The use of tiltmeters to study the dynamics of Antarctic ice-shelf grounding lines

Abstract New tiltmeter data are presented from Doake Ice Rumples on Ronne Ice Shelf, Antarctica. Five sites which showed a tidal ice-shelf flexure have been analysed using an elastic beam model to investigate the variation of flexure amplitude with distance from the grounding line. An earlier study on Rutford Ice Stream which also used an elastic model required an ice thickness much less than that observed. Reworking the Rutford Ice Stream data suggests that this greatly reduced ice thickness is not required, given the current sparse data coverage. The elastic model is used to improve the estimated grounding-line position on Rutford Ice Stream. Some of the difficulties in modelling ice-shelf flexure and locating grounding lines are discussed.

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New ice thickness maps of Filchner–Ronne Ice Shelf, Antarctica, with specific focus on grounding lines and marine ice

Antarctic Science ◽

10.1017/s0954102007000661 ◽

2007 ◽

Vol 19 (4) ◽

pp. 521-532 ◽

Cited By ~ 40

Author(s):

A. Lambrecht ◽

H. Sandhäger ◽

D.G. Vaughan ◽

C. Mayer

Keyword(s):

Surface Elevation ◽

Small Scale ◽

Ice Thickness ◽

Line Position ◽

Ice Shelf ◽

Ice Surface ◽

Seismic Sounding ◽

Grounding Line ◽

Data Coverage

AbstractFor the Filchner–Ronne Ice Shelf we have compiled measurements of meteoric ice thickness from many institutions, and several different techniques (e.g. radar and seismic sounding) to produce an improved digital map of meteoric ice thickness. This map has high-resolution compared to previous compilations and serves to highlight small-scale geographic features (e.g. ice plains, grounding-line regions). We have also produced a map of the thickness of marine ice bodies beneath the ice shelf by using borehole density data to calibrate an ice thickness to surface-elevation relation, and then comparing maps of ice surface elevation and meteoric ice thickness to infer marine ice thickness. Due to denser data coverage and the improved density-depth relation, the resulting map is a significant improvement on its predecessors and allows insight into the glaciological context of the ice shelf, in particular, into the location of the grounding lines on the southern Ronne Ice Shelf. Here the data were supplemented with barometric determination of surface elevation, which were used to locate the grounding line position. The final delineation of the grounding line position was confirmed by reference to satellite imagery, and revealed that earlier estimates were substantially in error, especially in the area of Foundation Ice Stream and Möllereisstrom.

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On the representation of ice-shelf grounding zones in SAR interferograms

Journal of Glaciology ◽

10.3189/172756502781831197 ◽

2002 ◽

Vol 48 (162) ◽

pp. 345-356 ◽

Cited By ~ 16

Author(s):

Bernhard T. Rabus ◽

Oliver Lang

Keyword(s):

Elastic Beam ◽

Ice Thickness ◽

Beam Model ◽

Ice Shelf ◽

Ice Shelves ◽

One Dimensional ◽

West Antarctic ◽

Grounding Line ◽

The One ◽

Differential Interferogram

AbstractWe investigate limitations of the one-dimensional elastic-beam model to detect grounding line and thickness of an ice shelf from a differential interferogram. Spatial limitations due to grounding-line curvature and variable ice thickness are analyzed by comparison with two-dimensional plate flexure. Temporal limitations from the tide-dependent shift of the grounding line are analyzed by superpositions of four tidal flexure profiles representing differential interferograms. (i) At scales greater than one ice thickness, seaward protrusions of the grounding line are well represented by the elastic-beam model, while landward embayments of the same scale produce significant misplacements >10% of the ice thickness. (ii) For reasonable spatial variations of shelf thickness, the elastic-beam model gives reliable estimates of grounding-line position and unfractured mean ice thickness near the grounding line. (iii) For about 20% of superpositions of four tidal flexure profiles, the resulting grounding-line misplacements exceed the physical tidal shift of the grounding line by factors >2. For differential tide levels <10% of a 1 m tide dynamics, a physical shift of the grounding line of 0.3 km per metre of tide can lever misplacements of >2 km. Examples of real interferometric profiles from West Antarctic ice shelves corroborate our results.

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On the interpretation of ice-shelf flexure measurements

Journal of Glaciology ◽

10.1017/jog.2017.44 ◽

2017 ◽

Vol 63 (241) ◽

pp. 783-791 ◽

Cited By ~ 10

Author(s):

SEBASTIAN H. R. ROSIER ◽

OLIVER J. MARSH ◽

WOLFGANG RACK ◽

G. HILMAR GUDMUNDSSON ◽

CHRISTIAN T. WILD ◽

...

Keyword(s):

Elastic Beam ◽

Beam Theory ◽

Beam Model ◽

Line Position ◽

Ice Shelf ◽

Study Region ◽

Grounding Line ◽

Modelling Studies ◽

Bed Slope ◽

Viscoelastic Modelling

ABSTRACTTidal flexure in ice shelf grounding zones has been used extensively in the past to determine grounding line position and ice properties. Although the rheology of ice is viscoelastic at tidal loading frequencies, most modelling studies have assumed some form of linear elastic beam approximation to match observed flexure profiles. Here we use density, radar and DInSAR measurements in combination with full-Stokes viscoelastic modelling to investigate a range of additional controls on the flexure of the Southern McMurdo Ice Shelf. We find that inclusion of observed basal crevasses and density dependent ice stiffness can greatly alter the flexure profile and yet fitting a simple elastic beam model to that profile will still produce an excellent fit. Estimates of the effective Young's modulus derived by fitting flexure profiles are shown to vary by over 200% depending on whether these factors are included, even when the local thickness is well constrained. Conversely, estimates of the grounding line position are relatively insensitive to these considerations for the case of a steep bed slope in our study region. By fitting tidal amplitudes only, and ignoring phase information, elastic beam theory can provide a good fit to observations in a wide variety of situations. This should, however, not be taken as an indication that the underlying rheological assumptions are correct.

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The location of the grounding zone of Evans Ice Stream, Antarctica, investigated using SAR interferometry and modelling

Annals of Glaciology ◽

10.3189/172756409789624292 ◽

2009 ◽

Vol 50 (52) ◽

pp. 35-40 ◽

Cited By ~ 17

Author(s):

Helena J. Sykes ◽

Tavi Murray ◽

Adrian Luckman

Keyword(s):

Stream Flow ◽

Elastic Beam ◽

Tidal Height ◽

Sar Interferometry ◽

Beam Model ◽

West Antarctica ◽

Tidal Model ◽

Tidal Forcing ◽

Ice Stream ◽

Grounding Line

AbstractEvans Ice Stream, West Antarctica, has five tributaries and a complex grounding zone. The grounding zone of Evans Ice Stream, between the landward and seaward limits of tidal flexing, was mapped using SAR interferometry. The width of the mapped grounding zone was compared with that derived from an elastic beam model, and the tidal height changes derived from interferometry were compared with the results of a tidal model. Results show that in 1994 and 1996 the Evans grounding zone was located up to 100 km upstream of its location in the BEDMAP dataset. The grounding line of Evans Ice Stream is subjected to 5 m vertical tidal forcing, which would clearly affect ice-stream flow.

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Thinning and Grounding-Line Retreat on Ross Ice Shelf, Antarctica

Annals of Glaciology ◽

10.3189/s0260305500006492 ◽

1988 ◽

Vol 11 ◽

pp. 165-172 ◽

Cited By ~ 6

Author(s):

R. H. Thomas ◽

S. N. Stephenson ◽

R. A. Bindschadler ◽

S. Shabtaie ◽

C. R. Bentley

Keyword(s):

Snow Accumulation ◽

Gravity Potential ◽

Ice Thickness ◽

Ice Shelf ◽

Ross Ice Shelf ◽

Major Activity ◽

Ice Stream ◽

Grounding Line ◽

Ice Stream B ◽

Basal Melting

Detailed measurements of surface topography, ice motion, snow accumulation, and ice thickness were made in January 1974 and again in December 1984, along an 8 km stake network extending from the ice sheet, across the grounding line, and on to floating ice shelf in the mouth of slow-moving Ice Stream C, which flows into the eastern side of Ross Ice Shelf, Antarctica. During the 11 years between surveys, the grounding line retreated by approximately 300 m. This was caused by net thinning of the ice shelf, which we believe to be a response to the comparatively recent, major decrease in ice discharge from Ice Stream C. Farther inland, snow accumulation is not balanced by ice discharge, and the ice stream is growing progressively thicker.There is evidence that the adjacent Ice Stream B has slowed significantly over the last decade, and this may be an early indication that this fast-moving ice stream is about to enter a period of stagnation similar to that of Ice Stream C. Indeed, these large ice streams flowing from West Antarctica into Ross Ice Shelf may oscillate between periods of relative stagnation and major activity. During active periods, large areas of ice shelf thicken and run aground on seabed to form extensive “ice plains” in the mouth of the ice stream. Ultimately, these become too large to be pushed seaward by the ice stream, which then slows down and enters a period of stagnation. During this period, the grounding line of the ice plain retreats, as we observe today in the mouth of Ice Stream C, because nearby ice shelf, no longer compressed by ice-stream motion, progressively thins. At the same time, water within the deformable till beneath the ice starts to freeze on to the base of the ice stream, and snow accumulation progressively increases the ice thickness. A new phase of activity would be initiated when the increasing gravity potential of the ice stream exceeds the total resistance of the shrinking ice plain and the thinning layer of deformable till at the bed. This could occur rapidly if the effects of the shrinking ice plain outweigh those of the thinning (and therefore stiffening) till. Otherwise, the till layer would finally become completely frozen, and the ice stream would have to thicken sufficiently to initiate significant heating by internal deformation, followed by basal melting and finally saturation of an adequate thickness of till; this could take some thousands of years.

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Radio Echo-Sounding of Riiser-Larsenisen (Abstract only)

Annals of Glaciology ◽

10.3189/s0260305500003347 ◽

1982 ◽

Vol 3 ◽

pp. 355-355 ◽

Cited By ~ 2

Author(s):

Olav Orheim

Keyword(s):

Outer Part ◽

Ice Thickness ◽

Horizontal Distance ◽

Ice Shelf ◽

Ice Stream ◽

Grounding Line ◽

Radio Echo Sounding ◽

Polar Research Institute ◽

Antarctic Research ◽

Echo Sounding

The Norwegian Antarctic Research Expedition 1978–79 used the Scott Polar Research Institute Mk IV radio echo-sounding system fitted in a Bell 206B helicopter to survey 620 km of Riiser-Larsenisen and 100 km across the outer part of Stancomb-Wills Ice Stream. Observed thicknesses of Riiser-Larsenisen decrease from 700 m at the grounding line to less than 200 m at the ice front. The thickness of Bllenga ice rise varied between 200 and 450 m. The ice shelf thins towards the east, and seems there to flow obliquely to the ice front (Fig.1).Step-like change in thickness of >150 m over 500 m horizontal distance i s observed in the central part of the ice shelf. The records also demonstrate undulations in ice thickness of 600 to 700 m wavelength and 50 m amplitude, and various types of rifts and crevasses. Internal layering is recorded at 250 to 300 m depth over Blåenga and i n the ice shelf up-stream of this ice rise.Observed ice thicknesses on Stancomb-Wills Ice Stream range from 130 to 220 m, with no systematic decrease towards the ice front. The records include long sections of heavy scatter from densely spaced rifts and bottom crevasses. This ice stream attains velocities > 4 km a−1, and is much more active than Riiser-Larsenisen. This high activity has resulted in extensive fracturing of the ice shelf.

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Analysis of ice shelf flexure and its InSAR representation in the grounding zone of the southern McMurdo Ice Shelf

The Cryosphere ◽

10.5194/tc-11-2481-2017 ◽

2017 ◽

Vol 11 (6) ◽

pp. 2481-2490 ◽

Cited By ~ 8

Author(s):

Wolfgang Rack ◽

Matt A. King ◽

Oliver J. Marsh ◽

Christian T. Wild ◽

Dana Floricioiu

Keyword(s):

Vertical Motion ◽

Elastic Beam ◽

Vertical Displacement ◽

Surface Strain ◽

Beam Model ◽

Ice Shelf ◽

Validation Data ◽

Simple Boundary ◽

Grounding Line ◽

Bending Stresses

Abstract. We examine tidal flexure in the grounding zone of the McMurdo Ice Shelf, Antarctica, using a combination of TerraSAR-X repeat-pass radar interferometry, a precise digital elevation model, and GPS ground validation data. Satellite and field data were acquired in tandem between October and December 2014. Our GPS data show a horizontal modulation of up to 60 % of the vertical displacement amplitude at tidal periods within a few kilometres of the grounding line. We ascribe the observed oscillatory horizontal motion to varying bending stresses and account for it using a simple elastic beam model. The horizontal surface strain is removed from nine differential interferograms to obtain precise bending curves. They reveal a fixed (as opposed to tidally migrating) grounding-line position and eliminate the possibility of significant upstream bending at this location. The consequence of apparent vertical motion due to uncorrected horizontal strain in interferometric data is a systematic mislocation of the interferometric grounding line by up to the order of one ice thickness, or several hundred metres. While our field site was selected due to its simple boundary conditions and low background velocity, our findings are relevant to other grounding zones studied by satellite interferometry, particularly studies looking at tidally induced velocity changes or interpreting satellite-based flexure profiles.

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Radio Echo-Sounding of Riiser-Larsenisen (Abstract only)

Annals of Glaciology ◽

10.1017/s0260305500003347 ◽

1982 ◽

Vol 3 ◽

pp. 355 ◽

Cited By ~ 6

Author(s):

Olav Orheim

Keyword(s):

Outer Part ◽

Ice Thickness ◽

Horizontal Distance ◽

Ice Shelf ◽

Ice Stream ◽

Grounding Line ◽

Radio Echo Sounding ◽

Polar Research Institute ◽

Antarctic Research ◽

Echo Sounding

The Norwegian Antarctic Research Expedition 1978–79 used the Scott Polar Research Institute Mk IV radio echo-sounding system fitted in a Bell 206B helicopter to survey 620 km of Riiser-Larsenisen and 100 km across the outer part of Stancomb-Wills Ice Stream. Observed thicknesses of Riiser-Larsenisen decrease from 700 m at the grounding line to less than 200 m at the ice front. The thickness of Bllenga ice rise varied between 200 and 450 m. The ice shelf thins towards the east, and seems there to flow obliquely to the ice front (Fig.1). Step-like change in thickness of >150 m over 500 m horizontal distance i s observed in the central part of the ice shelf. The records also demonstrate undulations in ice thickness of 600 to 700 m wavelength and 50 m amplitude, and various types of rifts and crevasses. Internal layering is recorded at 250 to 300 m depth over Blåenga and i n the ice shelf up-stream of this ice rise. Observed ice thicknesses on Stancomb-Wills Ice Stream range from 130 to 220 m, with no systematic decrease towards the ice front. The records include long sections of heavy scatter from densely spaced rifts and bottom crevasses. This ice stream attains velocities > 4 km a−1, and is much more active than Riiser-Larsenisen. This high activity has resulted in extensive fracturing of the ice shelf.

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Investigations of the mass balance of the southeastern Ronne Ice Shelf, Antarctica

Annals of Glaciology ◽

10.3189/172756499781820996 ◽

1999 ◽

Vol 29 ◽

pp. 250-254 ◽

Cited By ~ 8

Author(s):

A. Lambrecht ◽

C. Mayer ◽

H. Oerter ◽

U. Nixdorf

Keyword(s):

Mass Balance ◽

Mass Flux ◽

Ice Sheet ◽

Ice Thickness ◽

Ice Shelf ◽

Southeastern Part ◽

Ice Stream ◽

Grounding Line ◽

Radio Echo Sounding ◽

Stream Transport

AbstractData from the Filchner V Campaign were used to investigate the mass-balance conditions in the southeastern Ronne Ice Shelf (RIS), Antarctica. Radio-echo sounding and seismic measurements over this area show a maximum ice thickness of >2000 m close to the grounding line of Foundation Ice Stream. The measurements also revealed that the position of this grounding line is 40 km further south than previously thought. New mass-flux calculations result in an estimate of 51 km3 a−1 for the ice-stream transport from the ice sheet into the eastern ice shelf. The Mollereisstrom (MES), west of Foundation Ice Stream, shows a maximum ice thickness of 1100-1200 m in the grounding-line area and a mass flux of 23 km3 a−1.Assuming steady-state conditions, mass-balance calculations based on the new data result in a mean melt rate of about 1 ma−1 at the ice-shelf base for the entire southeastern part of the RIS. The melt rate in the grounding-line area of Foundation Ice Stream exceeds 9 m a−1. In contrast, other ice streams draining into the Filchner-Ronne Ice Shelf show maximum melt rates from 1-2 ma-1. (MES) to 4 ma−1 (Rutford Ice Stream). Our calculations indicate that nearly all of the ice deposited in the drainage area of the eastern RIS on the ice sheet does not reach the ice-shelf front as original meteoric ice, but is melted at the ice-shelf base.

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