scholarly journals The elevation history of ice streams and the spatial accumulation pattern along the Siple Coast of West Antarctica inferred from ground-based radar data from three inter-ice-stream ridges

2001 ◽  
Vol 47 (157) ◽  
pp. 303-313 ◽  
Author(s):  
N. A. Nereson ◽  
C. F. Raymond
Keyword(s):  
Spatial Pattern ◽  
Internal Layer ◽  
Windward Side ◽  
West Antarctica ◽  
Ice Streams ◽  
Amundsen Sea ◽  
The Past ◽  
Ice Stream ◽  
Siple Dome ◽  
History Of

AbstractMeasurements of the surface and internal layer geometry from ice-penetrating radar and global positioning system surveys on three inter-ice-stream ridges in West Antarctica (Siple Dome, ridge DE and ridge BC) are examined with ice-flow models to infer (1) the history of the divide position at each site and (2) the spatial pattern of accumulation across the ridges. We find that the divide position is most steady at Siple Dome, somewhat steady at ridge DE and highly variable at ridge BC. Data from Siple Dome and ridge DE show evidence for steady northward motion of the ice divide for the past few thousand years. The layers beneath ridge BC suggest a 5 km northward shift of the divide position within the past several hundred years. Assuming the divide shifts are all due to changing elevation of the bounding ice streams, we infer the relative elevation history for segments of Ice Streams B–E. The northward displacement of the divide for all ridges implies a progressive relative thinning of the ice streams from E to B, with most dramatic recent thinning (100 m in <103 years) of Ice Stream B relative to Ice Stream C. Analysis of the internal layer pattern across the ridges indicates a south–north accumulation gradient with higher accumulation rates on the northern flanks of the ridges in all three cases. The inferred accumulation distribution is nearly uniform on the northern flanks, decreases sharply within a few ice thicknesses across the divides, and then decreases gradually farther to the south. The north/south decrease is strongest for ridge DE and weakest for ridge BC. This spatial pattern and the reduction in gradient strength with distance from the Amundsen Sea is consistent with the hypothesis that storms from the Amundsen Sea carry moisture first south then west over West Antarctica and deposit more snow on the windward side of ridges due to orographic lifting. This pattern has been stable for at least the past several thousand years.

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.

scholarly journals Sensitivity of the divide position at Siple Dome, West Antarctica, to boundary forcing

1998 ◽  
Vol 27 ◽  
pp. 207-214 ◽  
Author(s):  
N. A. Nereson ◽  
R. C. A. Hindmarsh ◽  
C. F. Raymond
Keyword(s):  
Time Scales ◽  
Steady Increase ◽  
West Antarctica ◽  
Ice Streams ◽  
Accumulation Pattern ◽  
The Past ◽  
Ice Stream ◽  
Siple Dome ◽  
Climate Event ◽  
Short Time

A linearized perturbation about a two-dimensional Vialov-Nyc ice-shect profile is used to investigate the sensitivity of the divide position at Siple Dome, West Antarctica, to small changes in the accumulation pattern and in the elevation of its lateral boundaries at the margins of Ice Streams C and D. Relaxation time-scales for the ice-sheet surface and divide position are derived from the perturbation theory. For Siple Dome, these time-scales are short: 450 800 years for surface adjustment, and 200-350 years for divide position adjustment. These short time-scales indicate that Siple Dome responds quickly to forcing at its boundaries. Therefore, the recent migration of the Siple Dome divide (determined from previous work) is probably a response to an ongoing, sustained forcing rather than a response to a long-past climate event such as the transition from the Last Glacial Maximum to the Holocene. Based on our analysis, the inferred rate of migration of the Siple Dome divide could be attained by: (1) a steady increase in the south north spatial accumulation gradient of 0.1-1.5 × 10−9 a −2, or (2) a steady increase (decrease) in elevation of the Siple Dome lateral boundary adjacent to a relict margin of Ice Stream D (Ice Stream C) of 0.005-0.040 m a−1 over the past several thousand years. The required forcing is quite small, and suggests that major changes in the configuration of Ice Streams C and D associated with major changes in the elevation at boundaries of Siple Dome have not occurred over the past several thousand years.

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−1toward 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 10−6a−1in 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 103-104years.

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

2011 ◽  
Vol 5 (4) ◽  
pp. 907-916 ◽  
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.

scholarly journals Paleo ice flow and subglacial meltwater dynamics in Pine Island Bay, West Antarctica

2012 ◽  
Vol 6 (5) ◽  
pp. 4267-4304 ◽  
Author(s):  
F. O. Nitsche ◽  
K. Gohl ◽  
R. Larter ◽  
C.-D. Hillenbrand ◽  
G. Kuhn ◽  
...  
Keyword(s):  
West Antarctica ◽  
Ice Streams ◽  
Channel Network ◽  
Amundsen Sea ◽  
Ice Flow ◽  
Swath Bathymetry ◽  
Ice Stream ◽  
Seabed Topography ◽  
Ice Sheet Dynamics ◽  
Subglacial Meltwater

Abstract. Increasing evidence for an elaborate subglacial drainage network underneath modern Antarctic ice sheets suggests that basal meltwater has an important influence on ice stream flow. Swath bathymetry surveys from previously glaciated continental margins display morphological features indicative of subglacial meltwater flow in inner shelf areas of some paleo ice stream troughs. Over the last few years several expeditions to the Eastern Amundsen Sea embayment (West Antarctica) have investigated the paleo ice streams that extended from the Pine Island and Thwaites glaciers. A compilation of high-resolution swath bathymetry data from inner Pine Island Bay reveals details of a rough seabed topography including several deep channels that connect a series of basins. This complex basin and channel network is indicative of meltwater flow beneath the paleo-Pine Island and Thwaites ice streams, along with substantial subglacial water inflow from the east. This meltwater could have enhanced ice flow over the rough bedrock topography. Meltwater features diminish with the onset of linear features north of the basins. Similar features have previously been observed in several other areas, including the Dotson-Getz Trough (Western Amundsen Sea embayment) and Marguerite Bay (SW Antarctic Peninsula), suggesting that these features may be widespread around the Antarctic margin and that subglacial meltwater drainage played a major role in past ice-sheet dynamics.

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 Paleo ice flow and subglacial meltwater dynamics in Pine Island Bay, West Antarctica

2013 ◽  
Vol 7 (1) ◽  
pp. 249-262 ◽  
Author(s):  
F. O. Nitsche ◽  
K. Gohl ◽  
R. D. Larter ◽  
C.-D. Hillenbrand ◽  
G. Kuhn ◽  
...  
Keyword(s):  
West Antarctica ◽  
Ice Streams ◽  
Channel Network ◽  
Amundsen Sea ◽  
Ice Flow ◽  
Swath Bathymetry ◽  
Ice Stream ◽  
Seabed Topography ◽  
Ice Sheet Dynamics ◽  
Subglacial Meltwater

Abstract. Increasing evidence for an elaborate subglacial drainage network underneath modern Antarctic ice sheets suggests that basal meltwater has an important influence on ice stream flow. Swath bathymetry surveys from previously glaciated continental margins display morphological features indicative of subglacial meltwater flow in inner shelf areas of some paleo ice stream troughs. Over the last few years several expeditions to the eastern Amundsen Sea embayment (West Antarctica) have investigated the paleo ice streams that extended from the Pine Island and Thwaites glaciers. A compilation of high-resolution swath bathymetry data from inner Pine Island Bay reveals details of a rough seabed topography including several deep channels that connect a series of basins. This complex basin and channel network is indicative of meltwater flow beneath the paleo-Pine Island and Thwaites ice streams, along with substantial subglacial water inflow from the east. This meltwater could have enhanced ice flow over the rough bedrock topography. Meltwater features diminish with the onset of linear features north of the basins. Similar features have previously been observed in several other areas, including the Dotson-Getz Trough (western Amundsen Sea embayment) and Marguerite Bay (SW Antarctic Peninsula), suggesting that these features may be widespread around the Antarctic margin and that subglacial meltwater drainage played a major role in past ice-sheet dynamics.

scholarly journals The accumulation pattern across Siple Dome, West Antarctica, inferred from radar-detected internal layers

2000 ◽  
Vol 46 (152) ◽  
pp. 75-87 ◽  
Author(s):  
N. A. Nereson ◽  
C. F. Raymond ◽  
R.W. Jacobel ◽  
E. D. Waddington
Keyword(s):  
Accumulation Rate ◽  
Small Time ◽  
Internal Layer ◽  
Internal Layers ◽  
West Antarctica ◽  
Ice Streams ◽  
Accumulation Pattern ◽  
The North ◽  
Siple Dome ◽  
Radio Echo Sounding

AbstractThe spatial distribution of accumulation across Siple Dome, West Antarctica, is determined from analysis of the shapes of internal layers detected by radio-echo sounding (RES) measurements. A range of assumed accumulation patterns is used in an ice-flow model to calculate a set of internal layer patterns. Inverse techniques are used to determine which assumed accumulation pattern produces a calculated internal layer pattern that best matches the shape of internal layers from RES measurements. All of the observed internal layer shapes at Siple Dome can be matched using a spatially asymmetric accumulation pattern which has been steady over time. Relative to the divide, the best-fitting accumulation pattern predicts 40% less accumulation 30 km from the divide on the south flank of Siple Dome and 15–40% more accumulation 30 km from the divide on the north flank. The data also allow the possibility for a small time variation of the pattern north of the divide. The mismatch between the calculated and the observed layer shapes is slightly reduced when the accumulation rate north of the divide is higher in the past (> 5kyr BP) than at present. Sensitivity tests show that the predicted change in the spatial accumulation pattern required to cause the slight Siple Dome divide migration (inferred from previous studies) would be detectable in the internal layer pattern if it persisted for > 2 kyr. Our analysis reveals no evidence that such a change has occurred, and the possible change in accumulation distribution allowed by the data is in the opposite sense. Therefore, it is unlikely that the Siple Dome divide migration has been caused by a temporal change in the spatial pattern of accumulation. This conclusion suggests the migration may be caused by elevation changes in Ice Streams C and D at the boundaries of Siple Dome.

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

2011 ◽  
Vol 5 (2) ◽  
pp. 1219-1238
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 years and that fast flow has not occurred there during that time period.

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.

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