scholarly journals Dynamic influence of pinning points on marine ice-sheet stability: a numerical study in Dronning Maud Land, East Antarctica

2016 ◽  
Author(s):  
Lionel Favier ◽  
Frank Pattyn ◽  
Sophie Berger ◽  
Reinhard Drews
Keyword(s):  
Data Assimilation ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
East Antarctica ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Ice Shelves ◽  
Grounding Line ◽  
Dronning Maud Land

Abstract. The East Antarctic ice sheet is likely more stable than its West Antarctic counterpart, because its bed is largely lying above sea level. However, the ice sheet in Dronning Maud Land, East Antarctica, contains marine sectors that are in contact with the ocean through overdeepened marine basins interspersed by (more stable) grounded ice promontories and ice rises, pinning and stabilising the ice shelves. In this paper, we use the ice-sheet model BISICLES to investigate the effect of sub-ice shelf melting, using a series of scenarios compliant with current values, on the ice-dynamic stability of the outlet glaciers between the Lazarev and Roi Baudouin ice shelves over the next millennia. Overall, the sub-ice shelf melting substantially impacts the sea level contribution. Locally, we predict a short-term rapid grounding-line retreat of the overdeepened outlet glacier Hansenbreen, which further induces the collapse of the bordering ice promontories into ice rises. Furthermore, our analysis demonstrates that the onset of the marine ice-sheet retreat and subsequent promontory collapse is controlled by small pinning points within the ice shelves, mostly uncharted in pan-Antarctic datasets. Pinning points have a twofold impact on marine ice sheets. They decrease the ice discharge by buttressing effect, and play a crucial role in initialising marine ice sheets through data assimilation, leading to errors in ice-shelf rheology when omitted. Our results show that unpinning has a small effect on the total amount of sea level rise but locally affects the timing of grounding-line migration, advancing the collapse of a promontory by hundreds of years. On the other hand, omitting the same pinning point in data assimilation decreases the sea level contribution by 10 % and delays the promontory collapse by almost a millennium. This very subtle influence of pinning points on ice dynamics acts on kilometre scale and calls for a better knowledge of the Antarctic margins that will improve sea-level predictions.

scholarly journals Dynamic influence of pinning points on marine ice-sheet stability: a numerical study in Dronning Maud Land, East Antarctica

2016 ◽  
Vol 10 (6) ◽  
pp. 2623-2635 ◽  
Author(s):  
Lionel Favier ◽  
Frank Pattyn ◽  
Sophie Berger ◽  
Reinhard Drews
Keyword(s):  
Data Assimilation ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
East Antarctica ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Outlet Glacier ◽  
Ice Shelves ◽  
Dronning Maud Land

Abstract. The East Antarctic ice sheet is likely more stable than its West Antarctic counterpart because its bed is largely lying above sea level. However, the ice sheet in Dronning Maud Land, East Antarctica, contains marine sectors that are in contact with the ocean through overdeepened marine basins interspersed by grounded ice promontories and ice rises, pinning and stabilising the ice shelves. In this paper, we use the ice-sheet model BISICLES to investigate the effect of sub-ice-shelf melting, using a series of scenarios compliant with current values, on the ice-dynamic stability of the outlet glaciers between the Lazarev and Roi Baudouin ice shelves over the next millennium. Overall, the sub-ice-shelf melting substantially impacts the sea-level contribution. Locally, we predict a short-term rapid grounding-line retreat of the overdeepened outlet glacier Hansenbreen, which further induces the transition of the bordering ice promontories into ice rises. Furthermore, our analysis demonstrated that the onset of the marine ice-sheet retreat and subsequent promontory transition into ice rise is controlled by small pinning points, mostly uncharted in pan-Antarctic datasets. Pinning points have a twofold impact on marine ice sheets. They decrease the ice discharge by buttressing effect, and they play a crucial role in initialising marine ice sheets through data assimilation, leading to errors in ice-shelf rheology when omitted. Our results show that unpinning increases the sea-level rise by 10 %, while omitting the same pinning point in data assimilation decreases it by 10 %, but the more striking effect is in the promontory transition time, advanced by two centuries for unpinning and delayed by almost half a millennium when the pinning point is missing in data assimilation. Pinning points exert a subtle influence on ice dynamics at the kilometre scale, which calls for a better knowledge of the Antarctic margins.

scholarly journals Changes in ice dynamics and mass balance of the Antarctic ice sheet

2006 ◽  
Vol 364 (1844) ◽  
pp. 1637-1655 ◽  
Author(s):  
Eric Rignot
Keyword(s):  
Mass Balance ◽  
Sea Level ◽  
Ice Sheet ◽  
East Antarctica ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
The Antarctic

The concept that the Antarctic ice sheet changes with eternal slowness has been challenged by recent observations from satellites. Pronounced regional warming in the Antarctic Peninsula triggered ice shelf collapse, which led to a 10-fold increase in glacier flow and rapid ice sheet retreat. This chain of events illustrated the vulnerability of ice shelves to climate warming and their buffering role on the mass balance of Antarctica. In West Antarctica, the Pine Island Bay sector is draining far more ice into the ocean than is stored upstream from snow accumulation. This sector could raise sea level by 1 m and trigger widespread retreat of ice in West Antarctica. Pine Island Glacier accelerated 38% since 1975, and most of the speed up took place over the last decade. Its neighbour Thwaites Glacier is widening up and may double its width when its weakened eastern ice shelf breaks up. Widespread acceleration in this sector may be caused by glacier ungrounding from ice shelf melting by an ocean that has recently warmed by 0.3 °C. In contrast, glaciers buffered from oceanic change by large ice shelves have only small contributions to sea level. In East Antarctica, many glaciers are close to a state of mass balance, but sectors grounded well below sea level, such as Cook Ice Shelf, Ninnis/Mertz, Frost and Totten glaciers, are thinning and losing mass. Hence, East Antarctica is not immune to changes.

scholarly journals The Dynamics of Marine Ice Sheets

1979 ◽  
Vol 24 (90) ◽  
pp. 167-177 ◽  
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.

scholarly journals The Dynamics of Marine Ice Sheets

1979 ◽  
Vol 24 (90) ◽  
pp. 167-177 ◽  
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.

scholarly journals Sea-level response to melting of Antarctic ice shelves on multi-centennial timescales with the fast Elementary Thermomechanical Ice Sheet model (f.ETISh v1.0)

2017 ◽  
Vol 11 (4) ◽  
pp. 1851-1878 ◽  
Author(s):  
Frank Pattyn
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Power Law ◽  
Coulomb Friction ◽  
Ice Sheet ◽  
East Antarctica ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Grounding Line ◽  
Basal Sliding

Abstract. The magnitude of the Antarctic ice sheet's contribution to global sea-level rise is dominated by the potential of its marine sectors to become unstable and collapse as a response to ocean (and atmospheric) forcing. This paper presents Antarctic sea-level response to sudden atmospheric and oceanic forcings on multi-centennial timescales with the newly developed fast Elementary Thermomechanical Ice Sheet (f.ETISh) model. The f.ETISh model is a vertically integrated hybrid ice sheet–ice shelf model with vertically integrated thermomechanical coupling, making the model two-dimensional. Its marine boundary is represented by two different flux conditions, coherent with power-law basal sliding and Coulomb basal friction. The model has been compared to existing benchmarks. Modelled Antarctic ice sheet response to forcing is dominated by sub-ice shelf melt and the sensitivity is highly dependent on basal conditions at the grounding line. Coulomb friction in the grounding-line transition zone leads to significantly higher mass loss in both West and East Antarctica on centennial timescales, leading to 1.5 m sea-level rise after 500 years for a limited melt scenario of 10 m a−1 under freely floating ice shelves, up to 6 m for a 50 m a−1 scenario. The higher sensitivity is attributed to higher ice fluxes at the grounding line due to vanishing effective pressure. Removing the ice shelves altogether results in a disintegration of the West Antarctic ice sheet and (partially) marine basins in East Antarctica. After 500 years, this leads to a 5 m and a 16 m sea-level rise for the power-law basal sliding and Coulomb friction conditions at the grounding line, respectively. The latter value agrees with simulations by DeConto and Pollard (2016) over a similar period (but with different forcing and including processes of hydrofracturing and cliff failure). The chosen parametrizations make model results largely independent of spatial resolution so that f.ETISh can potentially be integrated in large-scale Earth system models.

scholarly journals Marine Ice Sheet Instability and Ice Shelf Buttressing Influenced Deglaciation of the Minch Ice Stream, Northwest Scotland

2018 ◽  
Author(s):  
Niall Gandy ◽  
Lauren J. Gregoire ◽  
Jeremy C. Ely ◽  
Christopher D. Clark ◽  
David M. Hodgson ◽  
...  
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Last Deglaciation ◽  
Ice Shelf ◽  
Dynamical Processes ◽  
Ice Dynamics ◽  
Surface Mass ◽  
Ice Shelves ◽  
Ice Stream ◽  
The Last Deglaciation

Abstract. Uncertainties in future sea level projections are dominated by our limited understanding of the dynamical processes that control instabilities of marine ice sheets. A valuable case to examine these processes is the last deglaciation of the British-Irish Ice Sheet. The Minch Ice Stream, which drained a large proportion of ice from the northwest sector of the British-Irish Ice Sheet during the last deglaciation, is well constrained, with abundant empirical data which could be used to inform, validate and analyse numerical ice sheet simulations. We use BISICLES, a higher-order ice sheet model, to examine the dynamical processes that controlled the retreat of the Minch Ice Stream. We simulate retreat from the shelf edge under constant "warm" surface mass balance and subshelf melt, to isolate the role of internal ice dynamics from external forcings. The model simulates a slowdown of retreat as the ice stream becomes laterally confined at a "pinning-point" between mainland Scotland and the Isle of Lewis. At this stage, the presence of ice shelves became a major control on deglaciation, providing buttressing to upstream ice. Subsequently, the presence of a reverse slope inside the Minch Strait produces an acceleration in retreat, leading to a "collapsed" state, even when the climate returns to the initial "cold" conditions. Our simulations demonstrate the importance of the Marine Ice Sheet Instability and ice shelf buttressing during the deglaciation of parts of the British-Irish Ice Sheet. Thus, geological data could be used to constrain these processes in ice sheet models used for projecting the future of our contemporary ice sheets.

scholarly journals Numerical modelling of ice-sheet dynamics across the Vostok subglacial lake, central East Antarctica

2000 ◽  
Vol 46 (153) ◽  
pp. 197-205 ◽  
Author(s):  
Christoph Mayer ◽  
Martin J. Siegert
Keyword(s):  
Lake Water ◽  
Ice Sheet ◽  
East Antarctica ◽  
Particle Flow ◽  
Ice Shelf ◽  
Flow Paths ◽  
Ice Dynamics ◽  
Subglacial Lake ◽  
Grounding Line ◽  
Ice Sheet Dynamics

AbstractA numerical model of the ice-sheet/ice-shelf transition was used to investigate ice-sheet dynamics across the large subglacial lake beneath Vostok station, central East Antarctica. European Remote-sensing Satellite (ERS-1) altimetry of the ice surface and 60 MHz radio-echo sounding (RES) of the ice-sheet base and internal ice-sheet layering were used to develop a conceptual flowline across the ice sheet, which the model used as input. The model calculates horizontal and vertical velocities and stresses, from which particle flow paths can be obtained, and the ice-sheet temperature distribution. An inverse approach to modelling was adopted, where particle flow paths were forced to match those identified from internal RES layering. Results show that ice dynamics across the inflow grounding line are similar to an ice-sheet/ice-shelf transition. Model particle flow paths match internal RES layering when ice is (a) taken away from the ice base across the first 2 km of the flowline over the lake and (b) added to the base across the remainder of the lake. We contend that the process causing this transfer of ice is likely to be melting of ice and freezing of water at the ice–water interface. Other explanations, such as enhanced rates of accumulation over the grounding line, or three-dimensional convergent/divergent flow of ice are inconsistent with available measurements. Such melting and refreezing would be responsible for circulation and mixing of at least the surface layers of the lake water. Our model suggests that several tens of metres of refrozen “basal ice” would accrete from lake water to the ice sheet before the ice regrounds.

scholarly journals Sea-level response to melting of Antarctic ice shelves on multi-centennial time scales with the fast Elementary Thermomechanical Ice Sheet model (f.ETISh v1.0)

2017 ◽  
Author(s):  
Frank Pattyn
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Time Scales ◽  
Power Law ◽  
Coulomb Friction ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Grounding Line ◽  
Basal Sliding

Abstract. The magnitude of the Antarctic ice sheet's contribution to global sea-level rise is dominated by the potential of its marine sectors to become unstable and collapse as a response to ocean (and atmospheric) forcing. This paper presents Antarctic sea-level response to sudden atmospheric and oceanic forcings on multi-centennial time scales with the newly developed fast Elementary Thermomechanical Ice Sheet (f.ETISh) model. The f.ETISh model is a vertically integrated hybrid ice sheet/ice shelf model with an approximate implementation of ice sheet thermomechanics, making the model two-dimensional. Its marine boundary is represented by two different flux conditions, coherent with power-law basal sliding and Coulomb basal friction. The model has been compared to a series of existing benchmarks. Modelled Antarctic ice sheet response to forcing is dominated by sub-ice shelf melt and the sensitivity is highly dependent on basal conditions at the grounding line. Coulomb friction in the grounding-line transition zone leads to significantly higher mass loss in both West and East Antarctica on centennial time scales, leading to 2 m sea level rise after 500 years for a moderate melt scenario of 20 m a−1 under freely-floating ice shelves, up to 6 m for a 50 m a−1 scenario. The higher sensitivity is attributed to higher driving stresses upstream from the grounding line. Removing the ice shelves altogether results in a disintegration of the West Antarctic ice sheet and (partially) marine basins in East Antarctica. After 500 years, this leads to a 4.5 m and a 12.2 m sea level rise for the power-law basal sliding and Coulomb friction conditions at the grounding line, respectively. The latter value agrees with simulations by DeConto and Pollard (2016) over a similar period (but with different forcing and including processes of hydro-fracturing and cliff failure). The chosen parametrizations make model results largely independent of spatial resolution, so that f.ETISh can potentially be integrated in large-scale Earth system models.

scholarly journals Simulation of the Greenland Ice Sheet over two glacial–interglacial cycles: investigating a sub-ice- shelf melt parameterization and relative sea level forcing in an ice-sheet–ice-shelf model

2018 ◽  
Vol 14 (5) ◽  
pp. 619-635 ◽  
Author(s):  
Sarah L. Bradley ◽  
Thomas J. Reerink ◽  
Roderik S. W. van de Wal ◽  
Michiel M. Helsen
Keyword(s):  
Continental Shelf ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Shelf ◽  
Temporal Behaviour ◽  
Ice Shelves ◽  
Non Local ◽  
Continental Shelf Break

Abstract. Observational evidence, including offshore moraines and sediment cores, confirm that at the Last Glacial Maximum (LGM) the Greenland ice sheet (GrIS) expanded to a significantly larger spatial extent than seen at present, grounding into Baffin Bay and out onto the continental shelf break. Given this larger spatial extent and its close proximity to the neighbouring Laurentide Ice Sheet (LIS) and Innuitian Ice Sheet (IIS), it is likely these ice sheets will have had a strong non-local influence on the spatial and temporal behaviour of the GrIS. Most previous paleo ice-sheet modelling simulations recreated an ice sheet that either did not extend out onto the continental shelf or utilized a simplified marine ice parameterization which did not fully include the effect of ice shelves or neglected the sensitivity of the GrIS to this non-local bedrock signal from the surrounding ice sheets. In this paper, we investigated the evolution of the GrIS over the two most recent glacial–interglacial cycles (240 ka BP to the present day) using the ice-sheet–ice-shelf model IMAU-ICE. We investigated the solid earth influence of the LIS and IIS via an offline relative sea level (RSL) forcing generated by a glacial isostatic adjustment (GIA) model. The RSL forcing governed the spatial and temporal pattern of sub-ice-shelf melting via changes in the water depth below the ice shelves. In the ensemble of simulations, at the glacial maximums, the GrIS coalesced with the IIS to the north and expanded to the continental shelf break to the southwest but remained too restricted to the northeast. In terms of the global mean sea level contribution, at the Last Interglacial (LIG) and LGM the ice sheet added 1.46 and −2.59 m, respectively. This LGM contribution by the GrIS is considerably higher (∼ 1.26 m) than most previous studies whereas the contribution to the LIG highstand is lower (∼ 0.7 m). The spatial and temporal behaviour of the northern margin was highly variable in all simulations, controlled by the sub-ice-shelf melting which was dictated by the RSL forcing and the glacial history of the IIS and LIS. In contrast, the southwestern part of the ice sheet was insensitive to these forcings, with a uniform response in all simulations controlled by the surface air temperature, derived from ice cores.

scholarly journals A three-dimensional full Stokes model of the grounding line dynamics: effect of a pinning point beneath the ice shelf

2011 ◽  
Vol 5 (4) ◽  
pp. 1995-2033 ◽  
Author(s):  
L. Favier ◽  
O. Gagliardini ◽  
G. Durand ◽  
T. Zwinger
Keyword(s):  
Sea Level ◽  
Contact Point ◽  
Ice Sheet ◽  
Mathematical Representation ◽  
Major Influence ◽  
Large Area ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Flow Equations ◽  
Grounding Line

Abstract. The West Antarctic ice sheet is confined by a large area of ice shelves, fed by inland ice through fast flowing ice streams. The dynamics of the grounding line, i.e. the line-boundary between grounded ice and the downstream ice shelf, has a major influence on the dynamics of the whole ice sheet. However, most of the ice sheet models use simplifications of the flow equations, i.e., they do not include all the stress components, and are known to fail in their mathematical representation of the grounding line dynamics. Here, we present a 3-D full Stokes model of a marine ice sheet, in which the flow problem is coupled with the evolution of the upper and lower free surfaces, and the position of the grounding line determined by solving a contact problem between the shelf/sheet lower surface and the bedrock. Simulations are performed using the open-source finite-element code Elmer/Ice within a parallel environment. The effect of a pinning point, inserted beneath the ice shelf, on the ice dynamics is studied to demonstrate the model's ability to cope with curved and multiple grounding lines. Starting from a steady state, the sea level is slightly decreased to create a contact point between a seamount and the ice shelf. The model predicts a dramatic decrease of the shelf velocities, leading to an advance of the grounding line until both grounded zones merge together, during which an ice rumple forms above the contact area at the pinning point. Finally, we show that once the contact is created, increasing the sea level to its initial value does not cease the interaction with the pinning point and has no effect on the ice dynamics, indicating a stabilizing effect of pinning points.

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