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

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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Basal Mass Balance Along a Flow Line on Ronne Ice Shelf, Antarctica (Abstract)

Annals of Glaciology ◽

10.1017/s0260305500006583 ◽

1988 ◽

Vol 11 ◽

pp. 201

Author(s):

A. Jenkins ◽

C.S.M. Doake

Keyword(s):

Steady State ◽

Mass Balance ◽

Flow Line ◽

Average Rate ◽

Ice Shelf ◽

Grounding Line ◽

Radio Echo Sounding ◽

State Models ◽

Basal Melting ◽

Echo Sounding

Recent glaciological work on Ronne Ice Shelf has focused on an assumed flow line which extends from Rutford Ice Stream grounding line to the ice front. Results from doppler satellite surveying and radio echo-sounding are used in kinematic calculations to determine the basal mass balance, assuming the flow line to be in a steady state. Models suggest that basal melting dominates over most of the flow line and is most pronounced at the extremities. In the region within 300 km of the grounding line and over the final 45 km before the ice front, at least 1 m/a on average must melt away to maintain the observed velocity and thickness profile. More gentle melting occurs over about half the remaining distance, but in a region between 130 and 300 km in from the ice front, basal freezing must occur at an average rate of about 0.1 m/a to maintain a steady state. The existence of a thin layer of saline ice underlying the ice shelf, which persists for a further 80 km down-stream before being melted away entirely, is consistent with the weak returns observed during both airborne and ground-based radio echo-sounding in this region.

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

Journal of Glaciology ◽

10.1017/s0022143000042799 ◽

1991 ◽

Vol 37 (125) ◽

pp. 51-58 ◽

Cited By ~ 52

Author(s):

A. M. Smith

Keyword(s):

Elastic Beam ◽

Ice Thickness ◽

Elastic Model ◽

Beam Model ◽

Line Position ◽

Stream Data ◽

Ice Shelf ◽

Ice Stream ◽

Grounding Line ◽

Data Coverage

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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Basal Mass Balance Along a Flow Line on Ronne Ice Shelf, Antarctica (Abstract)

Annals of Glaciology ◽

10.3189/s0260305500006583 ◽

1988 ◽

Vol 11 ◽

pp. 201-201

Author(s):

A. Jenkins ◽

C.S.M. Doake

Keyword(s):

Steady State ◽

Mass Balance ◽

Flow Line ◽

Average Rate ◽

Ice Shelf ◽

Grounding Line ◽

Radio Echo Sounding ◽

State Models ◽

Basal Melting ◽

Echo Sounding

Recent glaciological work on Ronne Ice Shelf has focused on an assumed flow line which extends from Rutford Ice Stream grounding line to the ice front. Results from doppler satellite surveying and radio echo-sounding are used in kinematic calculations to determine the basal mass balance, assuming the flow line to be in a steady state. Models suggest that basal melting dominates over most of the flow line and is most pronounced at the extremities. In the region within 300 km of the grounding line and over the final 45 km before the ice front, at least 1 m/a on average must melt away to maintain the observed velocity and thickness profile. More gentle melting occurs over about half the remaining distance, but in a region between 130 and 300 km in from the ice front, basal freezing must occur at an average rate of about 0.1 m/a to maintain a steady state. The existence of a thin layer of saline ice underlying the ice shelf, which persists for a further 80 km down-stream before being melted away entirely, is consistent with the weak returns observed during both airborne and ground-based radio echo-sounding in this region.

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

Journal of Glaciology ◽

10.3189/s0022143000042799 ◽

1991 ◽

Vol 37 (125) ◽

pp. 51-58 ◽

Cited By ~ 3

Author(s):

A. M. Smith

Keyword(s):

Elastic Beam ◽

Ice Thickness ◽

Elastic Model ◽

Beam Model ◽

Line Position ◽

Stream Data ◽

Ice Shelf ◽

Ice Stream ◽

Grounding Line ◽

Data Coverage

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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Surface elevation, ice thickness, and subglacial-bedrock topography of Ekström Ice Shelf (Antarctica) and its catchment area

Annals of Glaciology ◽

10.3189/172756400781820723 ◽

2000 ◽

Vol 30 ◽

pp. 61-68 ◽

Cited By ~ 3

Author(s):

H. Sandhäger ◽

N. Blindow

Keyword(s):

Catchment Area ◽

Drainage System ◽

Ice Thickness ◽

Ice Shelf ◽

Bedrock Topography ◽

Ice Surface ◽

Catchment Areas ◽

Grounding Line ◽

Radio Echo Sounding ◽

Mass Discharge

AbstractEkström Ice Shelf and its catchment area form a comparatively small (∼29 000 km2) drainage system in northern Dronning Maud Land, Antarctica. Aerial-altimetry and radio-echo-sounding data of this region have been used to derive detailed maps of ice-surface and bedrock topographies and ice thickness. With the new database the volumes of the floating and grounded ice in the drainage system are calculated to be ∼3200 km3 and ∼16 000 km3, respectively. This corresponds to a total ice mass of ∼17 000 Gt. Four significant graben-like depressions in the bedrock topography have been identified, which incline from inland towards the grounding line and are up to ∼16 km wide there. These structures coincide with the particular zones of concentrated ice flux into the ice shelf. The total mean annual mass discharge over the grounding line of the larger western part and the smaller eastern part of Ekström Ice Shelf is estimated to be about 3.7 Gt and 0.4 Gt, respectively. Both parts represent individual ice-shelf systems with different catchment areas, geometric characteristics and flow regimes.

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Absolute Movements, Mass Balance, and Snow Temperatures of the Riiser-Larsenisen (Abstract only)

Annals of Glaciology ◽

10.1017/s0260305500003177 ◽

1982 ◽

Vol 3 ◽

pp. 346 ◽

Cited By ~ 1

Author(s):

Yngvar Gjessing ◽

Bjørn Wold

Keyword(s):

Mass Balance ◽

Air Temperature ◽

Outer Part ◽

Temperature Inversion ◽

Atmospheric Temperature ◽

Snow Accumulation ◽

Ice Shelf ◽

Grounding Line ◽

Dronning Maud Land ◽

Antarctic Research

During the Norwegian Antarctic Research Expeditions 1967–77 and 1978–79 a land party worked on Riiser-Larsenisen, an ice shelf 120 km wide on the coast of Dronning Maud Land (15° to 20°W). In February 1977 three patterns of six stakes each were laid out over areas of about 4 km2 as part of a combined investigation into absolute movements and strain-rates. Eight stakes for absolute movement were also laid out. The stakes were also used for determination of mean snow accumulation together with a stake line across the ice shelf. The positions of the stakes were determined by theodolite observations from the stake points and from trigonometric stations located on land and on an ice rise near the ice front. In February 1979 all these measurements were repeated, and absolute movement, deformation, and mean accumulation were calculated. The absolute velocity of the ice shelf varied from 30 m a−1 near the grounding line to 130 m a−1 near the ice front. The mean annual accumulation was 510 mm water equivalent on the outer part of the ice shelf and 580 mm at the grounding line. Based on these measurements, together with snow-density measurements down to 16 m and measurements of the height of the ice shelf, the mass balance of the ice shelf was studied. The stake pattern across the grounding line showed considerable expansion. This is interpreted as a result of water freezing in bottom crevasses made by the tides. In 1979 snow temperatures were measured in eight bore holes down to 10 m depth. The snow temperatures at 10 m depth were used as a measure of the annual mean air temperature. The annual mean air temperature ranged from -16.8°C near the ice front to -19.2°C at the grounding line. Snow temperatures in bore holes on the slope of the ice rise and inland indicate a mean atmospheric temperature inversion of 0.28°C 100 m−1 for a 440 m layer near the grounding line, and 0.30°C 100 m−1 for a 160 m layer near the ice front. Here a mean inversion of 2.8°C 100 m−1 was found for the lowest 40 m layer of the atmosphere.

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The role of ice thickness and bed properties on the dynamics of the enhanced-flow tributaries of Bailey Ice Stream and Slessor Glacier, East Antarctica

Annals of Glaciology ◽

10.3189/172756404781814375 ◽

2004 ◽

Vol 39 ◽

pp. 366-372 ◽

Cited By ~ 15

Author(s):

David M. Rippin ◽

Jonathan L. Bamber ◽

Martin J. Siegert ◽

David G. Vaughan ◽

Hugh F. J. Corr

Keyword(s):

Numerical Modelling ◽

Significant Proportion ◽

East Antarctica ◽

Ice Thickness ◽

Ice Stream ◽

Radio Echo Sounding ◽

Basal Reflection ◽

Echo Sounding ◽

Modelling Study

AbstractAirborne radio-echo sounding investigations in the upper reaches of Bailey Ice Stream and Slessor Glacier, Coats Land, East Antarctica, have shown that enhanced-flow tributaries are associated with well-defined areas of relatively thicker ice, and are separated from each other by areas of relatively thinner ice. A numerical modelling study has revealed that while internal ice deformation might account for all the observed flow in inter-tributary areas and the majority in the Slessor tributaries, a significant proportion of the flow of Bailey tributary is attributable to basal motion. Further, investigations of depth-corrected basal reflection power indicate that the bed underlying both Bailey and Slessor enhanced-flow tributaries is significantly smoother than in the slower-moving inter-tributary areas. It is thus proposed that enhanced motion within Bailey tributary (and also perhaps Slessor) may be facilitated by a reduction in basal roughness, caused by the accumulation of water and/or sediments within subglacial valleys, or by the erosion and smoothing of bed obstacles.

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