Modeling Ice‐Crystal Fabric as a Proxy for Ice‐Stream Stability

Lilien, David A.; Rathmann, Nicholas; Hvidberg, Christine S.; Dahl‐Jensen, Dorthe

doi:10.1029/2021jf006306

Cited by 17 publications

(36 citation statements)

References 99 publications

(185 reference statements)

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“…The advection of the shear margins during the flow of ice from land to sea can result in bands of strongly deformed ice that transect ice shelves (LeDoux et al, 2017) and can potentially affect the stability of ice shelves. Modelling suggests that remnant CPO resultant in shear margins can be present 10000 years after advection downstream (Lilien et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

Ultrasonic and seismic constraints on crystallographic preferred orientations of the Priestley Glacier shear margin, Antarctica

Lutz

Prior

Still

et al. 2022

Preprint

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Abstract. Crystallographic preferred orientations (CPOs) are particularly important in controlling the mechanical properties of glacial shear margins. Logistical and safety considerations often make direct sampling of shear margins difficult and geophysical measurements are commonly used to constrain the CPOs. We present here the first direct comparison of seismic and ultrasonic data with measured CPOs in a polar shear margin. The measured CPO from ice samples from a 58 m deep borehole in the left lateral shear margin of the Priestley Glacier, Antarctica, is dominated by horizontal c-axes aligned sub-perpendicular to flow. A vertical seismic profile experiment with hammer shots up to 50 m away from the borehole, in four different azimuthal directions, shows velocity anisotropy of both P-waves and S-waves. Matching P-wave data to the anisotropy corresponding to CPO models defined by horizontally aligned c-axes gives two possible solutions for c-axis azimuth, one of which matches the c-axis measurements. If both P-wave and S-wave data are used, there is one best fit for azimuth and intensity of c-axis alignment that matches well the measurements. Azimuthal P-wave and S-wave ultrasonic data recorded in the laboratory on the ice core show clear anisotropy that matches that predicted from the CPO of the samples. With good quality data, azimuthal increments of 30° or less will constrain well the orientation and intensity of c-axis alignment. Our experiments provide a good framework for planning seismic surveys aimed at constraining the anisotropy of shear margins.

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Section: Introductionmentioning

confidence: 99%

Ultrasonic and seismic constraints on crystallographic preferred orientations of the Priestley Glacier shear margin, Antarctica

Lutz

Prior

Still

et al. 2022

Preprint

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“…As another example, Lilien et al. (2021) recently modeled the strain‐induced rotation of c ‐axes inside an idealized ice stream, finding that fabrics may tilt at least 8° under a combination of extensional flow and vertical shear. Such tilt angles have also been suggested to exist below or near ice divides (Martín et al., 2009).…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, fabric anisotropy provides a unique constraint on the past and present deformation in the lithosphere and sublithospheric mantle (Fouch & Rondenay, 2006). Likewise, in the limit of weak dynamic recrystallization, ice fabrics might provide a proxy for past and present flow regimes (Thorsteinsson et al., 2003; Wilson & Peternell, 2011) that could reveal the existence of paleo ice streams (Lilien et al., 2021; Llorens et al., 2021).…”

Section: Introductionmentioning

confidence: 99%

“…For vertical shear with active discontinuous dynamic recrystallization, the otherwise vertical principal direction (center of orientation mass) may hence be displaced toward the horizontal plane. As another example, Lilien et al (2021) recently modeled the strain-induced rotation of c-axes inside an idealized ice stream, finding that fabrics may tilt at least 8° under a combination of extensional flow and vertical shear. Such tilt angles have also been suggested to exist below or near ice divides (Martín et al, 2009).…”

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confidence: 99%

“…

Thus, as the crystal orientation fabric (henceforth fabric) evolves during flow in polycrystalline glacier ice or in the mineral aggregate of the upper mantle, so should the bulk directional viscosity and elasticity structure. Being able to infer fabrics in situ is central for validating largescale anisotropic ice-flow models and geodynamical models of mantle flow processes; models that might lead to a better understanding of, for example, streaming ice (Lilien et al, 2021) and the coupling between plate motions and the sublithospheric mantle (e.g., W. Wang & Becker, 2019), respectively. Furthermore, fabric anisotropy provides a unique constraint on the past and present deformation in the lithosphere and sublithospheric mantle (Fouch & Rondenay, 2006).

…”

mentioning

confidence: 99%

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On the Limitations of Using Polarimetric Radar Sounding to Infer the Crystal Orientation Fabric of Ice Masses

Rathmann

Lilien

Grinsted

et al. 2022

Geophysical Research Letters

Self Cite

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Thus, as the crystal orientation fabric (henceforth fabric) evolves during flow in polycrystalline glacier ice or in the mineral aggregate of the upper mantle, so should the bulk directional viscosity and elasticity structure. Being able to infer fabrics in situ is central for validating largescale anisotropic ice-flow models and geodynamical models of mantle flow processes; models that might lead to a better understanding of, for example, streaming ice (Lilien et al., 2021) and the coupling between plate motions and the sublithospheric mantle (e.g., W. Wang & Becker, 2019), respectively. Furthermore, fabric anisotropy provides a unique constraint on the past and present deformation in the lithosphere and sublithospheric mantle (Fouch & Rondenay, 2006). Likewise, in the limit of weak dynamic recrystallization, ice fabrics might provide a proxy for past and present flow regimes (

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On the nonlinear viscosity of the orthotropic bulk rheology

Rathmann

Lilien

2022

J. Glaciol.

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We compare different ways the bulk flow nonlinearity of glacier ice can be captured in an orthotropic rheology. Specifically, we compare the unapproximated orthotropic rheology, derived from plastic potential theory, to existing approximations that assume either the nonlinear viscosity or fluidity is identical to that of Glen's isotropic flow law. We find, overall, a reasonable agreement between the three orthotropic rheologies, and with existing Dye 3 ice-core deformation tests, although assuming Glen's viscosity provides the best approximation to the unapproximated rheology. Our results therefore suggest that previous studies based on either approximation to the orthotropic rheology are on relatively safe ground in the sense that both approximations generally agree with the unapproximated rheology and experimental data. Finally, we provide the forward and inverse analytical forms of all three rheologies for use in future numerical ice-flow modelling.

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Modeling Ice‐Crystal Fabric as a Proxy for Ice‐Stream Stability

Abstract: The crystal structure of glaciers and ice sheets records past flow and affects present-day ice deformation. Much work on ice-crystal orientation fabric has focused on the fabric's effect upon deformation (e.g.

Cited by 17 publications

References 99 publications

Ultrasonic and seismic constraints on crystallographic preferred orientations of the Priestley Glacier shear margin, Antarctica

Ultrasonic and seismic constraints on crystallographic preferred orientations of the Priestley Glacier shear margin, Antarctica

On the Limitations of Using Polarimetric Radar Sounding to Infer the Crystal Orientation Fabric of Ice Masses

On the nonlinear viscosity of the orthotropic bulk rheology

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