scholarly journals Ice shelf fracture parameterization in an ice sheet model

2017 ◽  
Author(s):  
Sainan Sun ◽  
Stephen Cornford ◽  
Rupert Gladstone ◽  
Liyun Zhao ◽  
John Moore
Keyword(s):  
Fracture Process ◽  
Large Scale ◽  
Damage Model ◽  
Ice Sheet ◽  
Continuum Damage ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Continuum Damage Model ◽  
Grounding Line ◽  
Fracture Processes

Abstract. Floating ice shelves exert a stabilizing force onto the inland ice sheet. However, this buttressing effect is diminished by the fracture process, which on large scales effectively softens the ice, accelerating its flow, increasing calving, and potentially leading to ice shelf breakup. Here, we explore how the application of a continuum damage model (CDM) to the prognostic ice sheet model BISICLES can account for the effects of fracture processes on viscous ice dynamics. Damage is created by the local stress field and advects downstream. This continuum damage model is coupled to the dynamical ice flow model by decreasing the effective viscosity proportional to the damage field. To evaluate the physical role of the fracture process on large-scale ice sheet dynamics and also discern the relative importance of the parameters used in the damage model, we carry out a suite of numerical experiments based on the MISMIP+ (Marine Ice Sheet Model Intercomparison Project) marine ice sheet geometry. We find that behavior of the simulated marine ice sheet is sensitive to fracture processes on the ice shelf. In the case of a geometry that produces strong lateral stress, the stiffness of ice around the grounding line is essential to ice sheet evolution, with softer or more damaged ice leading to thinning and grounding line retreat.

scholarly journals Ice shelf fracture parameterization in an ice sheet model

2017 ◽  
Vol 11 (6) ◽  
pp. 2543-2554 ◽  
Author(s):  
Sainan Sun ◽  
Stephen L. Cornford ◽  
John C. Moore ◽  
Rupert Gladstone ◽  
Liyun Zhao
Keyword(s):  
Enhancement Factor ◽  
Large Scale ◽  
Damage Model ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Shelves ◽  
Order Of Magnitude ◽  
Eventual Loss ◽  
Spatially Varying

Abstract. Floating ice shelves exert a stabilizing force onto the inland ice sheet. However, this buttressing effect is diminished by the fracture process, which on large scales effectively softens the ice, accelerating its flow, increasing calving, and potentially leading to ice shelf breakup. We add a continuum damage model (CDM) to the BISICLES ice sheet model, which is intended to model the localized opening of crevasses under stress, the transport of those crevasses through the ice sheet, and the coupling between crevasse depth and the ice flow field and to carry out idealized numerical experiments examining the broad impact on large-scale ice sheet and shelf dynamics. In each case we see a complex pattern of damage evolve over time, with an eventual loss of buttressing approximately equivalent to halving the thickness of the ice shelf. We find that it is possible to achieve a similar ice flow pattern using a simple rule of thumb: introducing an enhancement factor ∼ 10 everywhere in the model domain. However, spatially varying damage (or equivalently, enhancement factor) fields set at the start of prognostic calculations to match velocity observations, as is widely done in ice sheet simulations, ought to evolve in time, or grounding line retreat can be slowed by an order of magnitude.

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 Geometry and ice dynamics of the Darwin–Hatherton glacial system, Transantarctic Mountains

2017 ◽  
Vol 63 (242) ◽  
pp. 959-972
Author(s):  
METTE K. GILLESPIE ◽  
WENDY LAWSON ◽  
WOLFGANG RACK ◽  
BRIAN ANDERSON ◽  
DONALD D. BLANKENSHIP ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Ross Ice Shelf ◽  
Basal Ice ◽  
Grounding Line ◽  
Ice Flows ◽  
Ice Velocity ◽  
The Mean

ABSTRACTThe Darwin–Hatherton Glacial system (DHGS) connects the East Antarctic Ice Sheet (EAIS) with the Ross Ice Shelf and is a key area for understanding past variations in ice thickness of surrounding ice masses. Here we present the first detailed measurements of ice thickness and grounding zone characteristics of the DHGS as well as new measurements of ice velocity. The results illustrate the changes that occur in glacier geometry and ice flux as ice flows from the polar plateau and into the Ross Ice Shelf. The ice discharge and the mean basal ice shelf melt for the first 8.5 km downstream of the grounding line amount to 0.24 ± 0.05 km3 a−1 and 0.3 ± 0.1 m a−1, respectively. As the ice begins to float, ice thickness decreases rapidly and basal terraces develop. Constructed maps of glacier geometry suggest that ice drainage from the EAIS into the Darwin Glacier occurs primarily through a deep subglacial canyon. By contrast, ice thins to <200 m at the head of the much slower flowing Hatherton Glacier. The glaciological field study establishes an improved basis for the interpretation of glacial drift sheets at the link between the EAIS and the Ross Ice Sheet.

An updated continuum damage model to investigate fracture process of structures in DBTT region

2008 ◽  
Vol 151 (2) ◽  
pp. 199-215 ◽  
Author(s):  
Zhao-Xi Wang ◽  
Jian Lu ◽  
Hui-Ji Shi ◽  
Dong-Feng Li ◽  
Xianfeng Ma
Keyword(s):  
Fracture Process ◽  
Damage Model ◽  
Continuum Damage ◽  
Continuum Damage Model

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.

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 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 Shear-margin melting causes stronger transient ice discharge than ice-stream melting according to idealized simulations

2021 ◽  
Author(s):  
Johannes Feldmann ◽  
Ronja Reese ◽  
Ricarda Winkelmann ◽  
Anders Levermann
Keyword(s):  
Three Dimensional ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Ice Shelves ◽  
Ice Stream ◽  
Future Global Warming ◽  
Grounding Line ◽  
Fast Flow ◽  
Basal Melting

Abstract. Basal ice-shelf melting is the key driver of Antarctica's increasing sea-level contribution. In diminishing the buttressing force of the ice shelves that fringe the ice sheet the melting increases the solid-ice discharge into the ocean. Here we contrast the influence of basal melting in two different ice-shelf regions on the time-dependent response of an idealized, inherently buttressed ice-sheet-shelf system. Carrying out three-dimensional numerical simulations, the basal-melt perturbations are applied close to the grounding line in the ice-shelf's 1) ice-stream region, where the ice shelf is fed by the fastest ice masses that stream through the upstream bed trough and 2) shear margins, where the ice flow is slower. The results show that melting below one or both of the shear margins can cause a decadal to centennial increase in ice discharge that is more than twice as large compared to a similar perturbation in the ice-stream region. We attribute this to the fact that melt-induced ice-shelf thinning in the central grounding-line region is attenuated very effectively by the fast flow of the central ice stream. In contrast, the much slower ice dynamics in the lateral shear margins of the ice shelf facilitate sustained ice-shelf thinning and thereby foster buttressing reduction. Regardless of the melt location, a higher melt concentration toward the grounding line generally goes along with a stronger response. Our results highlight the vulnerability of outlet glaciers to basal melting in stagnant, buttressing-relevant ice-shelf regions, a mechanism that may gain importance under future global warming.

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

2012 ◽  
Vol 6 (1) ◽  
pp. 101-112 ◽  
Author(s):  
L. Favier ◽  
O. Gagliardini ◽  
G. Durand ◽  
T. Zwinger
Keyword(s):  
Sea Level ◽  
Contact Point ◽  
Ice Sheet ◽  
Lower Surface ◽  
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, which is 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 ice sheet models use simplifications of the flow equations, as they do not include all the stress components, and are known to fail in their 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 is 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 model's ability to cope with a curved grounding line and the effect of a pinning point beneath the ice shelf are investigated through prognostic simulations. 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 release the pinning point and has no effect on the ice dynamics, indicating a stabilising effect of pinning points.

scholarly journals Dynamical processes involved in the retreat of marine ice sheets

2001 ◽  
Vol 47 (157) ◽  
pp. 271-282 ◽  
Author(s):  
Richard C.A. Hindmarsh ◽  
E. Le Meur
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Streams ◽  
Antarctic Ice Sheet ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
Grounding Line ◽  
Neutral Equilibrium ◽  
Generally True

AbstractMarine ice sheets with mechanics described by the shallow-ice approximation by definition do not couple mechanically with the shelf. Such ice sheets are known to have neutral equilibria. We consider the implications of this for their dynamics and in particular for mechanisms which promote marine ice-sheet retreat. The removal of ice-shelf buttressing leading to enhanced flow in grounded ice is discounted as a significant influence on mechanical grounds. Sea-level rise leading to reduced effective pressures under ice streams is shown to be a feasible mechanism for producing postglacial West Antarctic ice-sheet retreat but is inconsistent with borehole evidence. Warming thins the ice sheet by reducing the average viscosity but does not lead to grounding-line retreat. Internal oscillations either specified or generated via a MacAyeal–Payne thermal mechanism promote migration. This is a noise-induced drift phenomenon stemming from the neutral equilibrium property of marine ice sheets. This migration occurs at quite slow rates, but these are sufficiently large to have possibly played a role in the dynamics of the West Antarctic ice sheet after the glacial maximum. Numerical experiments suggest that it is generally true that while significant changes in thickness can be caused by spatially uniform changes, spatial variability coupled with dynamical variability is needed to cause margin movement.

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