The Potsdam Parallel Ice Sheet Model (PISM-PIK) – Part 2: Dynamic equilibrium simulation of the Antarctic ice sheet

Martin, Maria A.; Winkelmann, Ricarda; Haseloff, Marianne; Albrecht, Torsten; Bueler, Ed; Khroulev, C.; Levermann, Anders

doi:10.5194/tc-5-727-2011

Cited by 164 publications

(242 citation statements)

References 40 publications

(58 reference statements)

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“…The till friction angle is parameterized with bed elevation, as in ref. 42, and the basal pore water pressure is limited to a maximum fraction of 0.93 of the overburden pressure. This friction scheme ensures a continuous transition from quasi-nonslip regimes in elevated regions to the marine areas where basal resistance is low.…”

Section: Methodsmentioning

confidence: 99%

“…A linear interpolation of the freely evolving grounding line, and accordingly interpolated basal friction, enable realistic grounding-line motion also at medium to low horizontal resolution (32). Basal friction is calculated using a nonlinear Weertman-type sliding law (24) with a sliding exponent of 1/3 in combination with a Mohr-Coulomb model for plastic till (42,43) that accounts for the effect of evolving ice thickness and the associated change in overburden pressure on the basal till (44). The till friction angle is parameterized with bed elevation, as in ref.…”

Section: Methodsmentioning

confidence: 99%

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Collapse of the West Antarctic Ice Sheet after local destabilization of the Amundsen Basin

Feldmann

Levermann

2015

Proc. Natl. Acad. Sci. U.S.A.

181

152

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The future evolution of the Antarctic Ice Sheet represents the largest uncertainty in sea-level projections of this and upcoming centuries. Recently, satellite observations and high-resolution simulations have suggested the initiation of an ice-sheet instability in the Amundsen Sea sector of West Antarctica, caused by the last decades' enhanced basal ice-shelf melting. Whether this localized destabilization will yield a full discharge of marine ice from West Antarctica, associated with a global sea-level rise of more than 3 m, or whether the ice loss is limited by ice dynamics and topographic features, is unclear. Here we show that in the Parallel Ice Sheet Model, a local destabilization causes a complete disintegration of the marine ice in West Antarctica. In our simulations, at 5-km horizontal resolution, the region disequilibrates after 60 y of currently observed melt rates. Thereafter, the marine ice-sheet instability fully unfolds and is not halted by topographic features. In fact, the ice loss in Amundsen Sea sector shifts the catchment's ice divide toward the Filchner-Ronne and Ross ice shelves, which initiates grounding-line retreat there. Our simulations suggest that if a destabilization of Amundsen Sea sector has indeed been initiated, Antarctica will irrevocably contribute at least 3 m to global sea-level rise during the coming centuries to millennia.West Antarctic Ice Sheet | sea-level rise | tipping point | instability | marine ice-sheet instability T he Antarctic Ice Sheet is losing mass at an accelerating rate, and thus increasingly contributes to global sea-level rise (1,2). To what extent this is caused by anthropogenic warming of the atmosphere is unclear. The Amundsen Sea sector of West Antarctica accounts for the largest part of the ice loss, manifesting in a speed-up, thinning, and retreat of tributaries such as Pine Island Glacier and Thwaites Glacier during the last 4 decades (3-5). Large portions of the West Antarctic Ice Sheet (WAIS) are grounded on bedrock below sea level (6, 7). These so-called marine parts of the ice sheet hold an ice volume that would elevate global mean sea level by about 3.3 m (8). The bed below this marine ice is generally down-sloping in the inland direction. A grounding line (the line that separates the grounded ice sheet from the floating ice shelf) that is located on such bed has been shown to be potentially unstable (9, 10). The associated marine ice-sheet instability (i.e., self-sustained ice-sheet retreat) can be hindered by the buttressing of ice shelves, which has been investigated in different modeling frameworks (11)(12)(13)(14).The recently inferred destabilization of the Amundsen Sea sector coincides with an increase in the volume and temperature of relatively warm circumpolar deep water that reaches into the ice-shelf cavities in the Amundsen Sea (15, 16). The resulting substantially enhanced sub-ice-shelf melting facilitated the retreat of the grounding line of several tributaries onto the potentially unstable down-sloping bed section. Complex, high...

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Collapse of the West Antarctic Ice Sheet after local destabilization of the Amundsen Basin

Feldmann

Levermann

2015

Proc. Natl. Acad. Sci. U.S.A.

181

152

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“…They treated basal water pressure as a nonlinear function of water depth, capped at the overburden pressure. Martin et al (2011) assumed plastic flow with a yield stress proportional to N, with basal water pressure prescribed to be 96 % of overburden pressure under the marine portion of the Antarctic Ice Sheet (including close to grounding lines). This parameterization reduced but did not eliminate the discontinuity in basal friction at the grounding line.…”

Section: G R Leguy Et Al: Parameterization Of Basal Friction Nearmentioning

confidence: 99%

Parameterization of basal friction near grounding lines in a one-dimensional ice sheet model

2014

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Abstract. Ice sheets and ice shelves are linked by the transition zone, the region where flow dominated by vertical shear stress makes a transition to flow dominated by extensional stress. Adequate resolution of the transition zone is necessary for numerically accurate ice sheet-ice shelf simulations. The required resolution depends on how the basal physics is parameterized. We propose a new, simple parameterization of the effective pressure near the grounding line, combined with an existing friction law linking effective pressure to basal stress and sliding, in a one-dimensional, fixed-grid, vertically integrated model. This parameterization represents connectivity between the basal hydrological system and the ocean in the transition zone. Our model produces a smooth transition between finite basal friction in the ice sheet and zero basal friction in the ice shelf. In a set of experiments based on the Marine Ice Sheet Model Intercomparison Project (MISMIP), we show that with a smoother basal shear stress, the model yields accurate steady-state results at a fixed-grid resolution of ∼ 1 km.

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“…4; Fig. 2b of Martin et al 2011). The section towards the front thus displaces less water than its weight.…”

Section: The Calving Schemementioning

confidence: 99%

Verification of model simulated mass balance, flow fields and tabular calving events of the Antarctic ice sheet against remotely sensed observations

2012

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The Antarctic ice sheet (AIS) has the greatest potential for global sea level rise. This study simulates AIS ice creeping, sliding, tabular calving, and estimates the total mass balances, using a recently developed, advanced ice dynamics model, known as SEGMENT-Ice. SEGMENTIce is written in a spherical Earth coordinate system. Because the AIS contains the South Pole, a projection transfer is performed to displace the pole outside of the simulation domain. The AIS also has complex ice-watergranular material-bedrock configurations, requiring sophisticated lateral and basal boundary conditions. Because of the prevalence of ice shelves, a 'girder yield' type calving scheme is activated. The simulations of present surface ice flow velocities compare favorably with InSAR measurements, for various ice-water-bedrock configurations. The estimated ice mass loss rate during [2003][2004][2005][2006][2007][2008][2009] agrees with GRACE measurements and provides more spatial details not represented by the latter. The model estimated calving frequencies of the peripheral ice shelves from 1996 (roughly when the 5-km digital elevation and thickness data for the shelves were collected) to 2009 compare well with archived scatterometer images. SEG-MENT-Ice's unique, non-local systematic calving scheme is found to be relevant for tabular calving. However, the exact timing of calving and of iceberg sizes cannot be simulated accurately at present. A projection of the future mass change of the AIS is made, with SEGMENT-Ice forced by atmospheric conditions from three different coupled general circulation models. The entire AIS is estimated to be losing mass steadily at a rate of *120 km 3 /a at present and this rate possibly may double by year 2100.

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The Potsdam Parallel Ice Sheet Model (PISM-PIK) – Part 2: Dynamic equilibrium simulation of the Antarctic ice sheet

Cited by 164 publications

References 40 publications

Collapse of the West Antarctic Ice Sheet after local destabilization of the Amundsen Basin

Collapse of the West Antarctic Ice Sheet after local destabilization of the Amundsen Basin

Parameterization of basal friction near grounding lines in a one-dimensional ice sheet model

Verification of model simulated mass balance, flow fields and tabular calving events of the Antarctic ice sheet against remotely sensed observations

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