Ice Stream-Ice Shelf Interaction in West Antarctica

AbstractWe use a finite-element model of coupled ice-stream/ice-shelf flow to study the sensitivity of Pine Island Glacier, West Antarctica, to changes in ice-shelf and basal conditions. By tuning a softening coefficient of the ice along the glacier margins, and a basal friction coefficient controlling the distribution of basal shear stress underneath the ice stream, we are able to match model velocity to that observed with interferometric synthetic aperture radar (InSAR). We use the model to investigate the effect of small perturbations on ice flow. We find that a 5.5–13% reduction in our initial ice-shelf area increases the glacier velocity by 3.5–10% at the grounding line. The removal of the entire ice shelf increases the grounding-line velocity by > 70%. The changes in velocity associated with ice-shelf reduction are felt several tens of km inland. Alternatively, a 5% reduction in basal shear stress increases the glacier velocity by 13% at the grounding line. By contrast, softening of the glacier side margins would have to be increased a lot more to produce a comparable change in ice velocity. Hence, both the ice-shelf buttressing and the basal shear stress contribute significant resistance to the flow of Pine Island Glacier.

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Flow dynamics of the Rutford Ice Stream ice-drainage basin, West Antarctica, from radar stratigraphy

Annals of Glaciology ◽

10.3189/172756409789097586 ◽

2009 ◽

Vol 50 (51) ◽

pp. 42-48 ◽

Cited By ~ 11

Author(s):

E.C. King

Keyword(s):

Drainage Basin ◽

Rapid Change ◽

Flow Dynamics ◽

Volume Flux ◽

West Antarctica ◽

Ice Shelf ◽

Main Trunk ◽

Ice Dynamics ◽

Ice Volume ◽

Ice Stream

AbstractRutford Ice Stream, West Antarctica, drains a catchment of >45 000 km2 into the Ronne Ice Shelf through a 26 km wide, 2.4 km deep subglacial trough adjacent to the Ellsworth Mountains. Forty-two per cent of its catchment boundary is common with Pine Island Glacier, where rapid change to ice dynamics is currently underway. These changes may eventually affect adjacent catchments such as Rutford. Radar sounding data were acquired over the Rutford ice-drainage basin that show the internal structure. In particular, distinctive reflector groups were identified that mark the boundaries between four different flow elements. The flow-margin reflector groups include curvilinear events that cross-cut isochrones and are therefore likely to be post-depositional. These reflections may arise from crystal orientation fabrics generated by localized strain in a flow margin. One of the sectors of the ice-drainage basin supplies the largest share (38%) of the ice volume flux through the main trunk of Rutford Ice Stream. This sector may be preferentially affected by continuing surface lowering in the Pine Island Glacier catchment.

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Ice-shelf flexure and tidal forcing of Bindschadler Ice Stream, West Antarctica

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2014.03.049 ◽

2014 ◽

Vol 395 ◽

pp. 184-193 ◽

Cited By ~ 6

Author(s):

Ryan T. Walker ◽

Byron R. Parizek ◽

Richard B. Alley ◽

Kelly M. Brunt ◽

Sridhar Anandakrishnan

Keyword(s):

West Antarctica ◽

Ice Shelf ◽

Tidal Forcing ◽

Ice Stream

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

Journal of Glaciology ◽

10.3189/s0022143000016440 ◽

1993 ◽

Vol 39 (133) ◽

pp. 553-561 ◽

Cited By ~ 23

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.

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Changes in the ice plain of Whillans Ice Stream, West Antarctica

Journal of Glaciology ◽

10.3189/172756505781829070 ◽

2005 ◽

Vol 51 (175) ◽

pp. 620-636 ◽

Cited By ~ 17

Author(s):

Robert Bindschadler ◽

Patricia Vornberger ◽

Laurence Gray

Keyword(s):

West Antarctica ◽

Ice Shelf ◽

Ross Ice Shelf ◽

Ice Stream ◽

Whillans Ice Stream ◽

Grounding Line ◽

Local Areas ◽

The Mean ◽

Geometric Changes ◽

Thinning Rate

AbstractData from the mouth of the decelerating Whillans Ice Stream (WIS), West Antarctica, spanning 42 years are reviewed. Deceleration has continued, with local areas of both thinning and thickening occurring. The mean thinning rate is 0.48 ± 0.77 ma–1. No consistent overall pattern is observed. Ice thickens immediately upstream of Crary Ice Rise where deceleration and divergence are strongest, suggesting expanded upstream influence of the ice rise. Thinning is prevalent on the Ross Ice Shelf. Grounding-line advance at a rate of 0.3 km a–1 is detected in a few locations. Basal stresses vary across an ice-stream transect with a zone of enhanced flow at the margin. Marginal shear is felt at the ice-stream center. Mass-balance values are less negative, but larger errors of earlier measurements mask any possible temporal pattern. Comparisons of the recent flow field with flow stripes suggest WIS contributes less ice to the deep subglacial channel carved by Mercer Ice Stream and now flows straighter. The general lack of geometric changes suggests that the regional velocity decrease is due to changing basal conditions.

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Grounding zone subglacial properties from calibrated active-source seismic methods

The Cryosphere ◽

10.5194/tc-15-1863-2021 ◽

2021 ◽

Vol 15 (4) ◽

pp. 1863-1880

Author(s):

Huw J. Horgan ◽

Laurine van Haastrecht ◽

Richard B. Alley ◽

Sridhar Anandakrishnan ◽

Lucas H. Beem ◽

...

Keyword(s):

Coefficient Of Determination ◽

Seismic Sources ◽

West Antarctica ◽

Ice Shelf ◽

Factors Affecting ◽

Shear Wave Velocities ◽

Active Source ◽

Seismic Methods ◽

Ice Stream ◽

Water Layers

Abstract. The grounding zone of Whillans Ice Stream, West Antarctica, exhibits an abrupt transition in basal properties from the grounded ice to the ocean cavity over distances of less than 0.5–1 km. Active-source seismic methods reveal the downglacier-most grounded portion of the ice stream is underlain by a relatively stiff substrate (relatively high shear wave velocities of 1100±430 m s−1) compared to the deformable till found elsewhere beneath the ice stream. Changes in basal reflectivity in our study area cannot be explained by the stage of the tide. Several kilometres upstream of the grounding zone, layers of subglacial water are detected, as are regions that appear to be water layers but are less than the thickness resolvable by our technique. The presence of stiff subglacial sediment and thin water layers upstream of the grounding zone supports previous studies that have proposed the dewatering of sediment within the grounding zone and the trapping of subglacial water upstream of the ocean cavity. The setting enables calibration of our methodology using returns from the floating ice shelf. This allows a comparison of different techniques used to estimate the sizes of the seismic sources, a constraint essential for the accurate recovery of subglacial properties. We find a strong correlation (coefficient of determination=0.46) between our calibrated method and a commonly used multiple-bounce method, but our results also highlight the incomplete knowledge of other factors affecting the amplitude of seismic sources and reflections in the cryosphere.

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New and improved determinations of velocity of Ice Streams B and C, West Antarctica

Journal of Glaciology ◽

10.3189/s0022143000016373 ◽

1993 ◽

Vol 39 (133) ◽

pp. 483-590 ◽

Cited By ~ 6

Author(s):

I. M. Whillans ◽

C.J. Van Der Veen

Keyword(s):

Stream Flow ◽

West Antarctica ◽

Ice Shelf ◽

Ice Streams ◽

Ice Flow ◽

Ice Stream ◽

Fast Ice ◽

Ice Stream B ◽

Shelf Flow ◽

Streaming Flow

AbstractMeasurements of velocity have been made on and next to Ice Streams Β and C, West Antarctica. The results are more precise than previous work and constitute a 93% increase in the number of values. These velocities are used to describe the confluence of flow into the ice streams and the development of fast ice-stream flow. The onset of fast-streaming flow occurs in many separate tributaries that coalesce down-glacier into the major ice streams. For those inter-stream ridges that have been studied, the flow is consistent with steady state. Along Ice Stream B, gradients in longitudinal stress offer little resistance to the ice flow. The transition from basal-drag control to ice-shelf flow is achieved through reduced drag at the glacier base and increased resistance associated with lateral drag. Velocities in the trunk of Ice Stream C are nearly zero but those at the up-glacial head are similar to those at the head of Ice Stream B.

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New and improved determinations of velocity of Ice Streams B and C, West Antarctica

Journal of Glaciology ◽

10.1017/s0022143000016373 ◽

1993 ◽

Vol 39 (133) ◽

pp. 483-590 ◽

Cited By ~ 87

Author(s):

I. M. Whillans ◽

C.J. Van Der Veen

Keyword(s):

Stream Flow ◽

West Antarctica ◽

Ice Shelf ◽

Ice Streams ◽

Ice Flow ◽

Ice Stream ◽

Fast Ice ◽

Ice Stream B ◽

Shelf Flow ◽

Streaming Flow

Abstract Measurements of velocity have been made on and next to Ice Streams Β and C, West Antarctica. The results are more precise than previous work and constitute a 93% increase in the number of values. These velocities are used to describe the confluence of flow into the ice streams and the development of fast ice-stream flow. The onset of fast-streaming flow occurs in many separate tributaries that coalesce down-glacier into the major ice streams. For those inter-stream ridges that have been studied, the flow is consistent with steady state. Along Ice Stream B, gradients in longitudinal stress offer little resistance to the ice flow. The transition from basal-drag control to ice-shelf flow is achieved through reduced drag at the glacier base and increased resistance associated with lateral drag. Velocities in the trunk of Ice Stream C are nearly zero but those at the up-glacial head are similar to those at the head of Ice Stream B.

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Basal sliding of Ice Stream B, West Antarctica

Journal of Glaciology ◽

10.3189/s0022143000002562 ◽

1998 ◽

Vol 44 (147) ◽

pp. 223-230 ◽

Cited By ~ 8

Author(s):

Engelhardt Hermann ◽

Kamb Barclay

Keyword(s):

West Antarctica ◽

Ice Shelf ◽

The West ◽

Ross Ice Shelf ◽

Sliding Motion ◽

Ice Stream ◽

Grounding Line ◽

Basal Sliding ◽

Ice Stream B ◽

Streaming Motion

AbstractA “tethered stake” apparatus is used to measure basal sliding in a borehole on Ice Stream B, West Antaretica, about 300 km upstream (east) from its grounding line near the head of the Ross Ice Shelf. A metal stake, emplaced at the top of a laver of unfrozen till underlying the ice, is connected by a tether line to a metering unit that measures the tether line as it is pulled out from the borehole by the stake as a result of basal sliding. The measured sliding motion includes any actual slip across the ice–till interface and may include in addition a possible contribution from shear deformation of till within about 3 cm of the interface. This 3 cm figure follows from a qualitative model of the movements of the stake in the course of the experiment, based on features of the record of apparent sliding. Alternative but less likely models would increase the figure from 3 cm to 10 cm or 25 cm. In any case it is small compared to the seismically inferred till thickness of 9 m. Measured apparent sliding averages 69% of the total motion of 1.2 m d−1over 26 days of observation if a 3.5 day period of slow apparent sliding (8% of the total motion) is included in the average. The occurrence of the slow period raises the possibility that the sliding motion switches back and forth between c.80% and c. 8% of the total motion, on a time-scale of a few days. However, it is likely that the period of slow apparent sliding represents instead a period when the stake got caught on the ice sole. If the slow period is therefore omitted, the indicated average basal sliding rate is 83% of the total motion. In either case, basal sliding predominates as the cause of the rapid ice-stream motion. In the last 2 days of observation the average apparent sliding rate reached 1.17 m d−1, essentially 100% of the motion of the ice stream. If till deformation contributes significantly to the ice-stream motion, the contribution is concentrated in a shear zone 3 cm to possibly 25 cm thick at the top of the 9 m thick till layer. These observations, if applicable to the West Antaretic ice sheet in general, pose complications in modeling the rapid ice-streaming motion.

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