Marine ice-sheet stability is mostly controlled by the dynamics of thegrounding line, i.e. the junction between the grounded ice sheet and thefloating ice shelf. Grounding line migration has been investigated within theframework of MISMIP (Marine Ice Sheet Model Intercomparison Project), whichmainly aimed at investigating steady state solutions. Here we focus ontransient behaviour, executing short-term simulations (200 yr) of a steadyice sheet perturbed by the release of the buttressing restraint exerted bythe ice shelf on the grounded ice upstream. The transient grounding linebehaviour of four different flowline ice-sheet models has been compared. Themodels differ in the physics implemented (full Stokes and shallow shelfapproximation), the numerical approach, as well as the grounding linetreatment. Their overall response to the loss of buttressing is found to bebroadly consistent in terms of grounding line position, rate of surfaceelevation change and surface velocity. However, still small differencesappear for these latter variables, and they can lead to large discrepancies(> 100%) observed in terms of ice sheet contribution to sea level whencumulated over time. Despite the recent important improvements of marine ice-sheet models in their ability to compute steady state configurations, ourresults question the capacity of these models to compute short-term reliablesea-level rise projections.
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