A new approach to inferring basal drag and ice rheology in ice streams, with applications to West Antarctic Ice Streams

Ranganathan, Meghana, Minchew, Brent, Meyer, Colin R. and Gudmundsson, Hilmar (2021) A new approach to inferring basal drag and ice rheology in ice streams, with applications to West Antarctic Ice Streams. Jourrnal of Glaciology, 67 (262). pp. 229-242. ISSN 0022-1430

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Official URL: https://doi.org/10.1017/jog.2020.95

Abstract

Drag at the bed and along the lateral margins are the primary forces resisting flow in outlet glaciers. Simultaneously inferring these parameters is challenging since basal drag and ice viscosity are coupled in the momentum balance, which governs ice flow. We test the ability of adjoint-based inverse methods to infer the slipperiness coefficient in a power-law sliding law and the flow-rate parameter in the constitutive relation for ice using a regularization scheme that includes coefficients weighted by surface strain rates. Using synthetic data with spatial variations in basal drag and ice rheology comparable to those in West Antarctic Ice Streams, we show that this approach allows for more accurate inferences. We apply this method to Bindschadler and MacAyeal Ice Streams in West Antarctica. Our results show relatively soft ice in the shear margins and spatially varying basal drag, with an increase in drag with distance upstream of the grounding line punctuated by localized areas of relatively high drag. We interpret soft ice to reflect a combination of heating through viscous dissipation and changes in the crystalline structure. These results suggest that adjoint-based inverse methods can provide inferences of basal drag and ice rheology when regularization is informed by strain rates.

Item Type: Article
Additional Information: Funding information: M.I.R. was funded through the Callahan Dee Fellowship and the Sven Treitel Fellowship. No new data were produced for this study, and data used in this study are publicly available through their respective publications. The source code for the model Úa is publicly available on Zenodo with DOI 10.5281/zenodo.3706624. The code to run the inversions can also be found there. The code that generates the ice streams and defines the parameters for the inversions for the synthetic tests and Bindschadler and MacAyeal can be found at https://github.com/megr090/Inversion_BasalDragIceRheology. Supplementary material. To view supplementary material of this article, please visit https://doi.org/10.1017/jog.2020.95
Uncontrolled Keywords: Antarctic glaciology, glacier flow, ice dynamics, ice rheology, ice streams
Subjects: F700 Ocean Sciences
F800 Physical and Terrestrial Geographical and Environmental Sciences
F900 Others in Physical Sciences
Department: Faculties > Engineering and Environment > Geography and Environmental Sciences
Depositing User: Rachel Branson
Date Deposited: 07 Dec 2020 12:14
Last Modified: 27 Apr 2021 09:00
URI: http://nrl.northumbria.ac.uk/id/eprint/44930

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