| Summary: | In many ice streams, basal resistance varies in space and time due to the dynamically evolving properties of subglacial till. These variations can cause internally generated oscillations in ice-stream flow. However, the potential for such variations in basal properties is not considered by conventional theories of grounding-line stability on retrograde bed slopes, which assume that bed properties are static in time. Using a flow-line model, we show how internally generated, transient variations in ice-stream state interact with retrograde bed slopes. In contrast to predictions from the theory of the marine ice-sheet instability, our simulated grounding line is able to persist and reverse direction of migration on a retrograde bed when undergoing oscillations in the grounding-line position. In turn, the presence of a retrograde bed may also suppress or reduce the amplitude of internal oscillations in ice-stream state. We explore the physical mechanisms responsible for these behaviors and discuss the implications for observed grounding-line migration in West Antarctica. © 2016 Author(s). CC Attribution 3.0 License. Published by Copernicus Publications on behalf of the European Geosciences Union. Received: 22 January 2016 – Published in The Cryosphere Discuss.: 14 March 2016. Revised: 8 August 2016 – Accepted: 9 August 2016 – Published: 25 August 2016. This work has been supported by the NSF grant AGS-1303604 (Alexander A. Robel and Eli Tziperman). Eli Tziperman thanks the Weizmann Institute for its hospitality during parts of this work. Alexander A. Robel has been supported by the NSF Graduate Research Fellowship. Christian Schoof has been supported by NSERC Discovery Grant no. 357193-12. Published - CytosRobel,AAetal.pdf
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