Estimation of ice fabric within Whillans Ice Stream using polarimetric phase-sensitive radar sounding

AbstractHere we use polarimetric measurements from an Autonomous phase-sensitive Radio-Echo Sounder (ApRES) to investigate ice fabric within Whillans Ice Stream, West Antarctica. The survey traverse is bounded at one end by the suture zone with the Mercer Ice Stream and at the other end by a basal ‘sticky spot’. Our data analysis employs a phase-based polarimetric coherence method to estimate horizontal ice fabric properties: the fabric orientation and the magnitude of the horizontal fabric asymmetry. We infer an azimuthal rotation in the prevailing horizontal c-axis between the near-surface (z ≈ 10–50 m) and deeper ice (z ≈ 170–360 m), with the near-surface orientated closer to perpendicular to flow and deeper ice closer to parallel. In the near-surface, the fabric asymmetry increases toward the center of Whillans Ice Stream which is consistent with the surface compression direction. By contrast, the fabric orientation in deeper ice is not aligned with the surface compression direction but is consistent with englacial ice reacting to longitudinal compression associated with basal resistance from the nearby sticky spot.

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Basal melt rates beneath Whillans Ice Stream, West Antarctica

Journal of Glaciology ◽

10.3189/002214310793146241 ◽

2010 ◽

Vol 56 (198) ◽

pp. 647-654 ◽

Cited By ~ 21

Author(s):

Lucas H. Beem ◽

Ken C. Jezek ◽

C.J. Van Der Veen

Keyword(s):

West Antarctica ◽

Ice Streams ◽

Stress Regime ◽

Basal Resistance ◽

West Antarctic ◽

Ice Stream ◽

Whillans Ice Stream ◽

Fast Flow ◽

Insight Into ◽

Streaming Flow

AbstractBasal water lubricates and enables the fast flow of the West Antarctic ice streams which exist under low gravitational driving stress. Identification of sources and rates of basal meltwater production can provide insight into the dynamics of ice streams and the subglacial hydrology, which remain insufficiently described by glaciological theory. Combining measurements and analytic modeling, we identify two regions where basal meltwater is produced beneath Whillans Ice Stream, West Antarctica. Downstream of the onset of shear crevasses, strong basal melt (20–50 mm a−1) is concentrated beneath the relatively narrow shear margins. Farther upstream, melt rates are consistently 3–7 mm a−1 across the width of the ice stream. We show that the transition in melt-rate patterns is coincident with the onset of shear margin crevassing and streaming flow and related to the development of significant lateral shear resistance, which reorganizes the resistive stress regime and induces a concentration of basal resistance adjacent to the shear margin. Finally, we discuss how downstream freeze-on in the ice-stream center coupled with melt beneath the shear margin might result in a slowing but widening ice stream.

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Bed radar reflectivity across the north margin of Whillans Ice Stream, West Antarctica, and implications for margin processes

Journal of Glaciology ◽

10.3189/172756506781828890 ◽

2006 ◽

Vol 52 (176) ◽

pp. 3-10 ◽

Cited By ~ 25

Author(s):

C.F. Raymond ◽

Ginny A. Catania ◽

Nadine Nereson ◽

C.J. Van Der Veen

Keyword(s):

Low Frequency ◽

Radar Signal ◽

Surface Zone ◽

Internal Layers ◽

West Antarctica ◽

Near Surface ◽

Ice Stream ◽

Whillans Ice Stream ◽

Slow Moving ◽

Fast Motion

AbstractSurface-based ice-penetrating radar profiles were made across the active north margin (the Snake) of the upper part of Whillans Ice Stream (formerly Ice Stream B, branch B2), West Antarctica, at three locations. Low frequency (about 2 MHz) and the ground deployment of the radar allowed penetration through the near-surface zone of fracturing to detect internal layering and bed reflection characteristics on continuous profiles spanning from the slow-moving ice of Engelhardt Ridge well into the chaotic zone of the shear margin. Internal layers were tracked beneath the chaotic zone, where they are warped but remain continuous. The energy returned from internal layers showed no systematic changes associated with the transition from the undisturbed surface of the slow-moving ice into the fractured surface of the shear margin, thus indicating little effect from the surface crevasses on the penetration of the radar signal. Based on this calibration of the near-surface effects and corrections for path length, spreading and attenuation, we examine the spatial variation of bed reflectivity. Low bed reflectivity found under Engelhardt Ridge extends under the chaotic zone of the margin into fast-moving ice. We argue that the fast motion in a band along the margin is mediated by processes other than deformation of thick dilated till that is the source of lubrication allowing fast motion in the interior of the ice stream.

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Numerical investigations of the slow-down of Whillans Ice Stream, West Antarctica: is it shutting down like Ice Stream C?

Annals of Glaciology ◽

10.3189/172756403781815555 ◽

2003 ◽

Vol 37 ◽

pp. 239-246 ◽

Cited By ~ 36

Author(s):

Marion Bougamont ◽

Slawek Tulaczyk ◽

Ian Joughin

Keyword(s):

Stream Water ◽

Drainage System ◽

Water Drainage ◽

West Antarctica ◽

Basal Resistance ◽

Ice Stream ◽

Whillans Ice Stream ◽

Out Of Plane ◽

Basal Melting ◽

Near Future

AbstractWe investigate whether the recent slow-down of Whillans Ice Stream (WIS), West Antarctica, may lead to its complete stoppage in the near future, using a numerical model. Basal resistance to ice-stream motion is represented by a continuous till layer whose strength changes in response to basal melting and freezing. We implement a basal drainage system, which acts to hinder ice-stream stoppage through supply of extra water to those parts of the bed that are experiencing freezing. The ice module is a standard flowline model with parameterized key out-of-plane effects (Raymond, 1996). The most important result of our modeling effort is that we never obtained a slow-down that would not be followed by a complete stoppage within <100 years. WIS slow-down can be avoided in the model if large basal water-input rates are assumed, to satisfy basal freezing. In comparison, the tested perturbations in WIS width and mass balance had a relatively small effect on the tendency of the simulated ice stream to slow down. These results underscore the need for more quantitative constraints on the efficiency of sub-ice-stream water drainage. We conjecture that the present-day slow-down of WIS will evolve to shut-down in the next few decades, unless an addition of basal water prevents freeze-on-driven bed strengthening.

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Surface Features of Ice Stream B, Marie Byrd Land, West Antarctica

Annals of Glaciology ◽

10.3189/s0260305500001385 ◽

1986 ◽

Vol 8 ◽

pp. 168-170 ◽

Cited By ~ 14

Author(s):

P.L. Vornberger ◽

I.M. Whillans

Keyword(s):

Aerial Photographs ◽

Relative Importance ◽

West Antarctica ◽

Ice Streams ◽

Longitudinal Compression ◽

West Antarctic Ice Sheet ◽

Surface Features ◽

West Antarctic ◽

Ice Stream ◽

Ice Stream B

Aerial photographs have been obtained of Ice Stream B, one of the active ice streams draining the West Antarctic Ice Sheet. A sketch map made from these photographs shows two tributaries. The margin of the active ice is marked by curved crevasses and intense crevassing occurs just inward of them. Transverse crevasses dominate the center of the ice streams and diagonal types appear at the lower end. A “suture zone” originates at the tributary convergence and longitudinal surface ridges occur at the downglacier end. The causes of these surface features are discussed and the relative importance of four stresses in resisting the driving stress is assessed. We conclude that basal drag may be important, longitudinal compression is probably important at the lower end, and longitudinal tension is probably most important near the head of the ice stream. Side drag leads to shearing at the margins, but does not restrain much of the ice stream.

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Basal mechanics of ice streams: Insights from the stick-slip motion of Whillans Ice Stream, West Antarctica

Journal of Geophysical Research Atmospheres ◽

10.1029/2008jf001035 ◽

2009 ◽

Vol 114 (F1) ◽

Cited By ~ 63

Author(s):

J. Paul Winberry ◽

Sridhar Anandakrishnan ◽

Richard B. Alley ◽

Robert A. Bindschadler ◽

Matt A. King

Keyword(s):

West Antarctica ◽

Ice Streams ◽

Stick Slip ◽

Ice Stream ◽

Whillans Ice Stream ◽

Stick Slip Motion ◽

Slip Motion

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Ice stream or not? Radio-echo sounding of Carlson Inlet, West Antarctica

The Cryosphere ◽

10.5194/tc-5-907-2011 ◽

2011 ◽

Vol 5 (4) ◽

pp. 907-916 ◽

Cited By ~ 11

Author(s):

E. C. King

Keyword(s):

West Antarctica ◽

Ice Streams ◽

Basal Resistance ◽

Bed Topography ◽

Ice Stream ◽

Time Period ◽

Adjacent Part ◽

Radio Echo Sounding ◽

History Of ◽

Fast Flow

Abstract. The Antarctic Ice Sheet loses mass to the surrounding ocean mainly by drainage through a network of ice streams: fast-flowing glaciers bounded on either side by ice flowing one or two orders of magnitude more slowly. Ice streams flow despite low driving stress because of low basal resistance but are known to cease flowing if the basal conditions change, which can take place when subglacial sediment becomes dewatered by freezing or by a change in hydraulic pathways. Carlson Inlet, Antarctica has been interpreted as a stagnated ice stream, based on surface and basal morphology and shallow radar reflection profiling. To resolve the question of whether the flow history of Carlson Inlet has changed in the past, I conducted a ground-based radar survey of Carlson Inlet, the adjacent part of Rutford Ice Stream, and Talutis Inlet, West Antarctica. This survey provides details of the internal ice stratigraphy and allows the flow history to be interpreted. Tight folding of isochrones in Rutford Ice Stream and Talutis Inlet is interpreted to be the result of lateral compression during convergent flow from a wide catchment into a narrow, fast-flowing trunk. In contrast, the central part of Carlson Inlet has gently-folded isochrones that drape over the bed topography, suggestive of local accumulation and slow flow. A 1-D thermo-mechanical model was used to estimate the age of the ice. I conclude that the ice in the centre of Carlson Inlet has been near-stagnant for between 3500 and 6800 yr and that fast flow has not occurred there during that time period.

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Thickness changes on Whillans Ice Stream and Ice Stream C, West Antarctica, derived from laser altimeter measurements

Journal of Glaciology ◽

10.3189/172756503781830683 ◽

2003 ◽

Vol 49 (165) ◽

pp. 223-230 ◽

Cited By ~ 13

Author(s):

Vandy Blue Spikes ◽

Beáta M. Csatho ◽

Gordon S. Hamilton ◽

Ian M. Whillans

Keyword(s):

Average Rate ◽

West Antarctica ◽

Laser Altimeter ◽

Equivalent Thickness ◽

Thickness Change ◽

Airborne Laser ◽

Ice Stream ◽

Whillans Ice Stream ◽

Elevation Changes ◽

Global Sea Level

AbstractRepeat airborne laser altimeter measurements are used to derive surface elevation changes on parts of Whillans Ice Stream and Ice Stream C, West Antarctica. Elevation changes are converted to estimates of ice equivalent thickness change using local accumulation rates, surface snow densities and vertical bedrock motions. The surveyed portions of two major tributaries of Whillans Ice Stream are found to be thinning almost uniformly at an average rate of ∼1 m a−1. Ice Stream C has a complicated elevation-change pattern, but is generally thickening. These results are used to estimate the contribution of each surveyed region to the current rate of global sea-level rise.

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Melting and freezing beneath the Ross ice streams, Antarctica

Journal of Glaciology ◽

10.3189/172756504781830295 ◽

2004 ◽

Vol 50 (168) ◽

pp. 96-108 ◽

Cited By ~ 75

Author(s):

Ian Joughin ◽

Slawek Tulaczyk ◽

Douglas R. MacAyeal ◽

Hermann Engelhardt

Keyword(s):

Steady Flow ◽

Temperature Model ◽

West Antarctica ◽

Ice Streams ◽

Horizontal Advection ◽

Ice Stream ◽

Whillans Ice Stream ◽

Shear Heating ◽

Strain Heating ◽

Inland Ice

AbstractWe have estimated temperature gradients and melt rates at the bottom of the ice streams in West Antarctica. Measured velocities were used to include the effects of horizontal advection and strain heating in the temperature model and to determine shear heating at the bed. Our modeled temperatures agree well with measured temperatures from boreholes in regions of steady flow. We find that ice-stream tributaries and the inland ice account for about 87% of the total melt generated beneath the Ross ice streams and their catchments. Our estimates indicate that the ice plains of Whillans Ice Stream and Ice Stream C (even when active) have large areas subject to basal freezing, confirming earlier estimates that import of water from upstream is necessary to sustain motion. The relatively low melt rates on Whillans Ice Stream are consistent with observations of deceleration over the last few decades and suggest a shutdown may take place in the future, possibly within this century. While there are pockets of basal freezing beneath Ice Streams D and E, there are larger areas of basal melt that produce enough melt to more than offset the freezing, which is consistent with inferences of relatively steady flow for these ice streams over the last millennium.

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Continued deceleration of Whillans Ice Stream, West Antarctica

Geophysical Research Letters ◽

10.1029/2005gl024319 ◽

2005 ◽

Vol 32 (22) ◽

pp. n/a-n/a ◽

Cited By ~ 58

Author(s):

I. Joughin ◽

R. A. Bindschadler ◽

M. A. King ◽

D. Voigt ◽

R. B. Alley ◽

...

Keyword(s):

West Antarctica ◽

Ice Stream ◽

Whillans Ice Stream

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Scale independence of till rheology

Journal of Glaciology ◽

10.3189/172756506781828601 ◽

2006 ◽

Vol 52 (178) ◽

pp. 377-380 ◽

Cited By ~ 37

Author(s):

Slawek Tulaczyk

Keyword(s):

Characteristic Length ◽

West Antarctica ◽

Ice Flow ◽

Length Scales ◽

Ice Stream ◽

In Situ Experiments ◽

Whillans Ice Stream ◽

Speed Up

AbstractRepresentation of till rheology in glaciological models of ice motion over deformable sediments has, until now, focused largely on two end-member cases: (1) linear, or mildly non-linear, viscous rheology and (2) (nearly) plastic rheology. Most laboratory and in situ experiments support the latter model. Hindmarsh (1997) and Fowler (2002, 2003) proposed that experimental results represent the behavior of small till samples (characteristic length scales of ~0.1 to ~1 m) but that till behaves viscously over length scales that are relevant to determination of ice-flow rates in glaciers and ice sheets (~1 km or more). Observations of short speed-up events on the ice plain of Whillans Ice Stream, West Antarctica, provide an opportunity to compare the in situ rheology of this till, integrated over ~10–100 km, with the rheology of till from beneath the same ice stream determined on small laboratory samples and in local borehole experiments. This comparison indicates that the rheology of the subglacial till beneath Whillans Ice Stream is independent of scale.

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