scholarly journals Evidence of rapid subglacial water piracy under Whillans Ice Stream, West Antarctica

2013 ◽  
Vol 59 (218) ◽  
pp. 1147-1162 ◽  
Author(s):  
S.P. Carter ◽  
H.A. Fricker ◽  
M.R. Siegfried
Keyword(s):  
Numerical Models ◽  
Water System ◽  
Complex Nature ◽  
West Antarctica ◽  
Ice Streams ◽  
Ice Cloud ◽  
Lake Volume ◽  
Ice Stream ◽  
Whillans Ice Stream ◽  
Subglacial Lakes

AbstractThe subglacial water system of lower Whillans Ice Stream on the Siple Coast, West Antarctica, contains numerous connected subglacial lakes in three hydrological basins (northern, central and southern). We use Ice, Cloud and land Elevation Satellite (ICESat) data to derive estimates of lake volume change and regional thickness changes. By combining these results with a water budget model, we show that a uniform, localized thickness increase perturbed the hydropotential, resulting in a change in course of a major flow path within the system in 2005. Water originating from upper Whillans and Kamb Ice Streams that previously supplied the southern basin became diverted toward Subglacial Lake Whillans (SLW). This diversion led to a tenfold filling rate increase of SLW. Our observation suggests that water piracy may be common in the Siple Coast region, where the gentle basal relief makes the basal hydropotential particularly sensitive to small changes in ice thickness. Given the previously inferred connections between water piracy and ice-stream slowdown elsewhere in the region, the subtle and complex nature of this system presents new challenges for numerical models.

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

2009 ◽  
Vol 114 (F1) ◽  
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

scholarly journals Melting and freezing beneath the Ross ice streams, Antarctica

2004 ◽  
Vol 50 (168) ◽  
pp. 96-108 ◽  
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.

scholarly journals ‘Sticky spots’ and subglacial lakes under ice streams of the Siple Coast, Antarctica

2011 ◽  
Vol 52 (58) ◽  
pp. 18-22 ◽  
Author(s):  
Olga V. Sergienko ◽  
Christina L. Hulbe
Keyword(s):  
Numerical Models ◽  
Water Source ◽  
Surface Velocity ◽  
Ice Streams ◽  
Ice Flow ◽  
Stream Surface ◽  
Topographic Features ◽  
West Antarctic ◽  
Ice Stream ◽  
Subglacial Lakes

AbstarctLocations of subglacial lakes discovered under fast-moving West Antarctic ice streams tend to be associated with topographic features of the subglacial bed or with areas that have strong variations in basal conditions. Inversion of ice-stream surface velocity indicates that basal conditions under ice streams can be highly variable and that there can be widespread regions where basal traction is high. To seek an explanation for why lakes appear to be sited near areas with high basal traction, we use numerical models to simulate ice-stream dynamics, thermodynamics and subglacial water flow. We demonstrate that the ice flow over high basal traction areas produces favourable conditions for the ponding of meltwater. Energy dissipation associated with ice sliding over a region with high basal traction constitutes a water source supplying a lake, and ice-thickness perturbations induced by ice flow over variable traction create local minima in hydraulic potential. Variations in thermodynamic processes caused by such ice flow could be responsible for limiting the horizontal extent of the subglacial lakes.

scholarly journals Basal melt rates beneath Whillans Ice Stream, West Antarctica

2010 ◽  
Vol 56 (198) ◽  
pp. 647-654 ◽  
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.

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 Stick–slip behavior of ice streams: modeling investigations

2009 ◽  
Vol 50 (52) ◽  
pp. 87-94 ◽  
Author(s):  
Olga V. Sergienko ◽  
Douglas R. MacAyeal ◽  
Robert A. Bindschadler
Keyword(s):  
West Antarctica ◽  
Ice Streams ◽  
Stick Slip ◽  
Ice Stream ◽  
Whillans Ice Stream ◽  
Spatial Propagation ◽  
The Difference ◽  
Stick Slip Motion ◽  
Transitional Phase ◽  
Slip Motion

AbstractA puzzling phenomenon of ice-stream flow is the stick–slip motion displayed by Whillans Ice Stream (WIS), West Antarctica. In this study we test the hypothesis that the WIS stick–slip motion has features similar to those of other known stick–slip systems, and thus might be of the same origin. To do so, we adapt a simple mechanical model widely used in seismology to study classic stick–slip behavior observed in tectonic faults, in which the difference between static and dynamic friction allows for the generation and spatial propagation of abrupt slip events. We show how spatial variability in friction properties, as well as a periodic forcing intended to mimic the effect of tides, can reproduce the observed duration and periodicity of stick–slip motion in an ice stream. An intriguing aspect of the association of WIS with mechanical stick–slip oscillators is that the onset of stick–slip cycling from a condition of permanent slip appears to be associated with the reduction in overall speed of WIS. If this association is true, then stick–slip behavior of WIS is a transitional phase of behavior associated with the ice stream's recent deceleration.

scholarly journals Technologies for retrieving sediment cores in Antarctic subglacial settings

2016 ◽  
Vol 374 (2059) ◽  
pp. 20150056 ◽  
Author(s):  
Dominic A. Hodgson ◽  
Michael J. Bentley ◽  
James A. Smith ◽  
Julian Klepacki ◽  
Keith Makinson ◽  
...  
Keyword(s):  
Sediment Cores ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Stream ◽  
Whillans Ice Stream ◽  
History Of ◽  
Subglacial Lakes ◽  
Physical And Chemical ◽  
The Antarctic

Accumulations of sediment beneath the Antarctic Ice Sheet contain a range of physical and chemical proxies with the potential to document changes in ice sheet history and to identify and characterize life in subglacial settings. Retrieving subglacial sediments and sediment cores presents several unique challenges to existing technologies. This paper briefly reviews the history of sediment sampling in subglacial environments. It then outlines some of the technological challenges and constraints in developing the corers being used in sub-ice shelf settings (e.g. George VI Ice Shelf and Larsen Ice Shelf), under ice streams (e.g. Rutford Ice Stream), at or close to the grounding line (e.g. Whillans Ice Stream) and in subglacial lakes deep under the ice sheet (e.g. Lake Ellsworth). The key features of the corers designed to operate in each of these subglacial settings are described and illustrated together with comments on their deployment procedures.

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 Modeling 5 years of subglacial lake activity in the MacAyeal Ice Stream (Antarctica) catchment through assimilation of ICESat laser altimetry

2011 ◽  
Vol 57 (206) ◽  
pp. 1098-1112 ◽  
Author(s):  
Sasha P. Carter ◽  
Helen A. Fricker ◽  
Donald D. Blankenship ◽  
Jesse V. Johnson ◽  
William H. Lipscomb ◽  
...  
Keyword(s):  
Water Distribution ◽  
Large Scale ◽  
Transport Model ◽  
Laser Altimetry ◽  
Volume Changes ◽  
Ice Streams ◽  
Subglacial Lake ◽  
Lake Volume ◽  
Ice Stream ◽  
Subglacial Lakes

AbstractSubglacial lakes beneath Antarctica’s fast-moving ice streams are known to undergo ∼1 km3 volume changes on annual timescales. Focusing on the MacAyeal Ice Stream (MacIS) lake system, we create a simple model for the response of subglacial water distribution to lake discharge events through assimilation of lake volume changes estimated from Ice, Cloud and land Elevation Satellite (ICESat) laser altimetry. We construct a steady-state water transport model in which known subglacial lakes are treated as either sinks or sources depending on the ICESat-derived filling or draining rates. The modeled volume change rates of five large subglacial lakes in the downstream portion of MacIS are shown to be consistent with observed filling rates if the dynamics of all upstream lakes are considered. However, the variable filling rate of the northernmost lake suggests the presence of an undetected lake of similar size upstream. Overall, we show that, for this fast-flowing ice stream, most subglacial lakes receive >90% of their water from distant distributed sources throughout the catchment, and we confirm that water is transported from regions of net basal melt to regions of net basal freezing. Our study provides a geophysically based means of validating subglacial water models in Antarctica and is a potential way to parameterize subglacial lake discharge events in large-scale ice-sheet models where adequate data are available.

scholarly journals Basal melt beneath Whillans Ice Stream and Ice Streams A and C, West Antarctica

2003 ◽  
Vol 36 ◽  
pp. 257-262 ◽  
Author(s):  
Ian R. Joughin ◽  
Slawek Tulaczyk ◽  
Hermann F. Engelhardt
Keyword(s):  
Temperature Gradients ◽  
Shear Stresses ◽  
Temperature Profiles ◽  
West Antarctica ◽  
Ice Streams ◽  
Advection Diffusion Equation ◽  
Ice Stream ◽  
Single Temperature ◽  
Whillans Ice Stream ◽  
Basal Shear

AbstractWe have used a recently derived map of the velocity of Whillans Ice Stream and Ice Streams A and C, West Antarctica, to help estimate basal melt. Ice temperature was modeled with a simple vertical advection–diffusion equation,“tuned” to match temperature profiles. We find that most of the melt occurs beneath the tributaries, where larger basal shear stresses and thicker ice favor greater melt (e.g. 10–20mm a−1). The occurrence of basal freezing is predicted beneath much of the ice plains of Ice Stream C andWhillans Ice Stream. Modeled melt rates for when Ice Stream C was active suggest there was enough meltwater generated in its tributaries to balance basal freezing on its ice plain. Net basal melt for Whillans Ice Stream is greater due to less steep basal temperature gradients. Modeled temperatures on Whillans Ice Stream, however, were constrained by a single temperature profile at UpB. Basal temperature gradients for Whillans branch 1 and Ice Stream A may have conditions more similar to those beneath Ice Streams C and D, in which case, there may not be sufficient melt to sustain motion. This would be consistent with the steady deceleration of Whillans Ice Stream over the last few decades.

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