scholarly journals Basal conditions and ice dynamics inferred from radar-derived internal stratigraphy of the northeast Greenland ice stream

2014 ◽  
Vol 55 (67) ◽  
pp. 127-137 ◽  
Author(s):  
Benjamin A. Keisling ◽  
Knut Christianson ◽  
Richard B. Alley ◽  
Leo E. Peters ◽  
John E.M. Christian ◽  
...  
Keyword(s):  
Steady State ◽  
Additional Data ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Ice Stream ◽  
Radio Echo Sounding ◽  
Ice Flows ◽  
Basal Melting ◽  
Spatially Varying ◽  
Geothermal Flux

AbstractWe analyze the internal stratigraphy in radio-echo sounding data of the northeast Greenland ice stream to infer past and present ice dynamics. In the upper reaches of the ice stream, we propose that shear-margin steady-state folds in internal reflecting horizons (IRHs) form due to the influence of ice flow over spatially varying basal lubrication. IRHs are generally lower in the ice stream than outside, likely because of greater basal melting in the ice stream from enhanced geothermal flux and heat of sliding. Strain-rate modeling of IRHs deposited during the Holocene indicates no recent major changes in ice-stream vigor or extent in this region. Downstream of our survey, IRHs are disrupted as the ice flows into a prominent overdeepening. When combined with additional data from other studies, these data suggest that upstream portions of the ice stream are controlled by variations in basal lubrication whereas downstream portions are confined by basal topography.

Constraining ice shelf basalt melting rates from isochrone data

2021 ◽  
Author(s):  
Vjeran Visnjevic ◽  
Reinhard Drews ◽  
Clemens Schannwell ◽  
Inka Koch
Keyword(s):  
Ocean Circulation ◽  
Radar Data ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Ice Shelves ◽  
Inverse Approach ◽  
History Of ◽  
Forward And Inverse Modeling ◽  
Basal Melting

<p>Ice shelves buttress ice flow from the continent towards the ocean, and their disintegration results in increased ice discharge.  Ice-shelf evolution and integrity is influenced by surface accumulation, basal melting, and ice dynamics. We find signals of all of these processes imprinted in the ice-shelf stratigraphy that can be mapped using isochrones imaged with radar.</p><p>Our aim is to develop an inverse approach to infer ice shelf basal melt rates using radar isochrones as observational constraints. Here, we investigate the influence of basalt melt rates on the shape of isochrones using combined insights from both forward and inverse modeling. We use the 3D full Stokes model Elmer/Ice in our forward simulations, aiming to reproduce isochrone patterns observed in our data. Moreover we develop an inverse approach based on the shallow shelf approximating, aiming to constrain basal melt rates using isochronal radar data and surface velocities. Insights obtained from our simulations can also guide the collection of new radar data (e.g., profile lines along vs. across-flow) in a way that ambiguities in interpreting the ice-shelf stratigraphy can be minimized. Eventually, combining these approaches will enable us to better constrain the magnitude and history of basal melting, which will give valuable input for ocean circulation and sea level rise projections.</p>

scholarly journals Numerical modelling of the historic front variation and the future behaviour of the Pasterze glacier, Austria

1997 ◽  
Vol 24 ◽  
pp. 234-241 ◽  
Author(s):  
Z. Zuo ◽  
J. Oerlemans
Keyword(s):  
Steady State ◽  
Flow Model ◽  
Calibration Method ◽  
Climate Scenarios ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Steady State Condition ◽  
Ice Volume ◽  
Future Warming ◽  
Dynamic Calibration Method

An ice-flow model is used to simulate the front variations of the Pasterze glacier, Austria. The model deals explicitly with the ice flux from sub-streams and tributaries to the main ice stream. The dynamic calibration method adopted successfully calibrates the ice-flow model under a non-steady-state condition. Despite the complexity of the glacier geometry, the ice dynamics of the Pasterze are adequately simulated.Results of the sensitivity experiments suggest that the Pasterze glacier has been in a non-steady state most of the time and has a response time of 34–50 years.Projections of the behaviour of the Pasterze in the next 100 years are made under various climate scenarios. Results suggest that the Pasterze will undergo a substantial retreat if there is future warming. The glacier is likely to retreat 2–5 km by the year 2100. The ice volume could be reduced by 24–63% by the end of the 21st century.

scholarly journals Modeling of ice flow and internal layers along a flowline through Swiss Camp, West Greenland

2002 ◽  
Vol 34 ◽  
pp. 303-308 ◽  
Author(s):  
W. L. Wang ◽  
H. J. Zwally ◽  
W. Abdalati ◽  
S. Luo
Keyword(s):  
Steady State ◽  
Accumulation Rate ◽  
Greenland Ice Sheet ◽  
Shear Stresses ◽  
Internal Layers ◽  
Ice Flow ◽  
West Greenland ◽  
Rate Relationship ◽  
Radio Echo Sounding ◽  
Temperature Surface

AbstractAn anisotropic-ice flowline model is applied to a flowline through Swiss Camp (69.57° N, 49.28° W), West Greenland, to estimate the dates of internal layers detected by radio-echo sounding measurements. The effect of an anisotropic-ice fabric on ice flow is incorporated into the steady-state flowline model. The stress–strain-rate relationship for anisotropic ice is characterized by an enhancement factor based on the laboratory observations of ice deformation under combined compression and shear stresses. By using present-day data of accumulation rate, surface temperature, surface elevation and ice thickness along the flowline as model inputs, a very close agreement is found between the isochrones generated from the model and the observed internal layers with confirmed dates. The results indicate that this part of the Greenland ice sheet is primarily in steady state.

scholarly journals Subglacial hydrological networks in Antarctica and their impact on ice flow

2004 ◽  
Vol 39 ◽  
pp. 67-72 ◽  
Author(s):  
Frédérique Remy ◽  
Benoît Legresy
Keyword(s):  
Remote Sensing ◽  
Ice Flow ◽  
Elevation Data ◽  
Antarctic Continent ◽  
Satellite Radar ◽  
Basal Melting ◽  
The Antarctic ◽  
Satellite Radar Altimetry ◽  
East West ◽  
Geothermal Flux

AbstractDeep beneath the thick ice cover of the Antarctic continent there exist subglacial hydrological networks, within which basal meltwater can flow. In this paper, we use surface elevation data from European Remote-sensing Satellite radar altimetry to map these subglacial hydrological networks for the whole continent. We observe a confused pattern of subglacial systems, linking regions where basal melting takes place. In some regions, channels can be followed over some hundreds of kilometres. Some of these meet the ice-sheet margin, suggesting that meltwater can be transported all the way to the ocean. We observe an east–west gradient in the distribution of hydrological networks that could be explained by the geothermal flux pattern.

scholarly journals Basal Mass Balance Along a Flow Line on Ronne Ice Shelf, Antarctica (Abstract)

1988 ◽  
Vol 11 ◽  
pp. 201
Author(s):  
A. Jenkins ◽  
C.S.M. Doake
Keyword(s):  
Steady State ◽  
Mass Balance ◽  
Flow Line ◽  
Average Rate ◽  
Ice Shelf ◽  
Grounding Line ◽  
Radio Echo Sounding ◽  
State Models ◽  
Basal Melting ◽  
Echo Sounding

Recent glaciological work on Ronne Ice Shelf has focused on an assumed flow line which extends from Rutford Ice Stream grounding line to the ice front. Results from doppler satellite surveying and radio echo-sounding are used in kinematic calculations to determine the basal mass balance, assuming the flow line to be in a steady state. Models suggest that basal melting dominates over most of the flow line and is most pronounced at the extremities. In the region within 300 km of the grounding line and over the final 45 km before the ice front, at least 1 m/a on average must melt away to maintain the observed velocity and thickness profile. More gentle melting occurs over about half the remaining distance, but in a region between 130 and 300 km in from the ice front, basal freezing must occur at an average rate of about 0.1 m/a to maintain a steady state. The existence of a thin layer of saline ice underlying the ice shelf, which persists for a further 80 km down-stream before being melted away entirely, is consistent with the weak returns observed during both airborne and ground-based radio echo-sounding in this region.

scholarly journals Signature of ice streaming in Bjørnøyrenna, Polar North Atlantic, through the Pleistocene and implications for ice-stream dynamics

2009 ◽  
Vol 50 (52) ◽  
pp. 17-26 ◽  
Author(s):  
Karin Andreassen ◽  
Monica Winsborrow
Keyword(s):  
Barents Sea ◽  
Extensional Flow ◽  
Three Dimensional ◽  
Ice Streams ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Ice Stream ◽  
Geomorphic Features ◽  
Common Behaviour ◽  
Fast Flow

AbstractThe geomorphology of palaeo-ice-stream beds and the internal structure of underlying tills can provide important information about the subglacial conditions during periods of fast flow and quiescence. This paper presents observations from three-dimensional seismic data, revealing the geomorphology of buried beds of the Bjørnøyrenna (Bear Island Trough) ice stream, the main drainage outlet of the former Barents Sea ice sheet. Repeated changes in ice dynamics are inferred from the observed successions of geomorphic features. Megablocks, aligned in long chains parallel to inferred ice-stream flowlines, and forming dipping plates that are thrust one on top of another, are taken as evidence for conditions of compressive ice flow. Mega-scale glacial lineations (MSGL) and pull-apart of underlying sediment blocks suggest extensional flow. The observed pattern of megablocks and rafts overprinted by MSGL indicates a change in ice dynamics from a compressional to an extensional flow regime. Till stiffening, due to subglacial freezing, is the favoured mechanism for creating switches in sub-ice-stream conditions. The observed pattern of geomorphic features indicates that periods of slowdown or quiescence were commonly followed by reactivation and fast flow during several glaciations, suggesting that this may be a common behaviour of marine ice streams.

scholarly journals Glaciological advances made with interferometric synthetic aperture radar

2010 ◽  
Vol 56 (200) ◽  
pp. 1026-1042 ◽  
Author(s):  
Ian Joughin ◽  
Ben E. Smith ◽  
Waleed Abdalati
Keyword(s):  
Synthetic Aperture Radar ◽  
Flow Velocity ◽  
Synthetic Aperture ◽  
Interferometric Synthetic Aperture Radar ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Outlet Glacier ◽  
Mountain Glaciers ◽  
Ice Stream ◽  
Aperture Radar

AbstractSpaceborne interferometric synthetic aperture radar (InSAR) techniques for measuring ice flow velocity and topography have developed rapidly over the last decade and a half, revolutionizing the study of ice dynamics. Spaceborne interferometry has contributed to major progress in many areas of glaciological study by: providing the first comprehensive measurements of ice-stream flow velocity over the major outlets of Greenland and Antarctica; revealing that ice-stream and outlet-glacier flow can change rapidly (months to years); improving understanding of several ice-sheet and ice-shelf processes; providing velocity for flux-gate based mass-balance assessment; mapping flow of mountain glaciers; and capturing the geomorphic traces of past ice flow. We review the basic technique development, the measurement characteristics, and the extensive set of results yielded by these measurements.

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 Basal Mass Balance Along a Flow Line on Ronne Ice Shelf, Antarctica (Abstract)

1988 ◽  
Vol 11 ◽  
pp. 201-201
Author(s):  
A. Jenkins ◽  
C.S.M. Doake
Keyword(s):  
Steady State ◽  
Mass Balance ◽  
Flow Line ◽  
Average Rate ◽  
Ice Shelf ◽  
Grounding Line ◽  
Radio Echo Sounding ◽  
State Models ◽  
Basal Melting ◽  
Echo Sounding

Recent glaciological work on Ronne Ice Shelf has focused on an assumed flow line which extends from Rutford Ice Stream grounding line to the ice front. Results from doppler satellite surveying and radio echo-sounding are used in kinematic calculations to determine the basal mass balance, assuming the flow line to be in a steady state. Models suggest that basal melting dominates over most of the flow line and is most pronounced at the extremities. In the region within 300 km of the grounding line and over the final 45 km before the ice front, at least 1 m/a on average must melt away to maintain the observed velocity and thickness profile. More gentle melting occurs over about half the remaining distance, but in a region between 130 and 300 km in from the ice front, basal freezing must occur at an average rate of about 0.1 m/a to maintain a steady state. The existence of a thin layer of saline ice underlying the ice shelf, which persists for a further 80 km down-stream before being melted away entirely, is consistent with the weak returns observed during both airborne and ground-based radio echo-sounding in this region.

Englacial stratigraphy in Ellsworth Subglacial Highlands, West Antarctica

2021 ◽  
Author(s):  
Felipe Napoleoni ◽  
Neil Ross ◽  
Michael J. Bentley ◽  
Stewart S.R. Jamieson ◽  
Andrew M. Smith ◽  
...  
Keyword(s):  
Internal Structure ◽  
Ice Sheet ◽  
Glacial History ◽  
West Antarctica ◽  
Large Area ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Surface Mass ◽  
West Antarctic ◽  
Ice Stream

<p>Airborne ice-penetrating radar surveys around the Ellsworth Subglacial Highlands (ESH) have mapped and dated englacial ice sheet layers, hereafter referred to as ‘Internal Reflection Horizons’ (IRHs). The geometry and internal structure of IRHs can reveal the cumulative effects of surface mass balance, strain, basal melt and ice dynamics, to improve understanding of the glacial history of West Antarctic Ice Sheet (WAIS). Despite the airborne-surveyed IRHs however, international efforts to develop a continental-wide scale coverage of IRHs (i.e. AntArchitecture), are limited by a lack of data in the critical regions between the upper reach of Pine Island Glacier (PIG), Rutford Ice Stream (RIS) and Institute Ice Stream (IIS). This region is important because any significant collapse of WAIS or reorganisation of ice flow would likely be felt in the ESH because it hosts deep subglacial troughs (Ellsworth Trough and CECs Trough), that represent a potential connection between the Weddell and Amundsen Seas. Using an extensive ground-based ice radar dataset acquired by Centro de Estudios Científicos (CECs) we bridge this regional gap by mapping IRHs across the Amundsen-Weddell divide of the WAIS. This work links airborne-derived IRH datasets across PIG and IIS, to develop an extensive layer characterisation across a large area of West Antarctica. We present the regional internal structure of the ice sheet, gridded paleo ice surfaces, and identify areas with complex IRH structures, and evaluate the possible glaciological processes responsible. We then compare our results with modelled outputs of ice sheet geometry and outline our current understanding of the past ice flow behaviour of the ESH, and the implications for WAIS glacial history. We consider our results in the context of the characterisation of ‘old-ice’ in WAIS and in relation to the upcoming plans for accessing subglacial Lake CECs in order to determine its history.</p>

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