 2007, to map the motion of outlet glaciers in detail. The frontal velocities are used to estimate the calving fluxes for 2008/2009. As reference for pre-collapse conditions, when the glaciers were in balanced state, the ice fluxes through the same gates are computed using ice motion maps derived from interferometric data of the ERS-1/ERS-2 satellites in 1995 and 1999. Profiles of satellite laser altimetry from ICESat, crossing the terminus of several glaciers, indicate considerable glacier thinning between 2003 and 2007/2008. This is taken into account for defining the calving cross sections. The difference between the pre- and post-collapse fluxes provides an estimate on the mass imbalance. For the Larsen-B embayment the 2008 mass deficit is estimated at 4.34 ± 1.64 Gt a−1, significantly lower than previously published values. The ice flow acceleration follows a similar pattern on the various glaciers, gradually decreasing in magnitude with distance upstream from the calving front. This suggests stress perturbation at the glacier front being the main factor for acceleration. So far there are no signs of slow-down indicating that dynamic thinning and frontal retreat will go on.

scholarly journals Nivlisen, an Antarctic ice shelf in Dronning Maud Land: geodetic–glaciological results from a combined analysis of ice thickness, ice surface height and ice-flow observations

2006 ◽  
Vol 52 (176) ◽  
pp. 17-30 ◽  
Author(s):  
Martin Horwath ◽  
Reinhard Dietrich ◽  
Michael Baessler ◽  
Uwe Nixdorf ◽  
Daniel Steinhage ◽  
...  
Keyword(s):  
Mass Balance ◽  
Atlantic Coast ◽  
Sar Interferometry ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Equilibrium Relation ◽  
Ice Flow ◽  
Near Surface ◽  
Ice Surface ◽  
Ground Penetrating

AbstractExtensive observations on Nivlisen, an ice shelf on Antarctica’s Atlantic coast, are analyzed and combined to obtain a new description of its complex glaciological regime. We generate models of ice thickness (primarily from ground-penetrating radar), ellipsoidal ice surface height (primarily from ERS-1 satellite altimetry), freeboard height (by utilizing precise sea surface information) and ice-flow velocity (from ERS-1/-2 SAR interferometry and GPS measurements). Accuracy assessments are included. Exploiting the hydrostatic equilibrium relation, we infer the ‘apparent air layer thickness’ as a useful measure for a glacier’s density deviation from a pure ice body. This parameter exhibits a distinct spatial variation (ranging from ≈2 to ≈16m) which we attribute to the transition from an ablation area to an accumulation area. We compute mass-flux and mass-balance parameters on a local and areally integrated scale. The combined effect of bottom mass balance and temporal change averaged over an essential part of Nivlisen is –654 ± 170 kg m–2 a–1, which suggests bottom melting processes dominate. We discuss our results in view of temporal ice-mass changes (including remarks on historical observations), basal processes, near-surface processes and ice-flow dynamical features. The question of temporal changes remains open from the data at hand, and we recommend further observations and analyses for its solution.

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