Regularized Coulomb Friction Laws for Ice Sheet Sliding: Application to Pine Island Glacier, Antarctica

Joughin, Ian; Smith, B. E.; Schoof, Christian

doi:10.1029/2019gl082526

Cited by 134 publications

(242 citation statements)

References 38 publications

(67 reference statements)

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“…Recent work shows that alternatively parameterized versions of Equation 1 (regularized Coulomb friction) extend plastic behavior much farther inland to yield better agreement with observations on Pine Island Glacier (Joughin et al, 2019). The friction law in Equation 1 relies on a height-above-flotation parameterization for effective pressure, which limits Coulomb (plastic) behavior to near the grounding line.…”

Section: Model Complexitymentioning

confidence: 99%

“…We take = 3, and assume that the effective pressure is equal to the ice overburden minus the hydrostatic pressure. With this assumption, Coulomb-like behavior only occurs within several kilometers of the grounding line, with Weertman-like behavior farther inland (Joughin et al, 2019). This assumption is valid if a drainage system connects every point on the glacier bed to the ocean, which is…”

Section: Prognostic Simulationsmentioning

confidence: 99%

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Melt at grounding line controls observed and future retreat of Smith, Pope, and Kohler Glaciers

Lilien¹,

Joughin²,

Smith³

et al. 2019

Preprint

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Abstract. Smith, Pope, and Kohler Glaciers and the corresponding Crosson and Dotson Ice Shelves have undergone speedup, thinning, and rapid grounding-line retreat in recent years, leaving them in a state likely conducive to future retreat. We conducted a suite of numerical model simulations of these glaciers and compared the results to observations to determine the processes controlling their recent evolution. The model simulations indicate that the state of these glaciers in the 1990s was not inherently unstable, i.e. that small perturbations to the grounding line would not necessarily have caused the large retreat that has been observed. Instead, sustained, elevated melt at the grounding line was needed to cause the observed retreat. Weakening of the margins of Crosson Ice Shelf may have hastened the onset of grounding-line retreat but is unlikely to have initiated these rapid changes without an accompanying increase in melt. In the simulations that most closely match the observed thinning, speedup, and retreat, modeled grounding-line retreat and ice loss continue unabated throughout the 21st century, and subsequent retreat along Smith Glacier’s trough appears likely. Given the rapid progression of grounding-line retreat in the model simulations, thinning associated with the retreat of Smith Glacier may reach the ice divide and undermine a portion of the Thwaites catchment as quickly as changes initiated at the Thwaites terminus.

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Section: Model Complexitymentioning

confidence: 99%

Section: Prognostic Simulationsmentioning

confidence: 99%

Melt at grounding line controls observed and future retreat of Smith, Pope, and Kohler Glaciers

Lilien¹,

Joughin²,

Smith³

et al. 2019

Preprint

Self Cite

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“…2.23 is consistent with the so-called regularized-Coulomb sliding law, which has recently emerged as a candidate for a universal form of the sliding law, because in this work, we are focused on the skin-friction regime defined by Eq. 2.1 [74,82,83,99].…”

Section: (C) Basal Slip Accelerationmentioning

confidence: 99%

Dilation of subglacial sediment governs incipient surge motion in glaciers with deformable beds

Minchew¹,

Meyer²

2020

Preprint

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Glacier surges are quasi-periodic episodes of rapid ice flow that arise from increases in slip-rate at the ice-bed interface. The mechanisms that trigger and sustain surges are not well-understood. Here, we develop a new model of incipient surge motion for glaciers underlain by sediments to explore how surges may arise from slip instabilities within a thin layer of saturated, deforming subglacial till. Our model represents the evolution of internal friction, porosity, and pore water pressure within the till as functions of the rate and history of shear deformation, and couples the till mechanics to a simple ice-flow model. Changes in pore water pressure govern incipient surge motion, with less-permeable till facilitating surging because dilation-driven reductions in pore-water pressure slow the rate at which till tends toward a new steady-state, thereby allowing time for the glacier to thin dynamically. The reduction of overburden (and thus effective) pressure at the bed caused by dynamic thinning of the glacier sustains surge acceleration in our model. The need for changes in both the hydromechanical properties of the till and thickness of the glacier creates restrictive conditions for surge motion that are consistent with the rarity of surge-type glaciers and their geographic clustering.

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“…We focused on a linear viscous friction law commonly used in other studies (Morlighem et al, 2013;Quiquet et al, 2018;Alvarez-Solas et al, 2019). We are aware that other types of friction laws could have been tested, such as a regularized Coulomb law (Joughin et al, 2019) or a Coulomb-plastic behaviour (Nowicki et al, 2013), typically for ice flowing over a bedrock filled with cavities.…”

Section: Basal Dragging Lawmentioning

confidence: 99%

“…Generally, basal stress follows either a power-law formulation on the basal ice velocity (a special case being the Weertman (1957) friction law) or a Coulomb friction law (Schoof, 2005) with different power-law coefficients, a friction coefficient and potentially a regularization term. Ice-sheet models thus use friction formulations that can range from linear viscous and regularized Coulomb friction laws, typical of hard bedrock sliding (Larour et al, 2012;Pattyn et al, 2013;Joughin et al, 2019) to Coulomb-plastic deformation, characteristic of ice flow over a soft bedrock with filled cavities (Schoof, 2005(Schoof, , 2006Nowicki et al, 2013). In the simplest cases a constant friction coefficient is prescribed over the whole domain (Golledge et al, 2012), but generally this parameter incorporates the dependency of basal friction on the effective pressure exerted by the ice, as well as on bedrock characteristics by making use of assumed till properties (Winkelmann et al, 2011;Albrecht et al, 2019;Sutter et al, 2019) or basal temperature conditions (Pattyn, 2017;Quiquet et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Exploring the impact of atmospheric forcing and basal boundary conditions on the simulation of the Antarctic ice sheet at the Last Glacial Maximum

Blasco

Álvarez-Solas

Robinson

et al. 2020

Preprint

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Abstract. Little is known about the distribution of ice in the Antarctic ice sheet (AIS) during the Last Glacial Maximum (LGM). Whereas marine and terrestrial geological data indicate that the grounded ice advanced to a position close to the continental-shelf break, the total ice volume is unclear. Glacial boundary conditions are potentially important sources of uncertainty, in particular basal friction and climatic boundary conditions. Basal friction exerts a strong control on the large-scale dynamics of the ice sheet and thus affects its size, and is not well constrained. Glacial climatic boundary conditions determine the net accumulation and ice temperature, and are also poorly known. Here we explore the effect of the uncertainty in both features on the total simulated ice storage of the AIS at the LGM. For this purpose we use a hybrid ice-sheet-shelf model that is forced with different basal-drag choices and glacial background climatic conditions obtained from the LGM ensemble climate simulations of the third phase of the Paleoclimate Modelling Intercomparison Project (PMIP3). For a wide range of plausible basal friction configurations, the simulated ice dynamics vary widely but all simulations produce fully extended ice sheets towards the continental-shelf break. More dynamically active ice sheets correspond to lower ice volumes, while they remain consistent with the available constraints on ice extent. Thus, this work points to the possibility of an AIS with very active ice streams during the LGM. In addition, we find that the surface boundary temperature field plays a crucial role in determining the ice extent through its effect on viscosity. For ice sheets of a similar extent and comparable dynamics, we find that the precipitation field determines the total AIS volume. However, precipitation is deeply uncertain. Climatic fields simulated by climate models show more precipitation in coastal regions than a spatially uniform anomaly, which can lead to larger ice volumes. We strongly support using these paleoclimatic fields to simulate and study the LGM and potentially other time periods like the Last Interglacial. However, their accuracy must be assessed as well, as differences between climate model forcing lead to a range in the simulated ice volume and extension of about 6 m sea-level equivalent and one million km2.

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Regularized Coulomb Friction Laws for Ice Sheet Sliding: Application to Pine Island Glacier, Antarctica

Cited by 134 publications

References 38 publications

Melt at grounding line controls observed and future retreat of Smith, Pope, and Kohler Glaciers

Melt at grounding line controls observed and future retreat of Smith, Pope, and Kohler Glaciers

Dilation of subglacial sediment governs incipient surge motion in glaciers with deformable beds

Exploring the impact of atmospheric forcing and basal boundary conditions on the simulation of the Antarctic ice sheet at the Last Glacial Maximum

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