Simulating higher-order fabric structure in a coupled, anisotropic ice-flow model: application to Dome C

Lilien, David A.; Rathmann, Nicholas M.; Hvidberg, Christine S.; Grinsted, Aslak; Ershadi, M. Reza; Drews, Reinhard; Dahl-Jensen, Dorthe

doi:10.1017/jog.2023.78

Cited by 4 publications

(1 citation statement)

References 94 publications

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“…A more complex model could take into account the effects of anisotropy, as Seddik et al (2011) showed for the Dome Fuji region. Multiple anisotropic modelling efforts used idealised (Gillet-Chaulet et al, 2005;Gillet-Chaulet, 2006) or observed (Lilien et al, 2023) topography to examine how crystal fabric might affect flow around DC, finding notable changes to the flow field as a result of the crystal fabric. However, these more complex models are not easily differentiated to permit their use in arbitrary inverse problems and are currently too computationally costly to run in an inverse framework like that used here.…”

Section: Agementioning

confidence: 99%

Age, thinning and spatial origin of the Beyond EPICA ice from a 2.5D ice flow model

Chung,

Parrenin,

Mulvaney

et al. 2024

Preprint

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Abstract. The European Beyond EPICA – Oldest Ice consortium is currently conducting an ice core drilling project at Little Dome C (LDC) in Antarctica with the aim of retrieving a continuous ice core up to 1.5 Ma. In order to determine the age of the ice at a given depth, 1D numerical models are often employed. However, they do not take into account any effects due to horizontal flow. We present a 2.5D inverse model that determines the age–depth profile along a flow line from Dome C (DC) to LDC that is assumed to be stable in time. The model is constrained by dated radar internal reflecting horizons. Surface velocity measurements are used to determine the flow line and ascertain the flow tube width, which also allows the model to consider lateral divergence. This new model therefore improves on the results produced by 1D models previously applied to the DC area. By inferring a mechanical ice thickness, the model predicts either the thickness of a basal layer of stagnant ice or a basal melt rate. Results show that the deepest ice at Beyond EPICA Little Dome C (BELDC) originates from around 15 km upstream. The oldest ice with useful age resolution, i.e. with an age density of 20 kyr m-1, is predicted to be 1.12 Ma at BELDC. Over the LDC area, the 2.5D model predicts a basal layer 200–250 m thick at the base of the ice sheet. Modelled ice particle trajectories suggest that this layer could be composed of stagnant ice, accreted ice or even disturbed ice containing debris. We explore the possibilities, though this is an open question that may only be answered by analysis the Beyond EPICA ice core once it has been drilled. Finally, we discuss in detail a thinning in the basal layer which is less than predicted by the model, as observed in other ice cores. This could mean that modelled ages are significantly over-estimated in the deepest part of the ice column. Given that the age estimate from the 2.5D model is younger than previous estimates, we suggest that horizontal flow is an important factor in this region. However, our model assumes that the flow line features such as flow direction and dome location have not change over the time period considered, which might not be the case.

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Section: Agementioning

confidence: 99%

Age, thinning and spatial origin of the Beyond EPICA ice from a 2.5D ice flow model

Chung,

Parrenin,

Mulvaney

et al. 2024

Preprint

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Mechanical Properties of Freshwater Ice

Baker,

Ogunmolasuyi

2024

J. Phys. Chem. C

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Freshwater ice, a crucial material in the context of climate change, exhibits unique mechanical behavior that is influenced by temperature, pressure, grain size, fabric, and impurity content. Understanding the mechanical behavior of freshwater ice is of critical importance in Earth Sciences, as ice cores are natural archives of the Earth's climate history, and in engineering as structures are built in cold regions. This work provides a comprehensive review of the mechanical properties of freshwater ice, with an emphasis on its strength, ductility, creep, and fracture behavior under various terrestrial conditions. A brief introduction to the different crystalline forms of ice, as well as the crystal structure and defects of ice Ih, is given. The effects of strain rate, temperature, grain size, confining pressure, impurities, and fabrics on the constant strain rate and constant load deformation behavior are explained. Additionally, methods for large-scale ice flow modeling and key results from such models are discussed. Finally, unresolved questions and directions for future research are presented.

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A Spectral Directors Method for Modeling the Coupled Evolution of Flow and CPO in Polycrystalline Olivine

Rathmann,

Mosegaard,

Bekkevold

et al. 2024

Geochem Geophys Geosyst

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The crystallographic preferred orientation (CPO) of polycrystalline olivine affects both the viscous and seismic anisotropy of Earth's upper mantle with wide geodynamical implications. In this methods paper, we present a continuous field formulation of the popular directors method for modeling the strain‐induced evolution of olivine CPOs, assuming the activation of a single preferred crystal slip system. The formulation reduces the problem of CPO evolution to a linear matrix problem that can easily be integrated alongside large‐scale geodynamical flow models, and conveniently minimizes the degrees of freedom necessary to represent CPO fields. We validate the CPO model against existing deformation experiments and naturally deformed samples, as well as the popular discrete grain model D‐Rex. A numerical model of viscoplastic thermal convection is built to illustrate how flow and CPO evolution may be two‐way coupled, suggesting that CPO‐induced viscous anisotropy does not necessarily strongly affect convection time scales, boundary (lid) stresses, and seismic anisotropy, compared to isotropic viscoplastic rheologies. As a consequence, geodynamical modeling that relies on an isotropic rheology (one‐way coupling) might suffice for predicting seismic anisotropy under some circumstances. Finally, we discuss limitations and shortcomings of our method, such as representing D‐ and E‐type fabrics or modeling flows with mixed fabric types, and potential improvements such as accounting for the effect of dynamic recrystallization.

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Simulating higher-order fabric structure in a coupled, anisotropic ice-flow model: application to Dome C

Cited by 4 publications

References 94 publications

Age, thinning and spatial origin of the Beyond EPICA ice from a 2.5D ice flow model

Age, thinning and spatial origin of the Beyond EPICA ice from a 2.5D ice flow model

Mechanical Properties of Freshwater Ice

A Spectral Directors Method for Modeling the Coupled Evolution of Flow and CPO in Polycrystalline Olivine

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