The role of crystal fabric in flow near an ice divide

Pettit, E. C.; Þorsteinsson, Þorsteinn; Jacobson, H. Paul; Waddington, Edwin D.

doi:10.3189/172756507782202766

Cited by 66 publications

(93 citation statements)

References 51 publications

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“…C-axes rotate during the deformation towards the main direction of compression and away from the tensional direction ( Van der Veen and Whillans, 1994). Consequently, the resulted anisotropy of the ice will affect the flow of ice (Gagliardini and Meyssonnier, 2000;Mangeney et al, 1997;Pettit et al, 2007). We can thus qualitatively compare the fabric evolution with the reconstructed thinning function, to look for possibly common patterns.…”

Section: Thinning Functionmentioning

confidence: 99%

TALDICE-1 age scale of the Talos Dome deep ice core, East Antarctica

Buiron¹,

Chappellaz²,

Stenni

et al. 2011

Clim. Past

104

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Abstract.A new deep ice core drilling program, TALDICE, has been successfully handled by a European team at Talos Dome, in the Ross Sea sector of East Antarctica, down to 1620 m depth. Using stratigraphic markers and a new inverse method, we produce the first official chronology of the ice core, called TALDICE-1. We show that it notably improves an a priori chronology resulting from a one-dimensional ice flow model. It is in agreement with a posteriori controls of the resulting accumulation rate and thinning function along the core. An absolute uncertainty of only 300 yr is obtained over the course of the last deglaciation. This uncertainty remains lower than 600 yr over Marine Isotope Stage 3, back to 50 kyr BP. The phasing of the TALDICE ice core climate record with respect to the central East Antarctic plateau and Greenland records can thus be determined with a precision allowing for a discussion of the mechanisms at work at submillennial time scales.

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Section: Thinning Functionmentioning

confidence: 99%

TALDICE-1 age scale of the Talos Dome deep ice core, East Antarctica

Buiron¹,

Chappellaz²,

Stenni

et al. 2011

Clim. Past

104

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“…This leads to an apparent upwarping of the isochronous layers. The development and influence of anisotropic fabric on the flow of ice at divides and the effects on the development of Raymond bumps were investigated 368 A. Diez and O. Eisen: Seismic wave propagation in anisotropic ice -Part 1 by, for instance, Pettit et al (2007) and Martín et al (2009a). At ice divides features like double bumps and synclines are observed (Drews et al, 2013), next to single bumps.…”

Section: Introductionmentioning

confidence: 99%

Seismic wave propagation in anisotropic ice – Part 1: Elasticity tensor and derived quantities from ice-core properties

Diez

Eisen

2015

The Cryosphere

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Abstract.A preferred orientation of the anisotropic ice crystals influences the viscosity of the ice bulk and the dynamic behaviour of glaciers and ice sheets. Knowledge about the distribution of crystal anisotropy is mainly provided by crystal orientation fabric (COF) data from ice cores. However, the developed anisotropic fabric influences not only the flow behaviour of ice but also the propagation of seismic waves. Two effects are important: (i) sudden changes in COF lead to englacial reflections, and (ii) the anisotropic fabric induces an angle dependency on the seismic velocities and, thus, recorded travel times. A framework is presented here to connect COF data from ice cores with the elasticity tensor to determine seismic velocities and reflection coefficients for cone and girdle fabrics. We connect the microscopic anisotropy of the crystals with the macroscopic anisotropy of the ice mass, observable with seismic methods. Elasticity tensors for different fabrics are calculated and used to investigate the influence of the anisotropic ice fabric on seismic velocities and reflection coefficients, englacially as well as for the ice-bed contact. Hence, it is possible to remotely determine the bulk ice anisotropy.

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“…The plastic anisotropy can have a considerable influence on the bulk deformation rate and vice versa. Hence, it is desirable to incorporate the development of anisotropy in flow models (Pettit et al, 2007;Seddik et al, 2008;Martin et al, 2009;Graham et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Deriving micro- to macro-scale seismic velocities from ice-core <i>c</i> axis orientations

et al. 2018

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Abstract. One of the great challenges in glaciology is the ability to estimate the bulk ice anisotropy in ice sheets and glaciers, which is needed to improve our understanding of ice-sheet dynamics. We investigate the effect of crystal anisotropy on seismic velocities in glacier ice and revisit the framework which is based on fabric eigenvalues to derive approximate seismic velocities by exploiting the assumed symmetry. In contrast to previous studies, we calculate the seismic velocities using the exact c axis angles describing the orientations of the crystal ensemble in an icecore sample. We apply this approach to fabric data sets from an alpine and a polar ice core. Our results provide a quantitative evaluation of the earlier approximative eigenvalue framework. For near-vertical incidence our results differ by up to 135 m s −1 for P-wave and 200 m s −1 for S-wave velocity compared to the earlier framework (estimated 1 % difference in average P-wave velocity at the bedrock for the short alpine ice core). We quantify the influence of shearwave splitting at the bedrock as 45 m s −1 for the alpine ice core and 59 m s −1 for the polar ice core. At non-vertical incidence we obtain differences of up to 185 m s −1 for P-wave and 280 m s −1 for S-wave velocities. Additionally, our findings highlight the variation in seismic velocity at non-vertical incidence as a function of the horizontal azimuth of the seismic plane, which can be significant for non-symmetric orientation distributions and results in a strong azimuth-dependent shear-wave splitting of max. 281 m s −1 at some depths. For a given incidence angle and depth we estimated changes in phase velocity of almost 200 m s −1 for P wave and more than 200 m s −1 for S wave and shear-wave splitting under a rotating seismic plane. We assess for the first time the change in seismic anisotropy that can be expected on a short spatial (vertical) scale in a glacier due to strong variability in crystalorientation fabric (±50 m s −1 per 10 cm). Our investigation of seismic anisotropy based on ice-core data contributes to advancing the interpretation of seismic data, with respect to extracting bulk information about crystal anisotropy, without having to drill an ice core and with special regard to future applications employing ultrasonic sounding.

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The role of crystal fabric in flow near an ice divide

Cited by 66 publications

References 51 publications

TALDICE-1 age scale of the Talos Dome deep ice core, East Antarctica

TALDICE-1 age scale of the Talos Dome deep ice core, East Antarctica

Seismic wave propagation in anisotropic ice – Part 1: Elasticity tensor and derived quantities from ice-core properties

Deriving micro- to macro-scale seismic velocities from ice-core <i>c</i> axis orientations

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The role of crystal fabric in flow near an ice divide

Cited by 66 publications

References 51 publications

TALDICE-1 age scale of the Talos Dome deep ice core, East Antarctica

TALDICE-1 age scale of the Talos Dome deep ice core, East Antarctica

Seismic wave propagation in anisotropic ice – Part 1: Elasticity tensor and derived quantities from ice-core properties

Deriving micro- to macro-scale seismic velocities from ice-core &lt;i&gt;c&lt;/i&gt; axis orientations

Contact Info

Product

Resources

About

Deriving micro- to macro-scale seismic velocities from ice-core <i>c</i> axis orientations