scholarly journals The Dynamics of Ice-Sheet Outlets

1985 ◽  
Vol 31 (108) ◽  
pp. 99-107 ◽  
Author(s):  
N. F. Mcintyre
Keyword(s):  
Landsat Imagery ◽  
Ice Sheet ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Shelves ◽  
Surface Slopes ◽  
Basal Sliding ◽  
Subglacial Topography ◽  
Flow Through ◽  
Pressure Melting

AbstractA comparison of data from aircraft altimetry, Landsat imagery, and radia echo-sounding has shown characteristic surface topographies associated with sheet and stream flow. The transition between the two is abrupt and occurs at a step in the subglacial topography. This marks the onset of basal sliding and high velocities caused by subglacial water; it results in crevassed amphitheatre-like basins round the head of outlet glaciers. It is also the zone of maximum driving stress beyond which values decline rapidly as velocities increase. This abrupt transition appears to be topographically controlled since basal temperatures are at the pressure-melting point well inland of the change in regime. The Marie Byrd Land ice streams exhibit qualitative differences from other ice-sheet outlets, however; the change to lower driving stresses is much more gradual and occurs several hundred kilometres inland. Such ice streams have particularly low surface slopes and appear in form and flow regime to resemble confined ice shelves rather than grounded ice. The repeated association of the transition to rapid sliding with a distinct subglacial feature implies a stabilizing effect on discharge through outlet glaciers. Acceleration of the ice is pinned to a subglacial step and propagation of high velocities inland of this feature seems improbable. Rapid ice flow through subglacial trenches may also ensure a relatively permanent trough through accentuation of the feature by erosion. This is concentrated towards the heads of outlet glaciers up-stream of the region where significant basal decoupling occurs. This may be a mechanism for the overdeepening of fjords at their inland ends and the development of very steep fjord headwalls.

scholarly journals The Dynamics of Ice-Sheet Outlets

1985 ◽  
Vol 31 (108) ◽  
pp. 99-107 ◽  
Author(s):  
N. F. Mcintyre
Keyword(s):  
Landsat Imagery ◽  
Ice Sheet ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Shelves ◽  
Surface Slopes ◽  
Basal Sliding ◽  
Subglacial Topography ◽  
Flow Through ◽  
Pressure Melting

AbstractA comparison of data from aircraft altimetry, Landsat imagery, and radia echo-sounding has shown characteristic surface topographies associated with sheet and stream flow. The transition between the two is abrupt and occurs at a step in the subglacial topography. This marks the onset of basal sliding and high velocities caused by subglacial water; it results in crevassed amphitheatre-like basins round the head of outlet glaciers. It is also the zone of maximum driving stress beyond which values decline rapidly as velocities increase. This abrupt transition appears to be topographically controlled since basal temperatures are at the pressure-melting point well inland of the change in regime. The Marie Byrd Land ice streams exhibit qualitative differences from other ice-sheet outlets, however; the change to lower driving stresses is much more gradual and occurs several hundred kilometres inland. Such ice streams have particularly low surface slopes and appear in form and flow regime to resemble confined ice shelves rather than grounded ice. The repeated association of the transition to rapid sliding with a distinct subglacial feature implies a stabilizing effect on discharge through outlet glaciers. Acceleration of the ice is pinned to a subglacial step and propagation of high velocities inland of this feature seems improbable. Rapid ice flow through subglacial trenches may also ensure a relatively permanent trough through accentuation of the feature by erosion. This is concentrated towards the heads of outlet glaciers up-stream of the region where significant basal decoupling occurs. This may be a mechanism for the overdeepening of fjords at their inland ends and the development of very steep fjord headwalls.

scholarly journals Objective Reconstructions of the Late Wisconsinan Laurentide Ice Sheet and the Significance of Deformable Beds

2007 ◽  
Vol 39 (3) ◽  
pp. 229-238 ◽  
Author(s):  
D. A. Fisher ◽  
N. Reeh ◽  
K. Langley
Keyword(s):  
Yield Stress ◽  
Flow Direction ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Hudson Bay ◽  
Ice Streams ◽  
Ice Flow ◽  
Surface Slopes ◽  
Late Wisconsinan

ABSTRACT A three dimensional steady state plastic ice model; the present surface topography (on a 50 km grid); a recent concensus of the Late Wisconsinan maximum margin (PREST, 1984); and a simple map of ice yield stress are used to model the Laurentide Ice Sheet. A multi-domed, asymmetric reconstruction is computed without prior assumptions about flow lines. The effects of possible deforming beds are modelled by using the very low yield stress values suggested by MATHEWS (1974). Because of low yield stress (deforming beds) the model generates thin ice on the Prairies, Great Lakes area and, in one case, over Hudson Bay. Introduction of low yield stress (deformabie) regions also produces low surface slopes and abrupt ice flow direction changes. In certain circumstances large ice streams are generated along the boundaries between normal yield stress (non-deformable beds) and low yield stress ice (deformabie beds). Computer models are discussed in reference to the geologically-based reconstructions of SHILTS (1980) and DYKE ef al. (1982).

scholarly journals Description of a hybrid ice sheet-shelf model, and application to Antarctica

2012 ◽  
Vol 5 (5) ◽  
pp. 1273-1295 ◽  
Author(s):  
D. Pollard ◽  
R. M. DeConto
Keyword(s):  
Ice Sheet ◽  
Last Deglaciation ◽  
Ice Flow ◽  
Ice Shelves ◽  
Continental Scale ◽  
Hybrid Combination ◽  
Grounding Line ◽  
Basal Sliding ◽  
The Last Deglaciation

Abstract. The formulation of a 3-D ice sheet-shelf model is described. The model is designed for long-term continental-scale applications, and has been used mostly in paleoclimatic studies. It uses a hybrid combination of the scaled shallow ice and shallow shelf approximations for ice flow. Floating ice shelves and grounding-line migration are included, with parameterized ice fluxes at grounding lines that allows relatively coarse resolutions to be used. All significant components and parameterizations of the model are described in some detail. Basic results for modern Antarctica are compared with observations, and simulations over the last 5 million years are compared with previously published results. The sensitivity of ice volumes during the last deglaciation to basal sliding coefficients is discussed.

scholarly journals Fracture-induced softening for large-scale ice dynamics

2013 ◽  
Vol 7 (5) ◽  
pp. 4501-4544 ◽  
Author(s):  
T. Albrecht ◽  
A. Levermann
Keyword(s):  
Large Scale ◽  
Ice Sheet ◽  
Damage Threshold ◽  
Fracture Density ◽  
Ice Streams ◽  
Model Framework ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Ice Shelves ◽  
Linear Threshold

Abstract. Floating ice shelves can exert a retentive and hence stabilizing force onto the inland ice sheet of Antarctica. However, this effect has been observed to diminish by fracture-coupled dynamic processes within the protective ice shelves leading to accelerated ice flow and hence to a sea-level contribution. In order to better understand the role of fractures in ice dynamics we apply a large-scale continuum representation of fractures and related fracture growth into the prognostic Parallel Ice Sheet Model (PISM). To this end we introduce a higher-order accuracy advection scheme for the transport of the two-dimensional fracture density across the regular computational grid. Dynamic coupling of fractures and ice flow is attained by a reduction of effective ice viscosity proportional to the inferred fracture density. This formulation implies the possibility of a non-linear threshold behavior due to self-amplified fracturing in shear regions triggered by small variations in damage threshold. As a result of prognostic flow simulations, flow patterns with realistically large across-flow velocity gradients in fracture-weakened regions as seen in observations are reproduced. This model framework is expandable to grounded ice streams and accounts for climate-induced effects on fracturing and hence on the ice-flow dynamics. It further allows for an enhanced fracture-based calving parameterization.

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 Fracture-induced softening for large-scale ice dynamics

2014 ◽  
Vol 8 (2) ◽  
pp. 587-605 ◽  
Author(s):  
T. Albrecht ◽  
A. Levermann
Keyword(s):  
Large Scale ◽  
Ice Sheet ◽  
Fracture Initiation ◽  
Fracture Density ◽  
Ice Streams ◽  
Model Framework ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Ice Shelves ◽  
Fracture Processes

Abstract. Floating ice shelves can exert a retentive and hence stabilizing force onto the inland ice sheet of Antarctica. However, this effect has been observed to diminish by the dynamic effects of fracture processes within the protective ice shelves, leading to accelerated ice flow and hence to a sea-level contribution. In order to account for the macroscopic effect of fracture processes on large-scale viscous ice dynamics (i.e., ice-shelf scale) we apply a continuum representation of fractures and related fracture growth into the prognostic Parallel Ice Sheet Model (PISM) and compare the results to observations. To this end we introduce a higher order accuracy advection scheme for the transport of the two-dimensional fracture density across the regular computational grid. Dynamic coupling of fractures and ice flow is attained by a reduction of effective ice viscosity proportional to the inferred fracture density. This formulation implies the possibility of non-linear threshold behavior due to self-amplified fracturing in shear regions triggered by small variations in the fracture-initiation threshold. As a result of prognostic flow simulations, sharp across-flow velocity gradients appear in fracture-weakened regions. These modeled gradients compare well in magnitude and location with those in observed flow patterns. This model framework is in principle expandable to grounded ice streams and provides simple means of investigating climate-induced effects on fracturing (e.g., hydro fracturing) and hence on the ice flow. It further constitutes a physically sound basis for an enhanced fracture-based calving parameterization.

scholarly journals Results of the third Marine Ice Sheet Model Intercomparison Project (MISMIP+)

2020 ◽  
Author(s):  
Stephen L. Cornford ◽  
Helene Seroussi ◽  
Xylar S. Asay-Davis ◽  
G. Hilmar Gudmundsson ◽  
Rob Arthern ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Stable Steady State ◽  
Ice Streams ◽  
Important Distinction ◽  
Ice Flow ◽  
Ice Shelves ◽  
Flow Models ◽  
The Third ◽  
Intercomparison Project ◽  
The Difference

Abstract. We present the result of the third Marine Ice Sheet Intercomparison project, MISMIP+. MISMIP+ is intended to be a test of ice flow models which include fast sliding marine ice streams and floating ice shelves and in particular a treatment of viscous stress that is sufficient for buttressing, where upstream ice flow is restrained by a downstream ice shelf. A set of idealized experiments test the models in circumstances where buttressing contributes to a stable steady state, and where a reduction in that buttressing causes ice stream acceleration, thinning, and grounding line retreat. We find that the most important distinction between models in this particular type of simulation is in the treatment of sliding at the bed, with other distinctions – notably the difference between the simpler and more complete treatments of englacial stress, but also the differences between numerical methods – taking a secondary role.

scholarly journals Description of a hybrid ice sheet-shelf model, and application to Antarctica

2012 ◽  
Vol 5 (2) ◽  
pp. 1077-1134 ◽  
Author(s):  
D. Pollard ◽  
R. M. DeConto
Keyword(s):  
Ice Sheet ◽  
Last Deglaciation ◽  
Ice Flow ◽  
Ice Shelves ◽  
Continental Scale ◽  
Grounding Line ◽  
Basal Sliding ◽  
Ice Retreat ◽  
The Last Deglaciation

Abstract. The formulation of a 3-D ice sheet-shelf model is described. The model is designed for long-term continental-scale applications, and has been used mostly in paleoclimatic studies. It uses a hybrid combination of the scaled Shallow Ice and Shallow Shelf Approximations for ice flow. Floating ice shelves and grounding-line migration are included, with parameterized ice fluxes at grounding lines that allows relatively coarse resolutions to be used. All significant components and parameterizations of the model are described in some detail. Basic results for modern Antarctica are compared with observations, and simulations over the last 5 million yr are shown to be similar to previously published results using an earlier model version. The sensitivity of ice retreat during the last deglaciation to basal sliding coefficients is discussed.

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