scholarly journals Mass Balance of Ice Stream B, West Antarctica

1988 ◽  
Vol 11 ◽  
pp. 187-193 ◽  
Author(s):  
I. M. Whillans ◽  
R. A. Bindschadler
Keyword(s):  
Mass Balance ◽  
Catchment Area ◽  
Accumulation Rate ◽  
Katabatic Wind ◽  
Stream Velocity ◽  
Beta Activity ◽  
West Antarctica ◽  
Gross Beta ◽  
Ice Stream ◽  
Ice Stream B

The mass balance of the drainage area of Ice Stream B, West Antarctica, is calculated from new measurements of both discharge and accumulation rate. The discharge is computed for a transverse section near the lower end of the ice stream. Velocities have been obtained for 787 sites, using repeated photogrammetry, with ground control by Transit (doppler) satellite tracking. Thicknesses have been obtained by radio echo-sounding. The uncertainties in the discharge calculations are only about 3%. Net accumulation is derived from profiles of gross beta activity and from identification of the 1954–55 and 1964–65 nuclear-bomb strata. The major uncertainties are associated with the identification of the catchment area and with the accumulation rate. Accumulation rate varies locally, probably due to the interaction of katabatic wind with local slope, and many spot measurements are needed to obtain a good regional mean. The integrated input is 21.4 ± 5.2 km3 a−1, and the output is 30.0 ± 1.0 km3 a−1. The deficit is thus 8.6 ± 6.2 km3 a−1, which corresponds to a mean thinning rate of 0.06 m a−1 ± 0.04 m a−1. The difference from earlier estimates is mainly due to the refined catchment area and accumulation. The imbalance is significant but smaller than previously calculated: for balance the accumulation rate or catchment area would need to be about 39% larger or the ice stream velocity would need to be 28% slower.

scholarly journals Mass Balance of Ice Stream B, West Antarctica

1988 ◽  
Vol 11 ◽  
pp. 187-193 ◽  
Author(s):  
I. M. Whillans ◽  
R. A. Bindschadler
Keyword(s):  
Mass Balance ◽  
Catchment Area ◽  
Accumulation Rate ◽  
Katabatic Wind ◽  
Stream Velocity ◽  
Beta Activity ◽  
West Antarctica ◽  
Gross Beta ◽  
Ice Stream ◽  
Ice Stream B

The mass balance of the drainage area of Ice Stream B, West Antarctica, is calculated from new measurements of both discharge and accumulation rate. The discharge is computed for a transverse section near the lower end of the ice stream. Velocities have been obtained for 787 sites, using repeated photogrammetry, with ground control by Transit (doppler) satellite tracking. Thicknesses have been obtained by radio echo-sounding. The uncertainties in the discharge calculations are only about 3%. Net accumulation is derived from profiles of gross beta activity and from identification of the 1954–55 and 1964–65 nuclear-bomb strata. The major uncertainties are associated with the identification of the catchment area and with the accumulation rate. Accumulation rate varies locally, probably due to the interaction of katabatic wind with local slope, and many spot measurements are needed to obtain a good regional mean. The integrated input is 21.4 ± 5.2 km3a−1, and the output is 30.0 ± 1.0 km3a−1. The deficit is thus 8.6 ± 6.2 km3a−1, which corresponds to a mean thinning rate of 0.06 m a−1± 0.04 m a−1. The difference from earlier estimates is mainly due to the refined catchment area and accumulation. The imbalance is significant but smaller than previously calculated: for balance the accumulation rate or catchment area would need to be about 39% larger or the ice stream velocity would need to be 28% slower.

scholarly journals Mass balance and accumulation rate across Siple Dome, West Antarctica

2002 ◽  
Vol 35 ◽  
pp. 102-106 ◽  
Author(s):  
Gordon S. Hamilton
Keyword(s):  
Mass Balance ◽  
Accumulation Rate ◽  
Snow Accumulation ◽  
Accumulation Rates ◽  
West Antarctica ◽  
Gross Beta ◽  
Thickness Change ◽  
Siple Dome ◽  
The Difference ◽  
Possible Cause

AbstractSnow-accumulation rates and rates of ice-thickness change (mass balance) are studied at several sites on Siple Dome,West Antarctica. Accumulation rates are derived from analyses of gross beta radioactivity in shallow firn cores located along a 60 km transect spanning both flanks and the crest of the dome. There is a north–south gradient in snow-accumulation rate across the dome that is consistent with earlier radar mapping of internal stratigraphy. Orographic processes probably control this distribution. Mass balance is inferred from the difference between global positioning system (GPS)-derived vertical velocities and snow-accumulation rates for sites close to the firn-core locations. Results indicate that there is virtually no net thickness change at four of the five sites. the exception is at the northernmost site where a small amount of thinning is detected, that appears to be inconsistent with other studies. A possible cause of this anomalous thinning is recent retreat of the grounding line of Ice Stream D.

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

1986 ◽  
Vol 8 ◽  
pp. 168-170 ◽  
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.

scholarly journals Radar reflections reveal a wet bed beneath stagnant Ice Stream C and a frozen bed beneath ridge BC, West Antarctica

1998 ◽  
Vol 44 (146) ◽  
pp. 149-156 ◽  
Author(s):  
C. R. Bentley ◽  
N. Lord ◽  
C. Liu
Keyword(s):  
Radar Data ◽  
Ice Thickness ◽  
West Antarctica ◽  
Ice Streams ◽  
Ice Stream ◽  
Crossover Analysis ◽  
Automated Processing ◽  
Basal Reflection ◽  
Field Season ◽  
Ice Stream B

AbstractDigital airborne radar data were collected during the 1987-88 Antarctic field season in nine gridded blocks covering the downstream portions of Ice Stream B (6km spacing) and Ice Stream C (11 km spacing), together with a portion of ridge BC between them. An automated processing procedure was used for picking onset times of the reflected radar pulses, converting travel times to distances, interpolating missing data, converting pressure transducer readings, correcting navigational drift, performing crossover analysis, and zeroing rémanent crossover errors. Interpolation between flight-lines was carried out using the minimum curvature method.Maps of ice thickness (estimated accuracy 20 m) and basal-reflection strength (estimated accuracy 1 dB) were produced. The ice-thickness map confirms the characteristics of previous reconnaissance maps and reveals no new features. The reflection-strength map shows pronounced contrasts between the ice streams and ridge BC and between the two ice streams themselves. We interpret the reflection strengths to mean that the bed of Ice Stream C, as well as that of Ice Stream B, is unfrozen, that the bed of ridge BC is frozen and that the boundary between the frozen bed of ridge BC and the unfrozen bed of Ice Stream C lies precisely below the former shear margin of the ice stream.

scholarly journals Seismic-Reflection Profiling of a Widespread Till Beneath Ice Stream B, West Antarctica (Abstract)

1988 ◽  
Vol 11 ◽  
pp. 210 ◽  
Author(s):  
Sean T. Rooney ◽  
D. D. Blankenship ◽  
R. B. Alley ◽  
C. R. Bentley
Keyword(s):  
Seismic Reflection ◽  
Ross Sea ◽  
High Porosity ◽  
West Antarctica ◽  
Ice Streams ◽  
Ice Flow ◽  
West Antarctic ◽  
Ice Stream ◽  
Seismic Reflection Profiling ◽  
Ice Stream B

Seismic-reflection profiling has previously shown that, at least at one location. Ice Stream Β in West Antarctica rests on a layer of till a few meters thick (Blankenship and others 1986). Analyses of both compressional- and shear-wave seismic reflections from the ice–till boundary confirm the results of those earlier studies, which showed that the till is water-saturated and has a high porosity and low differential pressure. We conclude that this till is basically homogeneous, at least on a scale of tens of kilometers, though some evidence that its properties vary laterally can be discerned in these data. We propose that the till is widespread beneath Ice Stream Β and probably also beneath the other West Antarctic ice streams. Our seismic profiling shows that the till is essentially continuous beneath Ice Stream Β over at least 12 km parallel to ice flow and 8 km transverse to flow. Beneath these profiles the till averages about 6.5 m thick and is present everywhere except possibly on isolated bedrock ridges parallel to ice flow. The till thickness on these bedrock ridges falls to less than 2 m, the limit of our seismic resolution, but there is evidence that the ridges do not impede ice flow substantially. The bedrock beneath the till is fluted parallel to flow, with flutes that are 10–13 m deep by 200–1000 m wide; we believe these flutes are formed by erosion beneath a deforming till. We also observe an angular unconformity at the base of the till, which is consistent with the idea that erosion is occurring there. The sedimentary record in the Ross Embayment looks very similar to that beneath Ice Stream B, i.e. a few meters of till resting unconformably (the Ross Sea unconformity) on lithified sedimentary rock, and we postulate that the Ross Sea unconformity was generated by erosion beneath a grounded ice sheet by a deforming till.

scholarly journals Large spatial variation in accumulation rate in Jutulstraumen ice stream, Dronning Maud Land, Antarctica

1998 ◽  
Vol 27 ◽  
pp. 231-238 ◽  
Author(s):  
Kjetil Melvold ◽  
Jon Ove Hagen ◽  
Jean Francis Pinglot ◽  
Niels Gunuestrup
Keyword(s):  
Mass Balance ◽  
Accumulation Rate ◽  
Austral Summer ◽  
Katabatic Winds ◽  
Surface Gradient ◽  
Ice Stream ◽  
Dronning Maud Land ◽  
Temporal And Spatial ◽  
Accumulation Trend ◽  
Local Accumulation

A mass-balance programme was initiated on Jutulstraumen ice stream, western Dronning Maud Land,Antarctica, during the austral summer 1992-93. As a part of the mass-balance programme, accumulation rate was measured along the centre line of Jutulstraumen from the shelf edge up to the plateau at about 2500 m a.s.l. Accumulation distribution obtained from seven shallow firn cores and 48 slake readings is presented. The overall net accumulation trend displays a decreasing accumulation with increasing elevation and distance to coast, but on both the mesoscale and microscale there are significant variations. This is due to complex patterns of precipitation controlled by orography and redistribution by katabatic winds. The local accumulation distribution (few km scale) was found to be dependent on downslope surface gradient (aspect north, northwest), and variations up to 100% were found over distances of less than 3 km. The large variation in accumulation is important when selecting new core sites and for interpretation of temporal and spatial variations in accumulation derived from firn cores.

scholarly journals Changes in speed near the onset of Bindschadler Ice Stream, West Antarctica

2007 ◽  
Vol 46 ◽  
pp. 83-86 ◽  
Author(s):  
J. Paul Winberry ◽  
Sridhar Anandakrishnan ◽  
Andrew M. Smith
Keyword(s):  
Velocity Field ◽  
Mass Balance ◽  
Temporal Pattern ◽  
Ice Sheet ◽  
West Antarctica ◽  
Ice Stream ◽  
Ice Sheet Mass Balance ◽  
The Stability ◽  
Inland Ice ◽  
Onset Location

AbstractIce-stream velocities can change rapidly. Understanding the spatial and temporal pattern of these changes and the forcings responsible is essential for predicting ice-sheet mass balance. Inland migration of the onset location will lead to more efficient drainage of inland ice. One way to monitor the stability of the onset location is to investigate changes in the velocity field. We report on the velocity near the onset of Bindschadler Ice Stream, West Antarctica, in 2002 and compare these data to the velocity measured in 1996. Mean annual velocities were determined by measuring the GPS position of markers during consecutive seasons. We compare our results with similar measurements from 1996 to investigate temporal changes in this ice-stream onset. Our results indicate that only minimal changes have occurred in the speed of the ice stream between 1996 and 2002.

scholarly journals A time marker at 17.5 kyr BP detected throughout West Antarctica

2005 ◽  
Vol 41 ◽  
pp. 47-51 ◽  
Author(s):  
Robert W. Jacobel ◽  
Brian C. Welch
Keyword(s):  
Accumulation Rate ◽  
Ice Sheet ◽  
Weddell Sea ◽  
West Antarctica ◽  
Layer Depth ◽  
Time Marker ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
Ice Stream ◽  
Siple Dome

AbstractDeep radar soundings as part of the International Trans-Antarctic Scientific Expedition (US-ITASE) traverses in West Antarctica have revealed a bright internal reflector that we have imaged throughout widespread locations across the ice sheet. The layer is seen in traverses emanating from Byrd Station in four directions and has been traced continuously for distances of 535km toward the Weddell Sea drainage, 500km toward South Pole, 150km toward the Executive Committee Range and 160km toward Kamb Ice Stream (former Ice Stream C). The approximate area encompassed by the layer identified in these studies is 250 000km2. If the layer identification can also be extended to Siple Dome where we have additional radar soundings (Jacobel and others, 2000), the approximate area covered would increase by 50%. In many locations echo strength from the layer rivals the bed echo in amplitude even though it generally lies at a depth greater than half the ice thickness. At Byrd Station, where the layer depth is 1260 m, an age of ~17.5 kyr BP has been assigned based on the Blunier and Brook (2001) chronology. Hammer and others (1997) note that the acidity at this depth is >20 times the amplitude of any other part of the core. The depiction of this strong and widespread dated isochrone provides a unique time marker for much of the ice in West Antarctica. We apply a layer-tracing technique to infer the depth–time scale at the inland West Antarctic ice sheet divide and use this in a simple model to estimate the average accumulation rate.

scholarly journals The detailed net mass balance of the Ice plain on Ice Stream B, Antarctica: a geographic information system approach

1993 ◽  
Vol 39 (133) ◽  
pp. 471-482 ◽  
Author(s):  
Robert Bindschadler ◽  
Patricia L. Vornberger ◽  
Sion Shabtaie
Keyword(s):  
Information System ◽  
Geographic Information System ◽  
Mass Balance ◽  
System Approach ◽  
Field Data ◽  
Geographic Information ◽  
Ice Thickness ◽  
Spatial Averaging ◽  
Ice Stream ◽  
Ice Stream B

AbstractField data of ice thickness, velocity and accumulation of the ice plain region of Ice Stream B, Antarctica, are organized into a geographic information system (GIS) and used to calculate the spatial pattern of net mass balance. Overall, the ice plain is thickening at a rate of 0.13 ± 0.05 m a−1. Large uncertainties of the high-resolution calculations are reduced by spatial averaging, revealing a number of areas significantly out of balance. Ice in the broad diverging flow field is mostly thinning but a thinner region of the ice plain which includes ice raft “a” is thickening. Thickening is also indicated farther downstream on the ice plain, matching the thickening already calculated to be occurring upstream of Crary Ice Rise. The patterns of net mass balance for the two major tributaries of Ice Stream Β are asymmetric, demonstrating a real difference in the current dynamics of these two tributaries.

scholarly journals Delineation of a catchment boundary using velocity and elevation measurements

1998 ◽  
Vol 27 ◽  
pp. 140-144 ◽  
Author(s):  
S. F. Price ◽  
I. M. Whillans
Keyword(s):  
Field Measurements ◽  
Surface Velocity ◽  
Data Sampling ◽  
West Antarctica ◽  
Ice Surface ◽  
Ice Stream ◽  
Elevation Data ◽  
Boundary Location ◽  
Ice Stream B

The determination of catchment boundaries is a major source of uncertainty in net balance studies on large ice sheets. Here, a method for defining a catchment boundary is developed using new measurements of ice-surface velocity and elevation near the Ice Stream B/C boundary in West Antarctica. An objective method for estimating confidence in the catchment boundary is proposed. Using elevation data, the resulting mean standard deviation in boundary location is 13 km in position or 6000 km2 in area. Applying a similar uncertainty to both sides of the Ice Stream Β catchment results in a catchment-area uncertainty of 9%. Much larger uncertainties arise when the method is applied to velocity data. The uncertainty in both cases is primarily determined by the density of field measurements and is proportionally similar for larger catchment basins. Differences in the position of the velocity-determined boundary and the elevation-determined boundary probably result from data sampling. The boundary positions determined here do not support the hypothesis that Ice Stream Β captured parts of the Ice Stream C catchment.

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