scholarly journals Ice-Shelf Response to Ice-stream Discharge Fluctuations: III. The Effects of Ice-stream Imbalance on the Ross Ice Shelf, Antarctica

1989 ◽  
Vol 35 (119) ◽  
pp. 38-42 ◽  
Author(s):  
Douglas R. Macayeal
Keyword(s):  
Snow Accumulation ◽  
Time Span ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ross Ice Shelf ◽  
Stream Discharge ◽  
Ice Stream ◽  
Discharge Rates ◽  
Short Time Span ◽  
Catchment Areas

AbstractA numerical simulation of the Ross Ice Shelf, Antarctica, in which discharge from Ice Streams A-E is changed suddenly between extreme states, is used to investigate ice-shelf thickness and flow anomalies generated by ice-stream transience. At one extreme, ice-stream discharge rates specified as model boundary conditions are balanced individually with snow accumulation in the ice-stream catchment areas. At the other, discharge rates are fixed at current observed values which widely depart from mass balance. The simulated ice-shelf evolution between initial and final steady states suggests that ice-thickness and velocity fields adjust to new ice-stream conditions over a relatively short time span (approximately 500 years). In contrast, transitory geometrics of medial moraines and relict-crevasse bands persist over a longer time span (up to 2000 years). Contortions of medial moraines and relict-crevasse bands thus may provide a useful long-term history of past ice-stream activity. The past stoppage of Ice Stream C, for example, should be evident today in some medial moraine trajectories even if the stoppage occurred over 1000 years ago. Ice-shelf thickness fluctuations induced by ice-stream activity are generally restricted to the neighborhood of the grounding line. These fluctuations may constitute a trigger for ice-rise formation near ice-stream outlets.

scholarly journals A millennium of variable ice flow recorded by the Ross Ice Shelf, Antarctica

2000 ◽  
Vol 46 (155) ◽  
pp. 652-664 ◽  
Author(s):  
M. A. Fahnestock ◽  
T. A. Scambos ◽  
R. A. Bindschadler ◽  
G. Kvaran
Keyword(s):  
Landsat Imagery ◽  
Ice Shelf ◽  
Ice Streams ◽  
The West ◽  
Northern Margin ◽  
Ross Ice Shelf ◽  
Stream Discharge ◽  
Ice Stream ◽  
History Of ◽  
Ice Stream B

AbstractAn enhanced composite Advanced Very High Resolution Radiometer (AVHRR) image is used to map flow stripes and rifts across the Ross Ice Shelf, Antarctica. The patterns of these flow-related features reveal a history of discharge variations from the ice streams feeding the eastern part of the shelf. The most profound variations are visible in the track of rifts downstream of Crary Ice Rise, flow-stripe bends to the west of this ice rise and adjacent to Steershead ice rise, and changes in the northern margin of Ice Stream B. The track of rifts downstream of Crary Ice Rise indicates that the ice rise has existed for at least 700 years. The character of this track changes about 350 km downstream, indicating a rearrangement of flow patterns about 550 years ago. The large bulge in the flow stripes to the west of Crary Ice Rise is shown in detail, with bent flow stripes extending for several hundred kilometers along flow; this feature formed from the south, possibly due to a change in the discharge of Ice Stream A. The AVHRR image documents a complex history associated with the shutdown of Ice Stream C, with changes in the margins of Ice Stream C and the northern margin of Ice Stream B, and the grounding of Steershead ice rise with an associated bending and truncation of flow stripes. Landsat imagery shows a region that appears to be actively extending just downstream of the ice rise, as the shelf continues to respond to recent changes in ice-stream discharge. We present a four-stage flow history which accounts for the features preserved in the ice shelf.

scholarly journals Twelve years of ice velocity change in Antarctica observed by RADARSAT-1 and -2 satellite radar interferometry

2012 ◽  
Vol 6 (3) ◽  
pp. 1715-1738 ◽  
Author(s):  
B. Scheuchl ◽  
J. Mouginot ◽  
E. Rignot
Keyword(s):  
Ice Shelf ◽  
Ice Streams ◽  
Velocity Difference ◽  
Velocity Change ◽  
Ice Dynamics ◽  
Ice Shelves ◽  
Ross Ice Shelf ◽  
Ice Stream ◽  
Catchment Areas ◽  
Ice Velocity

Abstract. We report changes in ice velocity of a 6.5 million km2 region around South Pole encompassing the Ronne/Filchner and Ross Ice Shelves and a significant portion of the ice streams and glaciers that constitute their catchment areas. Using the first full interferometric synthetic-aperture radar (InSAR) coverage of the region completed in 2009 and partial coverage acquired in 1997, we process the data to assemble a comprehensive map of ice velocity changes with a nominal precision of detection of ±3–4 m yr–1. The largest observed changes, an increase in speed of 100 m yr–1 in 12 yr, are near the frontal regions of the large ice shelves and are associated with the slow detachment of large tabular blocks that will eventually form icebergs. On the Ross Ice Shelf, our data reveal a slow down of Mercer and Whillans Ice Streams with a 12 yr velocity difference of 50 m yr–1 (16.7 %) and 100 m yr–1 (25.3 %) at their grounding lines. The slow down spreads 450 km upstream of the grounding line and more than 500 km onto the shelf, i.e., far beyond what was previously known. Also slowing in the Ross Ice Shelf sector are MacAyeal Ice Stream and Byrd Glacier with a 12 yr velocity difference near their grounding lines of 30 m yr–1 (6.7 %) and 35 m yr–1 (4.1 %), respectively. Bindschadler Ice Stream is faster by 20 m yr–1 (5 %). Most of these changes in glacier speed extend on the Ross Ice Shelf along the ice streams' flow lines. At the mouth of the Filchner/Ronne Ice Shelves, the 12 yr difference in glacier speed is below the 8 % level. We detect the largest slow down with a 12 yr velocity difference of up to 30 m yr–1 on Slessor and Recovery Glaciers, equivalent to 6.7 % and 3.3 %, respectively. Foundation Ice Stream shows a modest speed up (30 m yr–1 or 5 %). No change is detected on Bailey, Rutford, and Institute Ice Streams. On the Filchner Ice Shelf proper, ice slowed down rather uniformly with a 12 yr velocity difference of 50 m yr–1, or 5 % of its ice front speed, which we attribute to an 12 km advance in its ice front position. Overall, we conclude that the ice streams and ice shelves in this broad region, in contrast with their counterparts in the Amundsen and Bellingshausen seas, exhibit changes in ice dynamics that have almost no impact on the overall ice balance of the region.

scholarly journals Can Relict Crevasse Plumes on Antarctic Ice Shelves Reveal a History of Ice-Stream Fluctuation?

1988 ◽  
Vol 11 ◽  
pp. 77-82 ◽  
Author(s):  
D. R. MacAyeal ◽  
R. A. Bindschadler ◽  
K. C. Jezek ◽  
S. Shabtaie
Keyword(s):  
Numerical Model ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Shelves ◽  
Stream Discharge ◽  
Ice Stream ◽  
History Of

Configurations of relict surface-crevasse bands and medial moraines that emanate from the shear margins of ice streams are simulated, using a numerical model of an ideal rectangular ice shelf to determine their potential for recording a past ice-stream discharge chronology.

scholarly journals Force, Mass, and Energy Budgets of the Crary Ice Rise Complex, Antarctica

1987 ◽  
Vol 33 (114) ◽  
pp. 218-230 ◽  
Author(s):  
D.R. Macayeal ◽  
R.A. Bindschadler ◽  
S. Shabtaie ◽  
S. Stephenson ◽  
C.R. Bentley
Keyword(s):  
Potential Energy ◽  
Snow Accumulation ◽  
Back Pressure ◽  
Surface Strain ◽  
Surface Velocity ◽  
Pressure Force ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Stream ◽  
Work Done

AbstractResistive force exerted by the Crary Ice Rise on its ice-shelf/ice-stream environment and back-pressure force transmitted across the grounding lines of Ice Streams A and B are calculated from airborne radio echo-sounding data and measurements of surface strain-rates. Resistance generated by the ice rise ranges in magnitude between 45 and 51% of the back-pressure force on the ice streams (depending on the flow law). The mechanical-energy budget of the ice rise is computed by considering work done against frictional forces at the perimeter of the ice rise and gravitational potential energy fluxes associated with changing mass distribution in the ice/ocean system. Energy dissipated by flow surrounding the ice rise is balanced by potential energy released within Ice Streams A and B, and accounts for between 15 and 49% of the work done by the ice streams against ice-shelf back pressure at their grounding lines. Mass balance of the ice rise, and the discharge of Ice Streams A and B, are calculated from surface-velocity and snow-accumulation measurements. The ice rise and its immediate environment gain mass by advection and snowfall at a rate equivalent to an area-averaged thickening rate of 0.44 ± 0.06 m/year. This mass gain may be balanced by regional basal melting (which we do not measure), or could contribute to ice-rise expansion through regional thickening and ice-shelf grounding. Approximately 1/4 to 1/2 of the excess volume discharged by Ice Streams A and B above snow accumulation in their catchment areas is deposited in the vicinity of the ice rise (or melted from the bottom of the ice shelf). This suggests that the ice rise may have formed as a consequence of recent ice-stream acceleration, and that its continued growth may eventually reverse this trend of ice-stream discharge.

scholarly journals Quantifying the Jakobshavn Effect: Jakobshavn Isbrae, Greenland, compared to Byrd Glacier, Antarctica

2014 ◽  
Vol 8 (2) ◽  
pp. 2043-2118
Author(s):  
T. Hughes ◽  
A. Sargent ◽  
J. Fastook ◽  
K. Purdon ◽  
J. Li ◽  
...  
Keyword(s):  
Ice Sheets ◽  
Greenland Ice Sheet ◽  
Force Balance ◽  
Ice Age ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ross Ice Shelf ◽  
Ice Stream ◽  
Visual Understanding ◽  
Subglacial Lakes

Abstract. The Jakobshavn Effect is a series of positive feedback mechanisms that was first observed on Jakobshavn Isbrae, which drains the west-central part of the Greenland Ice Sheet and enters Jakobshavn Isfjord at 69°10'. These mechanisms fall into two categories, reductions of ice-bed coupling beneath an ice stream due to surface meltwater reaching the bed, and reductions in ice-shelf buttressing beyond an ice stream due to disintegration of a laterally confined and locally pinned ice shelf. These uncoupling and unbuttressing mechanisms have recently taken place for Byrd Glacier in Antarctica and Jakobshavn Isbrae in Greenland, respectively. For Byrd Glacier, no surface meltwater reaches the bed. That water is supplied by drainage of two large subglacial lakes where East Antarctic ice converges strongly on Byrd Glacier. Results from modeling both mechanisms are presented here. We find that the Jakobshavn Effect is not active for Byrd Glacier, but is active for Jakobshavn Isbrae, at least for now. Our treatment is holistic in the sense it provides continuity from sheet flow to stream flow to shelf flow. It relies primarily on a force balance, so our results cannot be used to predict long-term behavior of these ice streams. The treatment uses geometrical representations of gravitational and resisting forces that provide a visual understanding of these forces, without involving partial differential equations and continuum mechanics. The Jakobshavn Effect was proposed to facilitate terminations of glaciation cycles during the Quaternary Ice Age by collapsing marine parts of ice sheets. This is unlikely for the Antarctic and Greenland ice sheets, based on our results for Byrd Glacier and Jakobshavn Isbrae, without drastic climate warming in high polar latitudes. Warming would affect other Antarctic ice streams already weakly buttressed or unbuttressed by an ice shelf. Ross Ice Shelf would still protect Byrd Glacier.

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

1988 ◽  
Vol 11 ◽  
pp. 165-172 ◽  
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.

scholarly journals Timing of stagnation of Ice Stream C, West Antarctica, from short-pulse radar studies of buried surface crevasses

1993 ◽  
Vol 39 (133) ◽  
pp. 553-561 ◽  
Author(s):  
Rory Retzlaff ◽  
Charles R. Bentley
Keyword(s):  
Short Pulse ◽  
Water Pressure ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ross Ice Shelf ◽  
Pulse Radar ◽  
West Antarctic ◽  
Ice Stream ◽  
Inland Ice

AbstractFive short-pulse radar profiles were run across the edge of inactive Ice Stream C, one of the “Ross” ice streams that flows from the West Antarctic inland ice sheet into the Ross Ice Shelf. Scatter from buried crevasses, which we presume were at the surface of the ice stream when it was active, creates hyperbolae on the radar records. A density-depth curve and local accumulation rates were used to convert the picked travel times of the apices of the hyperbolae into stagnation ages for the ice stream. Stagnation ages are 130 ± 25 year for the three profiles farthest downstream and marginally less (100 ± 30 year) for the fourth. The profile farthest upstream shows a stagnation age of only ~30 year. We believe that these results indicate a “wave” of stagnation propagating at a diminishing speed upstream from the mouth of the ice stream, and we suggest that the stagnation process involves a drop in water pressure at the bed due to a conversion from sheet flow to channelized water flow.

scholarly journals Active subglacial lakes and channelized water flow beneath the Kamb Ice Stream

2016 ◽  
Vol 10 (6) ◽  
pp. 2971-2980 ◽  
Author(s):  
Byeong-Hoon Kim ◽  
Choon-Ki Lee ◽  
Ki-Weon Seo ◽  
Won Sang Lee ◽  
Ted Scambos
Keyword(s):  
Water System ◽  
Topographic Feature ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ross Ice Shelf ◽  
Subglacial Lake ◽  
Ice Stream ◽  
Grounding Line ◽  
Subglacial Lakes ◽  
Kamb Ice Stream

Abstract. We identify two previously unknown subglacial lakes beneath the stagnated trunk of the Kamb Ice Stream (KIS). Rapid fill-drain hydrologic events over several months are inferred from surface height changes measured by CryoSat-2 altimetry and indicate that the lakes are probably connected by a subglacial drainage network, whose structure is inferred from the regional hydraulic potential and probably links the lakes. The sequential fill-drain behavior of the subglacial lakes and concurrent rapid thinning in a channel-like topographic feature near the grounding line implies that the subglacial water repeatedly flows from the region above the trunk to the KIS grounding line and out beneath the Ross Ice Shelf. Ice shelf elevation near the hypothesized outlet is observed to decrease slowly during the study period. Our finding supports a previously published conceptual model of the KIS shutdown stemming from a transition from distributed flow to well-drained channelized flow of subglacial water. However, a water-piracy hypothesis in which the KIS subglacial water system is being starved by drainage in adjacent ice streams is also supported by the fact that the degree of KIS trunk subglacial lake activity is relatively weaker than those of the upstream lakes.

scholarly journals Can Relict Crevasse Plumes on Antarctic Ice Shelves Reveal a History of Ice-Stream Fluctuation?

1988 ◽  
Vol 11 ◽  
pp. 77-82 ◽  
Author(s):  
D. R. MacAyeal ◽  
R. A. Bindschadler ◽  
K. C. Jezek ◽  
S. Shabtaie
Keyword(s):  
Numerical Model ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Shelves ◽  
Stream Discharge ◽  
Ice Stream ◽  
History Of

Configurations of relict surface-crevasse bands and medial moraines that emanate from the shear margins of ice streams are simulated, using a numerical model of an ideal rectangular ice shelf to determine their potential for recording a past ice-stream discharge chronology.

scholarly journals Force, Mass, and Energy Budgets of the Crary Ice Rise Complex, Antarctica

1987 ◽  
Vol 33 (114) ◽  
pp. 218-230 ◽  
Author(s):  
D.R. Macayeal ◽  
R.A. Bindschadler ◽  
S. Shabtaie ◽  
S. Stephenson ◽  
C.R. Bentley
Keyword(s):  
Potential Energy ◽  
Snow Accumulation ◽  
Back Pressure ◽  
Surface Strain ◽  
Surface Velocity ◽  
Pressure Force ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Stream ◽  
Work Done

AbstractResistive force exerted by the Crary Ice Rise on its ice-shelf/ice-stream environment and back-pressure force transmitted across the grounding lines of Ice Streams A and B are calculated from airborne radio echo-sounding data and measurements of surface strain-rates. Resistance generated by the ice rise ranges in magnitude between 45 and 51% of the back-pressure force on the ice streams (depending on the flow law). The mechanical-energy budget of the ice rise is computed by considering work done against frictional forces at the perimeter of the ice rise and gravitational potential energy fluxes associated with changing mass distribution in the ice/ocean system. Energy dissipated by flow surrounding the ice rise is balanced by potential energy released within Ice Streams A and B, and accounts for between 15 and 49% of the work done by the ice streams against ice-shelf back pressure at their grounding lines. Mass balance of the ice rise, and the discharge of Ice Streams A and B, are calculated from surface-velocity and snow-accumulation measurements. The ice rise and its immediate environment gain mass by advection and snowfall at a rate equivalent to an area-averaged thickening rate of 0.44 ± 0.06 m/year. This mass gain may be balanced by regional basal melting (which we do not measure), or could contribute to ice-rise expansion through regional thickening and ice-shelf grounding. Approximately 1/4 to 1/2 of the excess volume discharged by Ice Streams A and B above snow accumulation in their catchment areas is deposited in the vicinity of the ice rise (or melted from the bottom of the ice shelf). This suggests that the ice rise may have formed as a consequence of recent ice-stream acceleration, and that its continued growth may eventually reverse this trend of ice-stream discharge.

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