Landform modification by palaeo-ice streams in east-central Ireland

AbstractIn eastern Ireland, subglacial bedforms including drumlins and Rogen moraines were modified by headward erosion along two ice streams which had overlapping flow tracks. The ice streams, which had tidewater termini, are dated by geochronometric and morphostratigraphic methods to <15.014 C kyr BP (Castleblaney ice stream) and ~13.814C kyr BP (Armagh ice stream). Bedforms along ice-stream tracks show a morphological continuum which reflects a down-ice increase in the degree of modification by ice-stream activity (i.e. resulting in unmodified →remoulded/overprinted →crosscut →streamlined bedforms). The down-ice changes in bedform types are inferred to relate to changes in subglacial drainage and sediment-transport mechanisms. Bedform and sedimentary evidence suggest that discrete subglacial meltwater channels which developed up- ice changed in a down-ice direction to unchannelized flows which deepened towards the ice margin. Meltwater release from subglacial cavities, and produced by strain heating at sheared ice-stream margins, probably helped support ice-stream flow, which ended as the volume of subglacial meltwater discharge decreased. Dated millennial-scale cycles of ice activity may be related to instability at tidewater margins, followed by complex thermal and hydraulic responses within the ice mass.

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Is Ice-Stream Evolution Revealed By Satellite Imagery?

Annals of Glaciology ◽

10.3189/s0260305500008740 ◽

1990 ◽

Vol 14 ◽

pp. 273-277 ◽

Cited By ~ 5

Author(s):

S.N. Stephenson ◽

R.A. Bindschadler

Keyword(s):

Stream Flow ◽

Temporal Evolution ◽

Thematic Mapper ◽

Landsat Thematic Mapper ◽

West Antarctica ◽

Ice Streams ◽

Ice Flow ◽

Ice Shelves ◽

Ice Stream ◽

Grounding Line

Ten Landsat Thematic Mapper images together show Ice Streams E, D and most of Ice Stream C on Siple Coast, West Antarctica. The images are interpreted to reveal aspects of both spatial and temporal evolution of the ice streams. Onset of ice-stream flow appears to occur at distributed sites within the ice-stream catchment, and the apparent enhanced flow continues in channels until they join, forming the main ice stream. Most crevassing on these ice streams is associated with features of horizontal dimensions between 5 and 20 km. We suggest these features are caused by bed structures which may be an important source of restraint to ice flow, similar to ice rumples on ice shelves. A pattern of features near the grounding line of the now-stagnant Ice Stream C are interpreted as having formed because there was a period of reduced flux before the ice stream stopped.

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Is Ice-Stream Evolution Revealed By Satellite Imagery?

Annals of Glaciology ◽

10.1017/s0260305500008740 ◽

1990 ◽

Vol 14 ◽

pp. 273-277 ◽

Cited By ~ 28

Author(s):

S.N. Stephenson ◽

R.A. Bindschadler

Keyword(s):

Stream Flow ◽

Temporal Evolution ◽

Thematic Mapper ◽

Landsat Thematic Mapper ◽

West Antarctica ◽

Ice Streams ◽

Ice Flow ◽

Ice Shelves ◽

Ice Stream ◽

Grounding Line

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Tributaries to West Antarctic ice streams: characteristics deduced from numerical modelling of ice flow

Annals of Glaciology ◽

10.3189/172756400781819969 ◽

2000 ◽

Vol 31 ◽

pp. 184-190 ◽

Cited By ~ 18

Author(s):

Christina L. Hulbe ◽

Ian R. Joughin ◽

David L. Morse ◽

Robert A. Bindschadler

Keyword(s):

Numerical Modelling ◽

Stream Flow ◽

Water Storage ◽

Consistent Pattern ◽

Ice Thickness ◽

Ice Streams ◽

The West ◽

Ice Flow ◽

West Antarctic ◽

Ice Stream

AbstractA network of relatively fast-flowing tributaries in the catchment basins of the West Antarctic ice streams transport ice from the inland reservoir to the heads of the ice streams. Branches of the network follow valleys in basal topography but not all valleys contain tributaries. We investigate the circumstances favoring tributary flow upstream of Ice Streams D and E, using a combination of observation and numerical modelling. No consistent pattern emerges. The transition from tributary to ice-stream flow occurs smoothly along the main tributary feeding into the onset of Ice Stream D, with ice thickness being relatively more important upstream, and sliding being relatively more important downstream. Elsewhere, the downstream pattern of flow is more complicated, with local increases and decreases in the contribution of sliding to ice speed. Those changes may be due to variations in basal water storage, subglacial geologic properties or a combination of the two.

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Melting and freezing beneath the Ross ice streams, Antarctica

Journal of Glaciology ◽

10.3189/172756504781830295 ◽

2004 ◽

Vol 50 (168) ◽

pp. 96-108 ◽

Cited By ~ 75

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.

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Ribbed bedforms on palaeo-ice stream beds resemble regular patterns of basal shear stress (‘traction ribs’) inferred from modern ice streams

Journal of Glaciology ◽

10.1017/jog.2016.63 ◽

2016 ◽

Vol 62 (234) ◽

pp. 696-713 ◽

Cited By ~ 9

Author(s):

CHRIS R. STOKES ◽

MARTIN MARGOLD ◽

TIMOTHY T. CREYTS

Keyword(s):

Shear Stress ◽

Ice Sheets ◽

Western Canada ◽

Coupled Flow ◽

Ice Streams ◽

Ice Stream ◽

Stream Beds ◽

Basal Shear ◽

Subglacial Meltwater ◽

Regular Patterns

Rapidly-flowing ice streams are an important mechanism through which ice sheets lose mass, and much work has been focussed on elucidating the processes that increase or decrease their velocity. Recent work using standard inverse methods has inferred previously-unrecognised regular patterns of high basal shear stress (‘sticky spots’ >200 kPa) beneath a number of ice streams in Antarctica and Greenland, termed ‘traction ribs’. They appear at a scale intermediate between smaller ribbed moraines and much larger mega-ribs observed on palaeo-ice sheet beds, but it is unclear whether they have a topographic expression at the bed. Here, we report observations of rib-like bedforms from DEMs along palaeo-ice stream beds in western Canada that resemble both the pattern and dimensions of traction ribs. Their identification suggests that traction ribs may have a topographic expression that lies between, and partly overlaps with, ribbed moraines and much larger mega-ribs. These intermediate-sized bedforms support the notion of a ribbed bedform continuum. Their formation remains conjectural, but our observations from palaeo-ice streams, coupled with those from modern ice masses, suggest they are related to wave-like instabilities occurring in the coupled flow of ice and till and modulated by subglacial meltwater drainage. Their form and pattern may also involve glaciotectonism of subglacial sediments.

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

The Cryosphere Discussions ◽

10.5194/tcd-6-4267-2012 ◽

2012 ◽

Vol 6 (5) ◽

pp. 4267-4304 ◽

Cited By ~ 2

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.

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Ice-stream flow switching by up-ice propagation of instabilities along glacial marginal troughs

The Cryosphere ◽

10.5194/tc-13-981-2019 ◽

2019 ◽

Vol 13 (3) ◽

pp. 981-996 ◽

Cited By ~ 2

Author(s):

Etienne Brouard ◽

Patrick Lajeunesse

Keyword(s):

Stream Flow ◽

Ice Sheets ◽

Ice Sheet ◽

Driving Mechanism ◽

Stream Networks ◽

Ice Streams ◽

Swath Bathymetry ◽

Ice Stream ◽

Global Sea Level ◽

Flow Switch

Abstract. Ice-stream networks constitute the arteries of ice sheets through which large volumes of glacial ice are rapidly delivered from the continent to the ocean. Modifications in ice-stream networks have a major impact on ice sheet mass balance and global sea level. Reorganizations in the drainage network of ice streams have been reported in both modern and paleo-ice sheets and usually result in ice streams switching their trajectory and/or shutting down. While some hypotheses for the reorganization of ice streams have been proposed, the mechanisms that control the switching of ice streams remain poorly understood and documented. Here, we interpret a flow switch in an ice-stream system that occurred prior to the last glaciation on the northeastern Baffin Island shelf (Arctic Canada) through glacial erosion of a marginal trough, i.e., deep parallel-to-coast bedrock moats located up-ice of a cross-shelf trough. Shelf geomorphology imaged by high-resolution swath bathymetry and seismo-stratigraphic data in the area indicate the extension of ice streams from Scott and Hecla & Griper troughs towards the interior of the Laurentide Ice Sheet. Up-ice propagation of ice streams through a marginal trough is interpreted to have led to the piracy of the neighboring ice catchment that in turn induced an adjacent ice-stream flow switch and shutdown. These results suggest that competition for ice discharge between the two ice streams, which implies piracy of ice drainage basins via marginal troughs, was the driving mechanism behind ice flow switching. In turn, the enlargement of the ice catchment by piracy increased the volume and discharge of Scott Ice Stream, allowing it to erode deeper and flow farther on the continental shelf. Similar trough systems observed on many other glaciated continental shelves may be the product of such competition for ice discharge between catchments.

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New and improved determinations of velocity of Ice Streams B and C, West Antarctica

Journal of Glaciology ◽

10.3189/s0022143000016373 ◽

1993 ◽

Vol 39 (133) ◽

pp. 483-590 ◽

Cited By ~ 6

Author(s):

I. M. Whillans ◽

C.J. Van Der Veen

Keyword(s):

Stream Flow ◽

West Antarctica ◽

Ice Shelf ◽

Ice Streams ◽

Ice Flow ◽

Ice Stream ◽

Fast Ice ◽

Ice Stream B ◽

Shelf Flow ◽

Streaming Flow

AbstractMeasurements of velocity have been made on and next to Ice Streams Β and C, West Antarctica. The results are more precise than previous work and constitute a 93% increase in the number of values. These velocities are used to describe the confluence of flow into the ice streams and the development of fast ice-stream flow. The onset of fast-streaming flow occurs in many separate tributaries that coalesce down-glacier into the major ice streams. For those inter-stream ridges that have been studied, the flow is consistent with steady state. Along Ice Stream B, gradients in longitudinal stress offer little resistance to the ice flow. The transition from basal-drag control to ice-shelf flow is achieved through reduced drag at the glacier base and increased resistance associated with lateral drag. Velocities in the trunk of Ice Stream C are nearly zero but those at the up-glacial head are similar to those at the head of Ice Stream B.

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New and improved determinations of velocity of Ice Streams B and C, West Antarctica

Journal of Glaciology ◽

10.1017/s0022143000016373 ◽

1993 ◽

Vol 39 (133) ◽

pp. 483-590 ◽

Cited By ~ 87

Author(s):

I. M. Whillans ◽

C.J. Van Der Veen

Keyword(s):

Stream Flow ◽

West Antarctica ◽

Ice Shelf ◽

Ice Streams ◽

Ice Flow ◽

Ice Stream ◽

Fast Ice ◽

Ice Stream B ◽

Shelf Flow ◽

Streaming Flow

Abstract Measurements of velocity have been made on and next to Ice Streams Β and C, West Antarctica. The results are more precise than previous work and constitute a 93% increase in the number of values. These velocities are used to describe the confluence of flow into the ice streams and the development of fast ice-stream flow. The onset of fast-streaming flow occurs in many separate tributaries that coalesce down-glacier into the major ice streams. For those inter-stream ridges that have been studied, the flow is consistent with steady state. Along Ice Stream B, gradients in longitudinal stress offer little resistance to the ice flow. The transition from basal-drag control to ice-shelf flow is achieved through reduced drag at the glacier base and increased resistance associated with lateral drag. Velocities in the trunk of Ice Stream C are nearly zero but those at the up-glacial head are similar to those at the head of Ice Stream B.

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Stress balances of ice streams in a vertically integrated, higher-order formulation

Journal of Glaciology ◽

10.3189/2013jog12j140 ◽

2013 ◽

Vol 59 (215) ◽

pp. 449-466 ◽

Cited By ~ 6

Author(s):

T.M. Kyrke-Smith ◽

R.F. Katz ◽

A.C. Fowler

Keyword(s):

Stream Flow ◽

Numerical Solutions ◽

Ice Sheet ◽

Higher Order ◽

Ice Streams ◽

Margin Width ◽

Ice Stream ◽

Internal Deformation ◽

Slow Moving ◽

Ice Sheet Dynamics

AbstractOne challenge in improving our understanding of ice-stream dynamics is to develop models of the spatial and temporal transition from ice-sheet to ice-stream flow. We address this with a new, vertically integrated, higher-order formulation for ice-sheet dynamics that captures the leading-order physics of low aspect ratio, viscous fluid flow, regardless of the amount of slip at the bed. The theory introduces a parameter, λ, which approximates the ratio of the basal stress to the shear stress scale, providing a measure of the relative importance of sliding and internal deformation. Our model is able to simultaneously describe the dynamics of both a slow-moving sheet and rapidly flowing ice streams. To test the formulation, we apply a triple-valued sliding law as the basal boundary condition and obtain numerical solutions that can be compared with previous work. We investigate the sensitivity of flow regimes and shear margin width to parameter variation, deriving a scaling for the latter. We also consider a double-valued sliding law, which enforces a constant, low basal stress beneath the ice stream. Comparisons of the resultant stress fields illustrate the different stress balances that can maintain ice-stream flow.

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