scholarly journals Ice-stream demise dynamically conditioned by trough shape and bed strength

2019 ◽  
Vol 5 (4) ◽  
pp. eaau1380 ◽  
Author(s):  
Tom Bradwell ◽  
David Small ◽  
Derek Fabel ◽  
Rachel K. Smedley ◽  
Chris D. Clark ◽  
...  
Keyword(s):  
Stream Flow ◽  
Three Dimensional ◽  
Step Change ◽  
Ice Streams ◽  
Ice Shelves ◽  
Ice Stream ◽  
Grounding Line ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Ice sheet mass loss is currently dominated by fast-flowing glaciers (ice streams) terminating in the ocean as ice shelves and resting on beds below sea level. The factors controlling ice-stream flow and retreat over longer time scales (>100 years), especially the role of three-dimensional bed shape and bed strength, remain major uncertainties. We focus on a former ice stream where trough shape and bed substrate are known, or can be defined, to reconstruct ice-stream retreat history and grounding-line movements over 15 millennia since the Last Glacial Maximum. We identify a major behavioral step change around 18,500 to 16,000 years ago—out of tune with external forcing factors—associated with the collapse of floating ice sectors and rapid ice-front retreat. We attribute this step change to a marked geological transition from a soft/weak bed to a hard/strong bed coincident with a change in trough geometry. Both these factors conditioned and ultimately hastened ice-stream demise.

scholarly journals Is Ice-Stream Evolution Revealed By Satellite Imagery?

1990 ◽  
Vol 14 ◽  
pp. 273-277 ◽  
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.

scholarly journals Is Ice-Stream Evolution Revealed By Satellite Imagery?

1990 ◽  
Vol 14 ◽  
pp. 273-277 ◽  
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.

scholarly journals On the Disintegration of Ice Shelves: the Role of Thinning

1982 ◽  
Vol 3 ◽  
pp. 146-151 ◽  
Author(s):  
T. J. Hughes
Keyword(s):  
Weak Links ◽  
Ice Melting ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Shelves ◽  
Ross Ice Shelf ◽  
Tidal Pumping ◽  
Grounding Line ◽  
Converging Flow

It is proposed that an ice shelf disintegrates when its calving front retreats faster than its grounding line. This paper examines the role of ice thinning in grounding-line retreat. Thinning occurs as a result of creep spreading and ice melting. Thinning by creep is examined for the general regime of bending converging flow in an ice shelf lying in a confined embayment, and at the grounding lines of ice streams that supply the ice shelf and ice rises where the ice shelf is grounded on bedrock. Thinning by melting is examined at these grounding lines for tidal pumping and for descent of surface melt water into strandline crevasses, where concentrated melting is focused at the supposed weak links that connect the ice shelf to its embayment, its ice streams, and its ice rises. Applications are made to the Ross Ice Shelf.

Tidal Forcing as a Trigger of Arctic Ice Stream Deglaciation

2020 ◽  
Author(s):  
Jesse Velay-Vitow ◽  
Richard Peltier
Keyword(s):  
High Amplitude ◽  
The Arctic ◽  
Ice Streams ◽  
Last Glacial Period ◽  
Last Glacial ◽  
Isostatic Adjustment ◽  
Ice Stream ◽  
Grounding Line ◽  
Arctic Ice ◽  
The Last Glacial

<p>It has been established recently (Velay-Vitow, Peltier and Stuhne JGR-Oceans 2019) that a high amplitude M2 tide may have triggered and contributed to the forcing of the rapid deglaciations of the Hudson Strait ice stream, commonly referred to as Heinrich events, during the last glacial period. The required conditions for a tidally triggered marine terminating ice stream instability are an ice stream with a retrograde slope of the ice stream bed at the edge of an ice sheet and high amplitude tides coincidental with the grounding line. Two paleo ice streams in the Arctic, the Amundsen Gulf ice stream and the McClure ice stream may have been amenable to rapid deglaciation prior to and during Younger Dryas time, as these locations may have been characterized by the required bathymetric conditions. Additionally, it has been shown in Griffiths and Peltier (GRL 2008) that the Arctic was megatidal at last glacial maximum. We investigate the possibility that some combination of the previously mentioned ice streams were rendered unstable by high amplitude polar tides, and proceeded to rapidly deglaciate, disgorging icebergs and ice rafted debris into the Arctic ocean. We further examine the effect that these proposed ice stream instabilities would have had on the tidal regime in the Arctic, and, by the mechanism of glacial isostatic adjustment, upon the underlying Arctic bathymetry.</p>

scholarly journals Grounding-zone flow variability of Priestley Glacier, Antarctica, in a diurnal tidal regime

2021 ◽  
Author(s):  
Reinhard Drews ◽  
Christian Wild ◽  
Oliver Marsh ◽  
Wolfgang Rack ◽  
Todd Ehlers ◽  
...  
Keyword(s):  
Spatial Scales ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Shelves ◽  
Ice Stream ◽  
Grounding Line ◽  
Temporal And Spatial ◽  
Gnss Measurements ◽  
Natural Laboratory

<p>Dynamics of polar outlet glaciers vary with ocean tides, providing a natural laboratory to understand basal processes beneath ice streams, ice rheology and ice-shelf buttressing. We apply Terrestrial Radar Interferometry to close the spatiotemporal gap between localized, temporally well-resolved GNSS and area-wide but sparse satellite observations. Three-hour flowfields collected over an eight day period at Priestley Glacier, Antarctica, validate and provide the spatial context for concurrent GNSS measurements. Ice flow is fastest during falling tides and slowest during rising tides. Principal components of the timeseries prove upstream propagation of tidal signatures $>$ 10 km away from the grounding line. Hourly, cm-scale horizontal and vertical flexure patterns occur $>$6 km upstream of the grounding line. Vertical uplift upstream of the grounding line is consistent with ephemeral re-grounding during low-tide impacting grounding-zone stability. On the freely floating ice shelves, we find velocity peaks both during high- and low-tide suggesting that ice-shelf buttressing varies temporally as a function of flexural bending from tidal displacement. Taken together, these observations identify tidal imprints on ice-stream dynamics on new temporal and spatial scales providing constraints for models designed to isolate dominating processes in ice-stream and ice-shelf mechanics.</p>

scholarly journals Modeling the elastic transmission of tidal stresses to great distances inland in channelized ice streams

2014 ◽  
Vol 8 (6) ◽  
pp. 2007-2029 ◽  
Author(s):  
J. Thompson ◽  
M. Simons ◽  
V. C. Tsai
Keyword(s):  
Three Dimensional ◽  
Hydrologic Model ◽  
Ice Streams ◽  
Ice Stream ◽  
Nonlinear Viscoelastic ◽  
Grounding Line ◽  
Dimensional Finite Element ◽  
Order Of Magnitude ◽  
Three Dimensional Finite Element ◽  
The Impact

Abstract. Geodetic surveys suggest that ocean tides can modulate the motion of Antarctic ice streams, even at stations many tens of kilometers inland from the grounding line. These surveys suggest that ocean tidal stresses can perturb ice stream motion at distances about an order of magnitude farther inland than tidal flexure of the ice stream alone. Recent models exploring the role of tidal perturbations in basal shear stress are primarily one- or two-dimensional, with the impact of the ice stream margins either ignored or parameterized. Here, we use two- and three-dimensional finite-element modeling to investigate transmission of tidal stresses in ice streams and the impact of considering more realistic, three-dimensional ice stream geometries. Using Rutford Ice Stream as a real-world comparison, we demonstrate that the assumption that elastic tidal stresses in ice streams propagate large distances inland fails for channelized glaciers due to an intrinsic, exponential decay in the stress caused by resistance at the ice stream margins. This behavior is independent of basal conditions beneath the ice stream and cannot be fit to observations using either elastic or nonlinear viscoelastic rheologies without nearly complete decoupling of the ice stream from its lateral margins. Our results suggest that a mechanism external to the ice stream is necessary to explain the tidal modulation of stresses far upstream of the grounding line for narrow ice streams. We propose a hydrologic model based on time-dependent variability in till strength to explain transmission of tidal stresses inland of the grounding line. This conceptual model can reproduce observations from Rutford Ice Stream.

scholarly journals Modeling the elastic transmission of tidal stresses to great distances inland in channelized ice streams

2014 ◽  
Vol 8 (2) ◽  
pp. 2119-2177 ◽  
Author(s):  
J. Thompson ◽  
M. Simons ◽  
V. C. Tsai
Keyword(s):  
Three Dimensional ◽  
Hydrologic Model ◽  
Ocean Tides ◽  
Ice Streams ◽  
Ice Stream ◽  
Nonlinear Viscoelastic ◽  
Grounding Line ◽  
Order Of Magnitude ◽  
Three Dimensional Finite Element ◽  
The Impact

Abstract. Geodetic surveys suggest that ocean tides can modulate the motion of Antarctic ice streams. Data from Whillans Ice Plain, Rutford Ice Stream, and other Antarctic ice streams show periodicity in flow velocity at periods similar to those of ocean tides at geodetic stations many tens of kilometers inland from the grounding line. These data suggest that ocean tidal stresses can perturb ice stream motion at distances about an order of magnitude farther inland than tidal flexure of the ice stream alone. Recent models exploring the role of tidal perturbations in basal shear stress are primarily two-dimensional, with the impact of the ice stream margins either ignored or parameterized. Here, we use two- and three-dimensional finite element modeling to investigate transmission of tidal stresses in ice streams and the impact of considering more realistic, three-dimensional ice stream geometries. Using Rutford Ice Stream as a real-world comparison, we demonstrate that the assumption that elastic tidal stresses in ice streams propagate large distances inland fails for channelized glaciers due to an intrinsic, exponential decay in the stress due to resistance at the ice stream margins. This behavior is independent of basal conditions beneath the ice stream and cannot be fit to observations using either elastic or nonlinear viscoelastic rheologies without nearly complete decoupling of the ice stream from its lateral margins. Our results suggest that a mechanism external to the ice stream is necessary to explain the tidal modulation of stresses far upstream of the grounding line for narrow ice streams. We propose a hydrologic model based on time-dependent variability in till strength to explain transmission of tidal stresses inland of the grounding line. This conceptual model reproduces observations from Rutford Ice Stream.

scholarly journals Deglaciation and future stability of the Coats Land ice margin, Antarctica

2018 ◽  
Author(s):  
Dominic A. Hodgson ◽  
Kelly Hogan ◽  
James Smith ◽  
James A. Smith ◽  
Claus-Dieter Hillenbrand ◽  
...  
Keyword(s):  
Seismic Reflection ◽  
Structural Integrity ◽  
Ice Sheet ◽  
Weddell Sea ◽  
Ice Streams ◽  
Ice Shelves ◽  
Ice Stream ◽  
Grounding Line ◽  
Loss Of Contact ◽  
Seismic Reflection Profiles

Abstract. The East Antarctic Ice Sheet discharges into the Weddell Sea via the Coats Land ice margin. We have used geophysical data to determine the changing ice sheet configuration in this region through its last advance and retreat, and identify constraints on its future stability. Methods included high-resolution multibeam-bathymetry, sub-bottom profiles, seismic-reflection profiles, sediment core analysis and satellite altimetry. These provide evidence that Coats Land glaciers and ice streams merged with the palaeo-Filchner Ice Stream during the last ice advance. Retreat of this ice stream from 12.8 to 8.4 cal kyr BP resulted in its progressive southwards decoupling from Coats Land glaciers. Moraines and grounding-zone wedges document the subsequent retreat and thinning of these glaciers, loss of contact with the bed, and the formation of ice shelves, which re-advanced to pinning points on topographic highs at the distal end of their troughs. Once detached from the bed, the ice shelves were predisposed to rapid retreat back to coastal grounding lines due to reverse-bed slopes, the absence of further pinning points, and potentially to the loss of structural integrity propagating from the grounding line. These processes explain why there are no large ice shelves from 75.5-77° S.

scholarly journals Persistence and variability of ice-stream grounding lines on retrograde bed slopes

2016 ◽  
Vol 10 (4) ◽  
pp. 1883-1896 ◽  
Author(s):  
Alexander A. Robel ◽  
Christian Schoof ◽  
Eli Tziperman
Keyword(s):  
Stream Flow ◽  
Flow Line ◽  
Reverse Direction ◽  
West Antarctica ◽  
Ice Streams ◽  
Basal Resistance ◽  
Physical Mechanisms ◽  
Ice Stream ◽  
Grounding Line ◽  
Transient Variations

Abstract. In many ice streams, basal resistance varies in space and time due to the dynamically evolving properties of subglacial till. These variations can cause internally generated oscillations in ice-stream flow. However, the potential for such variations in basal properties is not considered by conventional theories of grounding-line stability on retrograde bed slopes, which assume that bed properties are static in time. Using a flow-line model, we show how internally generated, transient variations in ice-stream state interact with retrograde bed slopes. In contrast to predictions from the theory of the marine ice-sheet instability, our simulated grounding line is able to persist and reverse direction of migration on a retrograde bed when undergoing oscillations in the grounding-line position. In turn, the presence of a retrograde bed may also suppress or reduce the amplitude of internal oscillations in ice-stream state. We explore the physical mechanisms responsible for these behaviors and discuss the implications for observed grounding-line migration in West Antarctica.

scholarly journals On the Disintegration of Ice Shelves: the Role of Thinning

1982 ◽  
Vol 3 ◽  
pp. 146-151 ◽  
Author(s):  
T. J. Hughes
Keyword(s):  
Weak Links ◽  
Ice Melting ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Shelves ◽  
Ross Ice Shelf ◽  
Tidal Pumping ◽  
Grounding Line ◽  
Converging Flow

It is proposed that an ice shelf disintegrates when its calving front retreats faster than its grounding line. This paper examines the role of ice thinning in grounding-line retreat. Thinning occurs as a result of creep spreading and ice melting. Thinning by creep is examined for the general regime of bending converging flow in an ice shelf lying in a confined embayment, and at the grounding lines of ice streams that supply the ice shelf and ice rises where the ice shelf is grounded on bedrock. Thinning by melting is examined at these grounding lines for tidal pumping and for descent of surface melt water into strandline crevasses, where concentrated melting is focused at the supposed weak links that connect the ice shelf to its embayment, its ice streams, and its ice rises. Applications are made to the Ross Ice Shelf.

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