Processes controlling the downstream evolution of ice rheology in glacier shear margins: case study on Rutford Ice Stream, West Antarctica

Minchew, Brent; Meyer, Colin R.; Robel, Alexander; Gudmundsson, G. Hilmar; Simons, M.

doi:10.1017/jog.2018.47

Cited by 76 publications

(77 citation statements)

References 96 publications

(203 reference statements)

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“…We, however, take A to be constant and equal to the value expected for temperate ice, which allows us to estimate the shear heating from the data. Evaluating A at the melting temperature, moreover, represents the minimum expected shear heating excluding the effects of fabric and porosity Minchew et al, 2018). Thus, our model results are robust to this simplification.…”

Section: Application To the Southern Bindschadler Shear Marginmentioning

confidence: 59%

A Model for the Downstream Evolution of Temperate Ice and Subglacial Hydrology Along Ice Stream Shear Margins

et al. 2018

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Antarctic mass balance and contribution to sea level rise are dominated by the flow of ice through narrow conduits called ice streams. These regions of relatively fast flow drain over 90% of the ice sheet and generate significant amounts of frictional heat at the ice stream margins where there is a transition to slow flow in the ridge. This heat can generate temperate ice and a sharp transition in flow speed between the stream and the ridge. Within zones of temperate ice, meltwater is produced and drains to the bed. Here we model the downstream development of a temperate zone along an ice stream shear margin and the flow of meltwater through temperate ice into a subglacial hydrologic system. The hydrology sets the basal effective pressure, defined as the difference between ice overburden and water pressure. Using the southern shear margin of Bindschadler Ice Stream as a case study, our model results indicate an abrupt transition from a distributed to channelized hydrologic system within a few ice thicknesses of the point where the temperate zone initiates. This transition leads to a strengthening of the till due to reduced pore pressure because the water pressure in the channel is lower than in the distributed system, a potential mechanism by which hydrology can prevent lateral migration of shear margins.

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Section: Application To the Southern Bindschadler Shear Marginmentioning

confidence: 59%

A Model for the Downstream Evolution of Temperate Ice and Subglacial Hydrology Along Ice Stream Shear Margins

et al. 2018

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“…In addition, plots of the norm of the basal shear stress obtained for the three inferred states are included in the Supplement (Fig. S1) to allow for a comparison with previous work in which inversions of basal shear stress in the regions of PIG and Thwaites were performed (Joughin et al, 2009;Morlighem et al, 2010). At the end of the inversions, there are several regions where the local driving stress is not entirely compensated by the local basal shear stress (blue regions).…”

Section: Initialisationmentioning

confidence: 99%

“…These soft bands correspond to shear margins, where high shear stresses induce a local reduction of ice viscosity through different physical processes, including damage, strain heating and the development of crystalline fabric (e.g. Borstad et al, 2013;Bondzio et al, 2017;Minchew et al, 2018). On the contrary, the inversion algorithm can render the ice locally stiffer in order to decrease the modelled velocities in areas where they are too high compared to the observations, which is typically the case for ice shelves.…”

Section: Initialisationmentioning

confidence: 99%

“…Gradientbased optimisation methods are routinely used to estimate uncertain model parameter fields and boundary conditions so that the initial ice-sheet geometry and surface velocity field are as close as possible to the observations (e.g. Morlighem et al, 2010Morlighem et al, , 2013Gillet-Chaulet et al, 2012;Cornford et al, 2015). Although such methods enable us to deduce the current basal shear stress field from observed surface velocities, the form of the friction law cannot be discriminated with a unique set of observations (Joughin et al, 2004;Gillet-Chaulet et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

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Sensitivity of centennial mass loss projections of the Amundsen basin to the friction law

2019

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Abstract. Reliable projections of ice sheets' future contributions to sea-level rise require models that are able to accurately simulate grounding-line dynamics, starting from initial states consistent with observations. Here, we simulate the centennial evolution of the Amundsen Sea Embayment in response to a prescribed perturbation in order to assess the sensitivity of mass loss projections to the chosen friction law, depending on the initialisation strategy. To this end, three different model states are constructed by inferring both the initial basal shear stress and viscosity fields with various relative weights. Then, starting from each of these model states, prognostic simulations are carried out using a Weertman, a Schoof and a Budd friction law, with different parameter values. Although the sensitivity of projections to the chosen friction law tends to decrease when more weight is put on viscosity during initialisation, it remains significant for the most physically acceptable of the constructed model states. Independently of the considered model state, the Weertman law systematically predicts the lowest mass losses. In addition, because of its particular dependence on effective pressure, the Budd friction law induces significantly different grounding-line retreat patterns than the other laws and predicts significantly higher mass losses.

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“…Although mass density cannot vary more than 25% and n should be approximately 3,Ṁ and A can vary independently by orders of magnitude. Thus, the balance driving stress, τ d * , for an idealized glacier is determined primarily byṀ /A, the ratio of mass balance,Ṁ , to the rate factor, A, the latter of which depends on ice temperature and interstitial meltwater content, along with crystallographic fabric [104].…”

Section: (B) Implications Of Surge Mechanicsmentioning

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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Processes controlling the downstream evolution of ice rheology in glacier shear margins: case study on Rutford Ice Stream, West Antarctica

Cited by 76 publications

References 96 publications

A Model for the Downstream Evolution of Temperate Ice and Subglacial Hydrology Along Ice Stream Shear Margins

A Model for the Downstream Evolution of Temperate Ice and Subglacial Hydrology Along Ice Stream Shear Margins

Sensitivity of centennial mass loss projections of the Amundsen basin to the friction law

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

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