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

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

Journal of Glaciology ◽

10.3189/002214389793701545 ◽

1989 ◽

Vol 35 (119) ◽

pp. 38-42 ◽

Cited By ~ 12

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.

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The Equilibrium State of the Eastern Half of the Ross Ice Shelf

Journal of Glaciology ◽

10.3189/s0022143000020906 ◽

1978 ◽

Vol 20 (84) ◽

pp. 509-518 ◽

Cited By ~ 1

Author(s):

Robert H. Thomas ◽

Charles R. Bentley

Keyword(s):

Indirect Evidence ◽

Melting Rate ◽

Snow Accumulation ◽

Surface Strain ◽

The South ◽

Ice Shelf ◽

Ross Ice Shelf ◽

Average Value ◽

West Antarctic ◽

Flow Band

AbstractMeasurements of ice thickness, velocity, snow accumulation rates, and surface strain-rates are used to examine the state of equilibrium of three flow bands of the Ross Ice Shelf. The analysis gives the rate of thickening of the ice shelf in terms of the basal freezing rate, which is unknown. However, indirect evidence suggests that the basal flux ranges from a small value of freezing in the south to a melting rate of about one meter of ice per year at the ice front. If these values are correct then the flow band in the south-east corner of the ice shelf appears to be thickening at an average value of (34 ± 15) cm of ice per year. Persistent thickening at this rate must lead to grounding of large areas of the ice shelf. This would restrict drainage from West Antarctic ice streams which feed this part of the ice shelf and these would tend to thicken and advance their grounding lines into the ice shelf. Further north, near the RISP bore-hole site, the ice shelf is probably in equilibrium. The largest flow band is to the south and east of Roosevelt Island, and this also may be in equilibrium if there is significant bottom melting from ice shelf that is more than 100 km from the ice front.

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

Annals of Glaciology ◽

10.3189/s0260305500006364 ◽

1988 ◽

Vol 11 ◽

pp. 77-82 ◽

Cited By ~ 3

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.

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The Equilibrium State of the Eastern Half of the Ross Ice Shelf

Journal of Glaciology ◽

10.1017/s0022143000020906 ◽

1978 ◽

Vol 20 (84) ◽

pp. 509-518 ◽

Cited By ~ 51

Author(s):

Robert H. Thomas ◽

Charles R. Bentley

Keyword(s):

Indirect Evidence ◽

Melting Rate ◽

Snow Accumulation ◽

Surface Strain ◽

The South ◽

Ice Shelf ◽

Ross Ice Shelf ◽

Average Value ◽

West Antarctic ◽

Flow Band

AbstractMeasurements of ice thickness, velocity, snow accumulation rates, and surface strain-rates are used to examine the state of equilibrium of three flow bands of the Ross Ice Shelf. The analysis gives the rate of thickening of the ice shelf in terms of the basal freezing rate, which is unknown. However, indirect evidence suggests that the basal flux ranges from a small value of freezing in the south to a melting rate of about one meter of ice per year at the ice front. If these values are correct then the flow band in the south-east corner of the ice shelf appears to be thickening at an average value of (34 ± 15) cm of ice per year. Persistent thickening at this rate must lead to grounding of large areas of the ice shelf. This would restrict drainage from West Antarctic ice streams which feed this part of the ice shelf and these would tend to thicken and advance their grounding lines into the ice shelf. Further north, near the RISP bore-hole site, the ice shelf is probably in equilibrium. The largest flow band is to the south and east of Roosevelt Island, and this also may be in equilibrium if there is significant bottom melting from ice shelf that is more than 100 km from the ice front.

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Strong tidal variations in ice flow observed across the entire Ronne Ice Shelf and adjoining ice streams

Earth System Science Data ◽

10.5194/essd-9-849-2017 ◽

2017 ◽

Vol 9 (2) ◽

pp. 849-860 ◽

Cited By ~ 3

Author(s):

Sebastian H. R. Rosier ◽

G. Hilmar Gudmundsson ◽

Matt A. King ◽

Keith W. Nicholls ◽

Keith Makinson ◽

...

Keyword(s):

Surface Flow ◽

Decay Length ◽

Mean Flow ◽

Ice Shelf ◽

Ice Streams ◽

Data Set ◽

Ice Flow ◽

Ice Stream ◽

Flow Speeds ◽

Tidal Variations

Abstract. We present a compilation of GPS time series, including those for previously unpublished sites, showing that flow across the entire Ronne Ice Shelf and its adjoining ice streams is strongly affected by ocean tides. Previous observations have shown strong horizontal diurnal and semidiurnal motion of the ice shelf, and surface flow speeds of Rutford Ice Stream (RIS) are known to vary with a fortnightly (Msf) periodicity. Our new data set shows that the Msf flow modulation, first observed on RIS, is also found on Evans, Talutis, Institute, and Foundation ice streams, i.e. on all ice streams for which data are available. The amplitude of the Msf signal increases downstream of grounding lines, reaching up to 20 % of mean flow speeds where ice streams feed into the main ice shelf. Upstream of ice stream grounding lines, decay length scales are relatively uniform for all ice streams but the speed at which the Msf signal propagates upstream shows more variation. Observations and modelling of tidal variations in ice flow can help constrain crucial parameters that determine the rate and extent of potential ice mass loss from Antarctica. Given that the Msf modulation in ice flow is readily observed across the entire region at distances of up to 80 km upstream of grounding lines, but is not completely reproduced in any existing numerical model, this new data set suggests a pressing need to identify the missing processes responsible for its generation and propagation. The new GPS data set is publicly available through the UK Polar Data Centre at http://doi.org/10.5285/4fe11286-0e53-4a03-854c-a79a44d1e356.

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

The Cryosphere Discussions ◽

10.5194/tcd-8-2043-2014 ◽

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.

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Grounding-zone flow variability of Priestley Glacier, Antarctica, in a diurnal tidal regime

10.5194/egusphere-egu21-15197 ◽

2021 ◽

Author(s):

Reinhard Drews ◽

Christian Wild ◽

Oliver Marsh ◽

Wolfgang Rack ◽

Todd Ehlers ◽

...

Keyword(s):

Spatial Scales ◽

Ice Shelf ◽

Ice Streams ◽

Ice Flow ◽

Ice Shelves ◽

Ice Stream ◽

Grounding Line ◽

Temporal And Spatial ◽

Gnss Measurements ◽

Natural Laboratory

<p>Dynamics of polar outlet glaciers vary with ocean tides, providing a natural laboratory to understand basal processes beneath ice streams, ice rheology and ice-shelf buttressing. We apply Terrestrial Radar Interferometry to close the spatiotemporal gap between localized, temporally well-resolved GNSS and area-wide but sparse satellite observations. Three-hour flowfields collected over an eight day period at Priestley Glacier, Antarctica, validate and provide the spatial context for concurrent GNSS measurements. Ice flow is fastest during falling tides and slowest during rising tides. Principal components of the timeseries prove upstream propagation of tidal signatures $>$ 10 km away from the grounding line. Hourly, cm-scale horizontal and vertical flexure patterns occur $>$6 km upstream of the grounding line. Vertical uplift upstream of the grounding line is consistent with ephemeral re-grounding during low-tide impacting grounding-zone stability. On the freely floating ice shelves, we find velocity peaks both during high- and low-tide suggesting that ice-shelf buttressing varies temporally as a function of flexural bending from tidal displacement. Taken together, these observations identify tidal imprints on ice-stream dynamics on new temporal and spatial scales providing constraints for models designed to isolate dominating processes in ice-stream and ice-shelf mechanics.</p>

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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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Surface velocity and mass balance of Ice Streams D and E, West Antarctica

Journal of Glaciology ◽

10.3189/s0022143000003452 ◽

1996 ◽

Vol 42 (142) ◽

pp. 461-475 ◽

Cited By ~ 4

Author(s):

Robert Bindschadler ◽

Patricia Vornberger ◽

Donald Blankenship ◽

Ted Scambos ◽

Robert Jacobel

Keyword(s):

Mass Balance ◽

Surface Velocity ◽

Random Errors ◽

West Antarctica ◽

Velocity Measurements ◽

Ice Streams ◽

Ice Stream ◽

Data Density ◽

Basal Shear ◽

Collection Methods

AbstractOver 75 000 surface-velocity measurements are extracted from sequential satellite imagery of Ice Streams D and E to reveal a complex pattern of flow not apparent from previous measurements. Horizontal and vertical strain rates, calculated from surface velocity, indicate that the bed experiences larger basal shear where the surface of these ice streams is rougher. Ten airborne-radar profiles and one surface-based radar profile of ice thickness make possible the calculation of mass balance for longitudinal sections of each ice stream. Improved data-collection methods increase data density, substantially reducing random errors in velocity. However, systematic errors continue to limit the ability of the flux-differencing technique used here to resolve local variations in mass balance. Nevertheless, significant local variations in mass balance are revealed, while, overall, Ice Streams D and E are in approximate equilibrium. An earlier estimate of the net mass balance for Ice Stream D is improved.

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