scholarly journals Spatial stability of Ice Stream D and its tributaries, West Antarctica, revealed by radio-echo sounding and interferometry

2003 ◽  
Vol 37 ◽  
pp. 377-382 ◽  
Author(s):  
Martin J. Siegert ◽  
Antony J. Payne ◽  
Ian Joughin
Keyword(s):  
Interferometric Synthetic Aperture Radar ◽  
Internal Layers ◽  
Lateral Migration ◽  
West Antarctica ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Surface ◽  
Ice Stream ◽  
Radio Echo Sounding ◽  
Echo Sounding

AbstractIt has been shown recently that ice streams are fed by fast-flowing tributaries occupying well-defined subglacial troughs and with shared source areas. Here, ice-penetrating radio-echo sounding (RES) data are analyzed in conjunction with ice surface velocities derived from interferometric synthetic aperture radar (InSAR), to determine the englacial properties of tributaries feeding Ice Stream D, West Antarctica. All of Ice Stream D’s tributaries are coincident with “buckled” internal ice-sheet layers, most probably deformed by the processes responsible for enhanced ice flow. Between the tributaries well-preserved internal layers occur. The data reveal that no lateral migration of the ice-stream tributaries has occurred recently. This is consistent with thermomechanical ice-flow modelling, which indicates that the flow of Ice Stream D is controlled by a subglacial trough and is unaffected by changes to the flow of neighbouring Ice Stream C.

scholarly journals Elevation of ice-stream margin scars after stagnation

2000 ◽  
Vol 46 (152) ◽  
pp. 111-118 ◽  
Author(s):  
N. A. Nereson
Keyword(s):  
Finite Difference ◽  
Flow Model ◽  
Small Scale ◽  
West Antarctica ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Surface ◽  
Ice Stream ◽  
Adjustment Time ◽  
Siple Dome

AbstractThe evolution of an inter-ice-stream ridge flanked by stagnated ice streams is simulated using a finite-difference, continuity ice-flow model. The model tracks the elevation of small-scale topographic undulations on the ice surface (“scars”) which form at ice-stream margins, and shows that after ice-stream stagnation these surface features are lifted onto the flanks of the evolving ridge before they are carried downslope by ice flow. The model is applied to the stagnant ice streams bounding Siple Dome, West Antarctica: “Siple Ice Stream” (SIS) on the northeast flank near Ice Stream D, and the “Duckfoot” area (DF) on the south flank near Ice Stream C. The volume-adjustment time-scale corresponding to the evolution of Siple Dome and these stagnant ice-stream areas is 1500–2000 years. The present geometry and elevation of the scar features, in addition to measurements of the present mass flux across the ridge, are used to estimate stagnation ages for SIS and DF. These measurements suggest that both SIS and DF stagnated 200–500 years ago.

scholarly journals Anisotropic ice flow leading to the onset of Ice Stream D, West Antarctica: numerical modelling based on the observations from Byrd Station borehole

2003 ◽  
Vol 37 ◽  
pp. 397-403 ◽  
Author(s):  
Weili Wang ◽  
H. Jay Zwally ◽  
Christina L. Hulbe ◽  
Martin J. Siegert ◽  
Ias Joughin
Keyword(s):  
Crystal Orientation ◽  
Internal Layers ◽  
Fabric Anisotropy ◽  
West Antarctica ◽  
Ice Flow ◽  
Ice Stream ◽  
Radio Echo Sounding ◽  
The Last Glacial Maximum ◽  
Particle Paths ◽  
The Last Glacial

AbstractAn ice-sheet flowline model is used to simulate the flow of ice along two particle paths toward the onset to Ice Stream D, West Antarctica. One path is near the centre line of the main tributary to the ice stream, while the second passes by the Byrd Station borehole site. In this paper, we analyze the flow of the moderately fast-flowing tributaries in terms of ice-fabric anisotropy and estimate the steady-state ice-flow regions with the compatible developed crystal orientation fabrics along two particle paths. Comparison between modelled isochrones and internal layers detected from radio-echo sounding surveys in the area is used to suggest that flow upstream of the onset to Ice Stream D appears to have been stable since at least the Last Glacial Maximum.

scholarly journals Characteristics of Ice Flow in Marie Byrd Land, Antarctica

1979 ◽  
Vol 24 (90) ◽  
pp. 63-75 ◽  
Author(s):  
K. E. Rose
Keyword(s):  
Flow Line ◽  
Landsat Imagery ◽  
Ice Sheet ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Flow ◽  
Ross Ice Shelf ◽  
Radio Echo Sounding ◽  
Echo Sounding

AbstractExtensive radio echo-sounding has mapped the part of West Antarctica between Byrd Station, the Whitmore Mountains, the Transantarctic Mountains, and the Ross Ice Shelf. The ice sheet in this area is dominated by five major sub-parallel ice streams (A–E), which are up to 100 km wide and extend inland from the grounding line of the Ross Ice Shelf for about 400 km. Their positions have been determined by crevassing seen on radio echo-sounding records, trimetrogon photographs, and Landsat imagery. The ice streams are characterized by their flat transverse cross-sections, while the intervening ice sheet exhibits domes and ridges. Ice flow lines are defined from the ice-surface contour pattern and the trend of the ice streams. It is apparent from this work that the flow line passing through Byrd Station joins ice stream D.The bedrock of the area is relatively smooth near the Ross Ice Shelf, becoming rougher near Byrd Station and especially so near the Whitmore Mountains. Bedrock troughs, which control the positions of the ice streams, are believed to have a tectonic origin.In this paper the role of the ice streams in the glaciological regime of West Antarctica is investigated from radio-echo data and estimates of balance velocity, basal shear stress, and basal temperatures.

scholarly journals Characteristics of Ice Flow in Marie Byrd Land, Antarctica

1979 ◽  
Vol 24 (90) ◽  
pp. 63-75 ◽  
Author(s):  
K. E. Rose
Keyword(s):  
Flow Line ◽  
Landsat Imagery ◽  
Ice Sheet ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Flow ◽  
Ross Ice Shelf ◽  
Radio Echo Sounding ◽  
Echo Sounding

AbstractExtensive radio echo-sounding has mapped the part of West Antarctica between Byrd Station, the Whitmore Mountains, the Transantarctic Mountains, and the Ross Ice Shelf. The ice sheet in this area is dominated by five major sub-parallel ice streams (A–E), which are up to 100 km wide and extend inland from the grounding line of the Ross Ice Shelf for about 400 km. Their positions have been determined by crevassing seen on radio echo-sounding records, trimetrogon photographs, and Landsat imagery. The ice streams are characterized by their flat transverse cross-sections, while the intervening ice sheet exhibits domes and ridges. Ice flow lines are defined from the ice-surface contour pattern and the trend of the ice streams. It is apparent from this work that the flow line passing through Byrd Station joins ice stream D.The bedrock of the area is relatively smooth near the Ross Ice Shelf, becoming rougher near Byrd Station and especially so near the Whitmore Mountains. Bedrock troughs, which control the positions of the ice streams, are believed to have a tectonic origin.In this paper the role of the ice streams in the glaciological regime of West Antarctica is investigated from radio-echo data and estimates of balance velocity, basal shear stress, and basal temperatures.

scholarly journals Bed reflectivity beneath inactive ice streams in West Antarctica

2003 ◽  
Vol 36 ◽  
pp. 287-291 ◽  
Author(s):  
Ginny A. Catania ◽  
Howard B. Conway ◽  
Anthony M. Gades ◽  
Charles F. Raymond ◽  
Hermann Engelhardt
Keyword(s):  
Water System ◽  
West Antarctica ◽  
Ice Streams ◽  
Weak Measurements ◽  
Ice Stream ◽  
Spatial Changes ◽  
Geometric Spreading ◽  
Radio Echo Sounding ◽  
Measured Power ◽  
Echo Sounding

AbstractRadio-echo sounding (RES) techniques are used to examine spatial changes in bed reflectivity across relict ice streams inWest Antarctica. Measurements from adjacent interstream ridges are used to correct the measured power returned from the bed for attenuation and losses due to geometric spreading, scattering and absorption. RES measurements near boreholes drilled on Ice Stream C (ISC) indicate high coefficients of bed reflectivity (R > 0.1) in locations where the bed was thawed and boreholes connected to the basal water system, and low reflectivity coefficients (R < 0.02) at locations that were frozen and not connected. Intermediate values of bed reflectivity were measured at locations where the connection to the basal water system was weak. Measurements across four relict margins show that bed reflectivity usually jumps from low to high values several kilometers inside the outermost buried crevasses. We interpret this to be a transition from frozen to thawed basal conditions and discuss implications of these observations.

scholarly journals The englacial stratigraphy of Wilkes Land, East Antarctica, as revealed by internal radio-echo sounding layering, and its relationship with balance velocities

2003 ◽  
Vol 36 ◽  
pp. 189-196 ◽  
Author(s):  
David M. Rippin ◽  
Martin J. Siegert ◽  
Jonathan L. Bamber
Keyword(s):  
East Antarctica ◽  
Internal Layers ◽  
Ice Streams ◽  
Ice Flow ◽  
Wilkes Land ◽  
Radio Echo Sounding ◽  
Flow Features ◽  
Depth Dependency ◽  
Fast Flow ◽  
Echo Sounding

AbstractThe disruption of internal layering visible in radio-echo sounding (RES) data from East Antarctica has, to date, been attributed to ice flow around bedrock topography. However, observations of internal layer disruption in the Siple Coast ice streams of West Antarctica have led to the suggestion that increased strain at the margins of ice streams may also be responsible for the disruption of internal layers. Here we present a re-analysis of the extensive RES dataset collected between 1967 and 1979 over a large part of Wilkes Land, East Antarctica, and relate the location of continuous and disrupted internal layers to modelled balance velocities. We show that the mean balance velocity associated with all areas of disrupted layers is 2.5 times higher than that associated with areas of continuous layers. We also demonstrate that disrupted layers are associated not only with ice streams, but also with areas of enhanced ice flow, which penetrate inland from the grounding line up to several hundred kilometres into the interior of East Antarctica. Continuous layers always overlie disrupted layers, suggesting either a depth dependency in the process responsible for layer disruption, or subsequent deposition of continuous layers. In some cases, disrupted layers occur outside fast-flow features, and continuous layers occur within fast-flow features. Such regions are explained by short-term flow patterns, but might also be attributed to inaccuracies in the balance-velocity calculations.

scholarly journals Bed properties of Siple Dome and adjacent ice streams, West Antarctica, inferred from radio-echo sounding measurements

2000 ◽  
Vol 46 (152) ◽  
pp. 88-94 ◽  
Author(s):  
A. M. Gades ◽  
C. F. Raymond ◽  
H. Conway ◽  
R. W. Jagobel
Keyword(s):  
Basal Layer ◽  
Water Layer ◽  
Thickness Variation ◽  
West Antarctica ◽  
Ice Streams ◽  
A Value ◽  
Ice Stream ◽  
Siple Dome ◽  
Radio Echo Sounding ◽  
Echo Sounding

AbstractWe have used ground-based radio-echo sounding (RES) profiles to reveal the spatial distribution of basal and internal ice properties across Siple Dome, West Antarctica, and under the dormant ice streams on its flanks. The RES-detected bed-reflection power, corrected for the effects of instrumentation and ice-thickness variation, is nearly constant across Siple Dome at a value suggesting spatially homogeneous basal properties of ice frozen to bedrock. Till, if present under the dome, must be thin (<0.1 m). The high basal reflectivity measured under now dormant “Siple Ice Stream” (SIS) and Ice Stream C suggests that they are underlain by either a thin (<0.05 m) water layer or a thick (>1 m) thawed or frozen till layer. The evidence that the dormant SIS is not frozen directly to underlying bedrock (but is separated by a water or till layer) is a further indication that it was once an active ice stream, and suggests that streaming motion may have ceased before the basal layer was frozen. The absence of a thick till layer beneath Siple Dome is consistent with its apparent stability as an inter-ice-stream ridge in the past and may suggest that it will remain as a stable limitation of ice-stream width in the future.

scholarly journals Of isbræ and ice streams

2003 ◽  
Vol 36 ◽  
pp. 66-72 ◽  
Author(s):  
Martin Truffer ◽  
Keith A. Echelmeyer
Keyword(s):  
Ice Sheet ◽  
Shear Zones ◽  
West Antarctica ◽  
Ice Streams ◽  
Ice Flow ◽  
Bed Topography ◽  
Ice Stream ◽  
Fast Ice ◽  
Fast Flow ◽  
End Members

AbstractFast-flowing ice streams and outlet glaciers provide the major avenues for ice flow from past and present ice sheets. These ice streams move faster than the surrounding ice sheet by a factor of 100 or more. Several mechanisms for fast ice-stream flow have been identified, leading to a spectrum of different ice-stream types. In this paper we discuss the two end members of this spectrum, which we term the “ice-stream” type (represented by the Siple Coast ice streams in West Antarctica) and the “isbræ” type (represented by Jakobshavn Isbræ in Greenland). The typical ice stream is wide, relatively shallow (∼1000 m), has a low surface slope and driving stress (∼10 kPa), and ice-stream location is not strongly controlled by bed topography. Fast flow is possible because the ice stream has a slippery bed, possibly underlain by weak, actively deforming sediments. The marginal shear zones are narrow and support most of the driving stress, and the ice deforms almost exclusively by transverse shear. The margins seem to be inherently unstable; they migrate, and there are plausible mechanisms for such ice streams to shut down. The isbræ type of ice stream is characterized by very high driving stresses, often exceeding 200 kPa. They flow through deep bedrock channels that are significantly deeper than the surrounding ice, and have steep surface slopes. Ice deformation includes vertical as well as lateral shear, and basal motion need not contribute significantly to the overall motion. The marginal shear zone stend to be wide relative to the isbræ width, and the location of isbræ and its margins is strongly controlled by bedrock topography. They are stable features, and can only shut down if the high ice flux cannot be supplied from the adjacent ice sheet. Isbræs occur in Greenland and East Antarctica, and possibly parts of Pine Island and Thwaites Glaciers, West Antarctica. In this paper, we compare and contrast the two types of ice streams, addressing questions such as ice deformation, basal motion, subglacial hydrology, seasonality of ice flow, and stability of the ice streams.

scholarly journals Deformation in Rutford Ice Stream, West Antarctica: measuring shear-wave anisotropy from icequakes

2013 ◽  
Vol 54 (64) ◽  
pp. 105-114 ◽  
Author(s):  
S.R. Harland ◽  
J.-M. Kendall ◽  
G.W. Stuart ◽  
G.E. Lloyd ◽  
A.F. Baird ◽  
...  
Keyword(s):  
Shear Wave ◽  
Flow Direction ◽  
Transversely Isotropic ◽  
Shear Wave Splitting ◽  
Ice Crystal ◽  
West Antarctica ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Stream ◽  
Wave Splitting

Abstract Ice streams provide major drainage pathways for the Antarctic ice sheet. The stress distribution and style of flow in such ice streams produce elastic and rheological anisotropy, which informs ice-flow modelling as to how ice masses respond to external changes such as global warming. Here we analyse elastic anisotropy in Rutford Ice Stream, West Antarctica, using observations of shear-wave splitting from three-component icequake seismograms to characterize ice deformation via crystal-preferred orientation. Over 110 high-quality measurements are made on 41 events recorded at five stations deployed temporarily near the ice-stream grounding line. To the best of our knowledge, this is the first well-documented observation of shear-wave splitting from Antarctic icequakes. The magnitude of the splitting ranges from 2 to 80 ms and suggests a maximum of 6% shear-wave splitting. The fast shear-wave polarization direction is roughly perpendicular to ice-flow direction. We consider three mechanisms for ice anisotropy: a cluster model (vertical transversely isotropic (VTI) model); a girdle model (horizontal transversely isotropic (HTI) model); and crack-induced anisotropy (HTI model). Based on the data, we can rule out a VTI mechanism as the sole cause of anisotropy – an HTI component is needed, which may be due to ice crystal a-axis alignment in the direction of flow or the alignment of cracks or ice films in the plane perpendicular to the flow direction. The results suggest a combination of mechanisms may be at play, which represent vertical variations in the symmetry of ice crystal anisotropy in an ice stream, as predicted by ice fabric models.

scholarly journals Migration of the Siple Dome ice divide, West Antarctica

1998 ◽  
Vol 44 (148) ◽  
pp. 643-652 ◽  
Author(s):  
N. A. Nereson ◽  
C. F. Raymond ◽  
E. D. Waddington ◽  
R. W. Jacobel
Keyword(s):  
Migration Rate ◽  
Internal Layer ◽  
Internal Layers ◽  
West Antarctica ◽  
Ice Streams ◽  
Ice Flow ◽  
Flow Models ◽  
The Past ◽  
Siple Dome ◽  
Local Accumulation

AbstractThe non-linearity of the ice-flow law or a local accumulation low over an ice divide can cause isochrones (internal layers) to be shallower under the divide relative to the flanks, forming a “divide bump” in the internal layer pattern. This divide signature is analyzed using ice-flow models and inverse techniques to detect and quantify motion of the Siple Dome ice divide, West Antarctica. The principal feature indicating that migration has occurred is a distinct tilt of the axis of the peaks of the warped internal layers beneath the divide. The calculated migration rate is 0.05-0.50 m a−1 toward Ice Stream D and depends slightly on whether the divide bump is caused by the non-linearity of ice flow or by a local accumulation low. Our calculations also suggest a strong south-north accumulation gradient of 5-10 x 10−6 a−1 in a narrow zone north of the divide. A consequence of divide migration is that pre-Holocene ice is thickest about 0.5 km south of the present divide position. Divide motion indicates that non-steady processes, possibly associated with activity of the bounding ice streams, are affecting the geometry of Siple Dome. The migration rate is sufficiently slow that the divide bump is maintained in the internal layer pattern at all observable depths. This suggests that major asynchronous changes in the elevation or position of the bounding ice streams are unlikely over at least the past 103-104 years.

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