Journal cover Journal topic
The Cryosphere An interactive open-access journal of the European Geosciences Union
doi:10.5194/tc-2017-54
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
05 May 2017
Review status
This discussion paper is under review for the journal The Cryosphere (TC).
Implementing an empirical scalar tertiary anisotropic rheology (ESTAR) into large-scale ice sheet models
Felicity S. Graham1, Mathieu Morlighem2, Roland C. Warner3, and Adam Treverrow3 1Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 129, Hobart, Tasmania 7001, Australia
2Department of Earth System Science, University of California, Irvine, California, USA
3Antarctic Climate and Ecosystems Cooperative Research Centre, Private Bag 80, Hobart, Tasmania 7001, Australia
Abstract. The microstructural evolution that occurs in polycrystalline ice during deformation leads to the development of anisotropic rheological properties that are not adequately described by the most common, isotropic, ice flow relation used in large-scale ice sheet models – the Glen flow relation. We present a preliminary assessment of the implementation in the Ice Sheet System Model (ISSM) of a computationally-efficient, empirical, scalar, tertiary, anisotropic rheology (ESTAR). The effect of this anisotropic rheology on ice flow dynamics is investigated by comparing idealised simulations using ESTAR with those using the isotropic Glen flow relation, where the latter includes a flow enhancement factor. For an idealised embayed ice shelf, the Glen flow relation overestimates velocities by up to 17 % when using an enhancement factor equivalent to the maximum value prescribed by ESTAR. Importantly, no single Glen enhancement factor can accurately capture the spatial variations in flow over the ice shelf. For flow-line studies of idealised grounded flow over a bumpy topography or a sticky base – both scenarios dominated at depth by bed-parallel shear – the differences between simulated velocities using ESTAR and the Glen flow relation vary according to the value of the enhancement factor used to calibrate the Glen flow relation. These results demonstrate the importance of describing the anisotropic rheology of ice in a physically realistic manner, and have implications for simulations of ice sheet evolution used to reconstruct paleo-ice sheet extent and predict future ice sheet contributions to sea level.

Citation: Graham, F. S., Morlighem, M., Warner, R. C., and Treverrow, A.: Implementing an empirical scalar tertiary anisotropic rheology (ESTAR) into large-scale ice sheet models, The Cryosphere Discuss., doi:10.5194/tc-2017-54, in review, 2017.
Felicity S. Graham et al.
Felicity S. Graham et al.
Felicity S. Graham et al.

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Short summary
Ice sheet flow is anisotropic, depending on the nature of the stress applied. However, most large-scale ice sheet models rely on the Glen flow relation, which ignores anisotropic effects. We implement an anisotropic flow relation (ESTAR) in a large-scale ice sheet model. In simulations of an ice shelf, the Glen flow relation overestimates velocities by up to 17 % compared with ESTAR. Our results have implications for ice sheet model simulations of paleo-ice extent and sea level rise predictions.
Ice sheet flow is anisotropic, depending on the nature of the stress applied. However, most...
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