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

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.

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

Journal of Glaciology ◽

10.3189/s0022143000002732 ◽

1998 ◽

Vol 44 (147) ◽

pp. 405-418 ◽

Cited By ~ 2

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.

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

Journal of Glaciology ◽

10.1017/s0022143000002732 ◽

1998 ◽

Vol 44 (147) ◽

pp. 405-418 ◽

Cited By ~ 57

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.

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

Annals of Glaciology ◽

10.3189/1998aog27-1-182-186 ◽

1998 ◽

Vol 27 ◽

pp. 182-186 ◽

Cited By ~ 11

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.

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Meso- and microscale sea-ice motion in the East Siberian Sea as determined from ERS-1 SAR Data

Journal of Glaciology ◽

10.1017/s0022143000001878 ◽

1999 ◽

Vol 45 (150) ◽

pp. 370-383 ◽

Cited By ~ 7

Author(s):

Kim Morris ◽

Shusun Li ◽

Martin Jeffries

Keyword(s):

Time Series ◽

Sea Ice ◽

Large Scale ◽

Vector Fields ◽

Lateral Displacement ◽

Motion Vector ◽

Sar Interferometry ◽

East Siberian Sea ◽

Pack Ice ◽

Sar Data

Abstract Synthetic aperture radar- (SAR-)derived ice-motion vectors and SAR interferometry were used to study the sea-ice conditions in the region between the coast and 75° N (~ 560 km) in the East Siberian Sea in the vicinity of the Kolyma River. ERS-1 SAR data were acquired between 24 December 1993 and 30 March 1994 during the 3 day repeat Ice Phase of the satellite. The time series of the ice-motion vector fields revealed rapid (3 day) changes in the direction and displacement of the pack ice. Longer-term (≥ 1 month) trends also emerged which were related to changes in large-scale atmospheric circulation. On the basis of this time series, three sea-ice zones were identified: the near-shore, stationary-ice zone; a transitional-ice zone;and the pack-ice zone. Three 3 day interval and one 9 day interval interferometric sets (amplitude, correlation and phase diagrams) were generated for the end of December, the begining of February and mid-March. They revealed that the stationary-ice zone adjacent to the coast is in constant motion, primarily by lateral displacement, bending, tilting and rotation induced by atmospheric/oceanic forcing. The interferogram patterns change through time as the sea ice becomes thicker and a network of cracks becomes established in the ice cover. It was found that the major features in the interferograms were spatially correlated with sea-ice deformation features (cracks and ridges) and major discontinuities in ice thickness.

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A statistical fracture model for Antarctic ice shelves and glaciers

The Cryosphere ◽

10.5194/tc-12-3187-2018 ◽

2018 ◽

Vol 12 (10) ◽

pp. 3187-3213 ◽

Cited By ~ 3

Author(s):

Veronika Emetc ◽

Paul Tregoning ◽

Mathieu Morlighem ◽

Chris Borstad ◽

Malcolm Sambridge

Keyword(s):

Large Scale ◽

Damage Mechanics ◽

Ice Sheets ◽

Continuum Damage Mechanics ◽

Ice Shelf ◽

Ice Shelves ◽

Flow Models ◽

Iceberg Calving ◽

Antarctic Continent ◽

Average Success Rate

Abstract. Antarctica and Greenland hold enough ice to raise sea level by more than 65 m if both ice sheets were to melt completely. Predicting future ice sheet mass balance depends on our ability to model these ice sheets, which is limited by our current understanding of several key physical processes, such as iceberg calving. Large-scale ice flow models either ignore this process or represent it crudely. To model fractured zones, an important component of many calving models, continuum damage mechanics as well as linear fracture mechanics are commonly used. However, these methods have a large number of uncertainties when applied across the entire Antarctic continent because the models were typically tuned to match processes seen on particular ice shelves. Here we present an alternative, statistics-based method to model the most probable zones of the location of fractures and demonstrate our approach on all main ice shelf regions in Antarctica, including the Antarctic Peninsula. We can predict the location of observed fractures with an average success rate of 84 % for grounded ice and 61 % for floating ice and a mean overestimation error rate of 26 % and 20 %, respectively. We found that Antarctic ice shelves can be classified into groups based on the factors that control fracture location.

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

The Cryosphere ◽

10.5194/tc-14-17-2020 ◽

2020 ◽

Vol 14 (1) ◽

pp. 17-37 ◽

Cited By ~ 2

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.

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Stratigraphy, stable isotopes and salinity in multi-year sea ice from the rift area, south George VI Ice Shelf, Antarctic Peninsula

Journal of Glaciology ◽

10.3189/s0022143000005797 ◽

1991 ◽

Vol 37 (127) ◽

pp. 357-367

Author(s):

J.-L. Tison ◽

E. M. Morris ◽

R. Souchez ◽

J. Jouzel

Keyword(s):

Stable Isotopes ◽

Sea Ice ◽

Fresh Water ◽

Large Scale ◽

Sea Water ◽

Ice Core ◽

Ice Shelf ◽

The Core ◽

Brackish Ice ◽

Ice Production

AbstractResults from a detailed profile in a 5.54 m multi-year sea-ice core from the rift area in the southern part of George VI Ice Shelf are presented. Stratigraphy, stable isotopes and Na content are used to investigate the growth processes of the ice cover and to relate them to melting processes at the bottom of the ice shelf.The thickest multi-year sea ice in the sampling area appears to be second-year sea ice that has survived one melt season. Combined salinity/stable-isotope analyses show large-scale sympathetic fluctuations that can be related to the origin of the parent water. Winter accretion represents half of the core length and mainly consists of frazil ice of normal sea-water origin. However, five major dilution events of sea water, with fresh-water input from the melting base of the ice shelf reaching 20% on two occasions, punctuate this winter accretion. Two of them correspond to platelet-ice production, which is often related to the freezing of ascending supercooled water from the bottom of the ice shelf.Brackish ice occurs between 450 and 530 cm in the core. It is demonstrated that this results from the freezing of brackish water (Jeffries and others, 1989) formed by mixing of normal sea water with melted basal shelf ice, with dilution percentages of maximum 80% fresh water.

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

Journal of Glaciology ◽

10.1017/s0022143000006900 ◽

1986 ◽

Vol 32 (110) ◽

pp. 72-86 ◽

Cited By ~ 46

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.

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The Recent Advance of the Ross Ice Shelf Antarctica

Journal of Glaciology ◽

10.3189/s0022143000012181 ◽

1986 ◽

Vol 32 (112) ◽

pp. 464-474 ◽

Cited By ~ 1

Author(s):

S. S. Jacobs ◽

D. R. Macayeal ◽

J. L. Ardai

Keyword(s):

Large Scale ◽

Melting Rate ◽

Spreading Rate ◽

Ice Shelf ◽

Ice Shelves ◽

Ross Ice Shelf ◽

Front Position ◽

Iceberg Calving ◽

Basal Melting ◽

Available Information

AbstractThe seaward edge of the Ross Ice Shelf advanced northward at a minimum average velocity of 0.8 km a–1 between 1962 and 1985. That advance approximated velocities that have been obtained from glaciological data, indicating little recent wastage by iceberg calving. West of long. 178° E., the ice shelf has attained its most northerly position in the past 145 years, and has not experienced a major calving episode for at least 75 years. Since 1841 the ice-front position has advanced and retreated within a zone from about lat. 77° 10’S. (near long. 171° E.) to lat. 78° 40’ S. (near long. 164° W.). The central ice front is now farthest south but has the highest advance rate. Calving may occur at more frequent intervals in that sector, which also overlies the warmest ocean currents that flow into the sub-ice-shelf cavity. Available information on ice-shelf advance, thickness, spreading rate, and surface accumulation indicates a basal melting rate around 3 m a–1 near the ice front. These data and independent estimates imply that basal melting is nearly as large a factor as iceberg calving in maintaining the ice-shelf mass balance. In recent years, the Ross, Ronne, and Filchner Ice Shelves have contributed few icebergs to the Southern Ocean, while projections from a contemporaneous iceberg census are that circumpolar calving alone may exceed accumulation on the ice sheet. Large-scale ice-shelf calving may have preceded historical sightings of increased numbers of icebergs at sea.

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