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

The Cryosphere ◽

10.5194/tc-12-2383-2018 ◽

2018 ◽

Vol 12 (7) ◽

pp. 2383-2399 ◽

Cited By ~ 6

Author(s):

Dominic A. Hodgson ◽

Kelly Hogan ◽

James M. Smith ◽

James A. Smith ◽

Claus-Dieter Hillenbrand ◽

...

Keyword(s):

Structural Integrity ◽

Ice Sheet ◽

Weddell Sea ◽

Ice Streams ◽

Ice Shelves ◽

Last Glacial ◽

Ice Stream ◽

Loss Of Contact ◽

Seismic Reflection Profiles ◽

Glacial Advance

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 glacial advance and Holocene retreat and to 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 glacial advance. Retreat of this ice stream from 12 848 to 8351 cal. yr BP resulted in its progressive southwards decoupling from Coats Land outlet glaciers. Moraines and grounding-zone wedges document the subsequent retreat and thinning of these glaciers, their 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 the troughs. Once fully detached from the bed, these ice shelves were predisposed to rapid retreat back to coastal grounding lines. This was due to reverse-bed slopes, the consequent absence of further pinning points in the troughs and potentially to the loss of structural integrity resulting from weaknesses inherited at the grounding line. These processes explain why there are no large ice shelves in the eastern Weddell Sea between 75.5 and 77∘ S.

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Past and future dynamics of the Brunt Ice Shelf from seabed bathymetry and ice shelf geometry

10.5194/tc-2018-206 ◽

2018 ◽

Author(s):

Dominic A. Hodgson ◽

Tom A. Jordan ◽

Jan De Rydt ◽

Peter T. Fretwell ◽

Samuel A. Seddon ◽

...

Keyword(s):

Structural Integrity ◽

Ice Shelf ◽

Partial Loss ◽

Ice Streams ◽

Ice Shelves ◽

Subsequent Response ◽

Grounding Line ◽

Loss Of Contact ◽

Seabed Bathymetry ◽

Accelerated Flow

Abstract. The recent rapid growth of rifts in the Brunt Ice Shelf appears to signal the onset of its largest calving event since records began in 1915. The aim of this study is to determine whether this calving event will lead to a new steady state where the Brunt Ice Shelf remains in contact with the bed, or an unpinning from the bed, which could pre-dispose it to accelerated flow or possible break-up. We use a range of geophysical data to reconstruct the seafloor bathymetry and ice shelf geometry, to examine past ice sheet configurations in the Brunt Basin, and to define the present-day geometry of the contact between the Brunt Ice Shelf and the bed. Results show that during past ice advances grounded ice streams converged in the Brunt Basin from the south and east. The ice then retreated pausing on at least three former grounding lines marked by topographic highs, and transverse ridges on the flanks of the basin. These have subsequently formed pinning points for advancing ice shelves. The ice shelf geometry and bathymetry measurements show that the base of the Brunt Ice Shelf now only makes contact with one of these topographic highs. This contact is limited to an area of less than 1.3 to 3 km2 and results in a compressive regime that helps to maintain the ice shelf. The maximum overlap between ice shelf thickness and the bathymetry is 2–25 m, and is contingent on the presence of incorporated iceberg keels, which protrude beneath the base of the ice shelf. The future of the ice shelf is dependent on whether the expected calving event causes full or partial loss of contact with the bed, and whether the subsequent response causes re-grounding within a predictable period, or a loss of structural integrity resulting from properties inherited at the grounding line.

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Past and future dynamics of the Brunt Ice Shelf from seabed bathymetry and ice shelf geometry

The Cryosphere ◽

10.5194/tc-13-545-2019 ◽

2019 ◽

Vol 13 (2) ◽

pp. 545-556 ◽

Cited By ~ 8

Author(s):

Dominic A. Hodgson ◽

Tom A. Jordan ◽

Jan De Rydt ◽

Peter T. Fretwell ◽

Samuel A. Seddon ◽

...

Keyword(s):

Structural Integrity ◽

Ice Shelf ◽

Ice Streams ◽

Ice Shelves ◽

Sea Floor ◽

Subsequent Response ◽

Grounding Line ◽

Loss Of Contact ◽

Seabed Bathymetry ◽

Accelerated Flow

Abstract. The recent rapid growth of rifts in the Brunt Ice Shelf appears to signal the onset of its largest calving event since records began in 1915. The aim of this study is to determine whether this calving event will lead to a new steady state in which the Brunt Ice Shelf remains in contact with the bed, or an unpinning from the bed, which could predispose it to accelerated flow or possible break-up. We use a range of geophysical data to reconstruct the sea-floor bathymetry and ice shelf geometry, to examine past ice sheet configurations in the Brunt Basin, and to define the present-day geometry of the contact between the Brunt Ice Shelf and the bed. Results show that during past ice advances grounded ice streams likely converged in the Brunt Basin from the south and east. As the ice retreated, it was likely pinned on at least three former grounding lines marked by topographic highs, and transverse ridges on the flanks of the basin. These may have subsequently formed pinning points for developing ice shelves. The ice shelf geometry and bathymetry measurements show that the base of the Brunt Ice Shelf now only makes contact with one of these topographic highs. This contact is limited to an area of less than 1.3 to 3 km2 and results in a compressive regime that helps to maintain the ice shelf's integrity. The maximum overlap between ice shelf draft and the bathymetric high is 2–25 m and is contingent on the presence of incorporated iceberg keels, which protrude beneath the base of the ice shelf. The future of the ice shelf depends on whether the expected calving event causes full or partial loss of contact with the bed and whether the subsequent response causes re-grounding within a predictable period or a loss of structural integrity resulting from properties inherited at the grounding line.

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Basal topographic controls on the stability of the West Antarctic ice sheet: lessons from Foundation Ice Stream

Annals of Glaciology ◽

10.1017/aog.2017.9 ◽

2017 ◽

Vol 58 (75pt2) ◽

pp. 193-198 ◽

Cited By ~ 1

Author(s):

Kathleen Huybers ◽

Gerard Roe ◽

Howard Conway

Keyword(s):

Sea Level ◽

Ice Sheet ◽

Weddell Sea ◽

Significant Advance ◽

Ice Streams ◽

Antarctic Ice Sheet ◽

West Antarctic Ice Sheet ◽

West Antarctic ◽

Ice Stream ◽

Grounding Line

ABSTRACT Using observations of basal topography, ice thickness and modern accumulation rates, we use theory and a dynamic flowline model to examine the sensitivity of Antarctica's Foundation Ice Stream to changes in sea level, accumulation and buttressing at the grounding line. Our sensitivity studies demonstrate that the steep, upward-sloping basal topography inland from the grounding line serves to stabilize retreat of the ice stream, while the upward-sloping submarine topography downstream from the grounding line creates the potential for significant advance under conditions of modest sea-level lowering and/or increased accumulation rate. Extrapolating from Foundation Ice Stream, many nearby Weddell Sea sector ice streams are in a similar configuration, suggesting that the historical and projected responses of this sector's ice streams may contrast with those in the Amundsen or Ross Sea sectors. This work reaffirms that the greatest concerns for rapid West Antarctic Ice Sheet (WAIS) retreat are locations of reverse slopes, muted basal topography and limited lateral support.

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Drivers of abrupt Holocene shifts in West Antarctic ice stream direction determined from combined ice sheet modelling and geologic signatures

Antarctic Science ◽

10.1017/s0954102014000613 ◽

2014 ◽

Vol 26 (6) ◽

pp. 674-686 ◽

Cited By ~ 16

Author(s):

C.J. Fogwill ◽

C.S.M. Turney ◽

N.R. Golledge ◽

D.H. Rood ◽

K. Hippe ◽

...

Keyword(s):

Flow Direction ◽

Ice Sheet ◽

Weddell Sea ◽

Last Deglaciation ◽

Ice Streams ◽

Antarctic Ice Sheet ◽

West Antarctic Ice Sheet ◽

West Antarctic ◽

Ice Stream ◽

Ice Sheet Modelling

AbstractDetermining the millennial-scale behaviour of marine-based sectors of the West Antarctic Ice Sheet (WAIS) is critical to improve predictions of the future contribution of Antarctica to sea level rise. Here high-resolution ice sheet modelling was combined with new terrestrial geological constraints (in situ14C and 10Be analysis) to reconstruct the evolution of two major ice streams entering the Weddell Sea over 20 000 years. The results demonstrate how marked differences in ice flux at the marine margin of the expanded Antarctic ice sheet led to a major reorganization of ice streams in the Weddell Sea during the last deglaciation, resulting in the eastward migration of the Institute Ice Stream, triggering a significant regional change in ice sheet mass balance during the early to mid Holocene. The findings highlight how spatial variability in ice flow can cause marked changes in the pattern, flux and flow direction of ice streams on millennial timescales in this marine ice sheet setting. Given that this sector of the WAIS is assumed to be sensitive to ocean-forced instability and may be influenced by predicted twenty-first century ocean warming, our ability to model and predict abrupt and extensive ice stream diversions is key to a realistic assessment of future ice sheet sensitivity.

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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

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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The Dynamics of Marine Ice Sheets

Journal of Glaciology ◽

10.3189/s0022143000014726 ◽

1979 ◽

Vol 24 (90) ◽

pp. 167-177 ◽

Cited By ~ 13

Author(s):

Robert H. Thomas

Keyword(s):

Sea Level ◽

Ice Sheets ◽

Ice Sheet ◽

Ice Shelf ◽

Ice Streams ◽

Ice Shelves ◽

The North ◽

West Antarctic ◽

Grounding Line ◽

Ice Sheet Dynamics

AbstractMarine ice sheets rest on land that, for the most part, is below sea-level. Ice that flows across the grounding line, where the ice sheet becomes afloat, either calves into icebergs or forms a floating ice shelf joined to the ice sheet. At the grounding line there is a transition from ice-sheet dynamics to ice-shelf dynamics, and the creep-thinning rate in this region is very sensitive to sea depth; rising sea-level causes increased thinning-rates and grounding-line retreat, falling sea-level has the reverse effect. If the bedrock slopes down towards the centre of the ice sheet there may be only two stable modes: a freely-floating ice shelf or a marine ice sheet that extends to the edge of the continental shelf. Once started, collapse of such an ice sheet to form an ice shelf may take place extremely rapidly. Ice shelves which form in embayments of a marine ice sheet, or which are partially grounded, have a stabilizing influence since ice flowing across the grounding line has to push the ice shelf past its sides. Retreat of the grounding line tends to enlarge the ice shelf, which ultimately may become large enough to prevent excessive outflow from the ice sheet so that a new equilibrium grounding line is established; removal of the ice shelf would allow retreat to continue. During the late-Wisconsin glacial maximum there may have been marine ice sheets in the northern hemisphere but the only current example is the West Antarctic ice sheet. This is buttressed by the Ross and Ronne Ice Shelves, and if climatic warming were to prohibit the existence of these ice shelves then the ice sheet would collapse. Field observations suggest that, at present, the ice sheet may be advancing into parts of the Ross Ice Shelf. Such advance, however, would not ensure the security of the ice sheet since ice streams that drain to the north appear to flow directly into the sea with little or no ice shelf to buttress them. If these ice streams do not flow over a sufficiently high bedrock sill then they provide the most likely avenues for ice-sheet retreat.

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

10.5194/egusphere-egu21-15197 ◽

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

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.

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Identifying Antarctic Ice Sheet Tipping Points

10.5194/egusphere-egu2020-7874 ◽

2020 ◽

Author(s):

Bradley Reed ◽

Mattias Green ◽

Hilmar Gudmundsson ◽

Adrian Jenkins

Keyword(s):

Ice Sheet ◽

Fold Increase ◽

Tipping Points ◽

Ice Streams ◽

Antarctic Ice Sheet ◽

Ice Shelves ◽

Ice Stream ◽

The Stability ◽

Basal Melting ◽

Gradual Variation

Warmer atmospheric and oceanic temperatures have led to a six-fold increase in mass loss from Antarctica in the last four decades. It is difficult to predict how the ice sheet will respond to future warming because it is subject to positive feedback mechanisms, which could lead to destabilisation. Observational and modelling work has shown that ice streams in West Antarctica may be undergoing unstable and possibly irreversible retreat due to increased basal melting beneath their ice shelves. Being able to identify and predict stability thresholds in ice streams draining the Antarctic Ice Sheet could help establish early warning indicators of near-future abrupt changes in sea level.&#160; &#160; Here, we use the shallow-ice flow model &#218;a to investigate the stability of an idealised ice stream from the third Marine Ice Sheet Model Intercomparison Project (MISMIP+). Initial results show that a gradual variation in ice viscosity, which corresponds to a change in temperature, causes the ice stream to undergo hysteresis across an overdeepened bed. This hysteresis means there are two tipping points, one for an advance phase and one for a retreat phase, both of which lie off the retrograde sloping bedrock. Beyond these tipping points, changes in ice stream grounding line position are unstable and irreversible. This behaviour is also apparent in wider ice streams although there is a change to the onset of instability and the location of tipping points. Further studies will investigate the additional effects of basal melting on these tipping points.

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