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Abstract

Ice sheets fundamentally contribute to the climate system by exchanging freshwater with the oceans and influencing the Earth's radiative balance via their surface albedo. On the other hand, changing climatic conditions (precipitation, air and ocean temperature) as well as geothermal heat fluxes control the advance and retreat of ice sheets during glacial cycles. With the changing ice and ocean load on the Earth's surface, their evolution forces the redistribution of mantle material in the Earth's interior and causes changes of the gravity field and the displacement of the surface, both leading to sea-level change. The gravitational and deformational response depends on the viscoelastic structure of the solid Earth, which in turn has an effect on the dynamic evolution of the ice sheets. In this thesis, a coupled model for ice and solid-Earth dynamics is realized, consistently accounting for surface loading of the Earth by redistribution of ice and ocean masses. It incorporates all primary feedbacks of viscoelastic deformation and gravitationally consistent sea level on the evolution of the modeled ice sheets. In idealized scenarios, it is found that the feedback mechanisms are most important at the boundary between grounded ice and oceans. This feedback is shown to be not adequately accounted for in an approximative representation of the solid-Earth deformation, commonly used in ice-sheet modeling. A possible future collapse of the West Antarctic Ice Sheet (WAIS) in a warming climate including rising sea levels is found to be prevented or delayed by soft viscoelastic Earth structures (i.e. featuring a thin lithosphere and a low-viscous asthenosphere), corresponding to the West Antarctic rift system. It is found that the iterative adjustment of the paleo bathymetry, necessary to match present-day observation of the bathymetry, as well as the ongoing relaxation imply shallower ambient ocean depths in Antarctica for stiffer Earth structures (i.e. featuring a thick lithosphere and a high-viscous mantle) during the last glacial cycle, leading to more stability during intermittent periods of warming preceding the Last Glacial Maximum (LGM). The findings on the future WAIS stability for softer Earth structures and the additional pre-LGM stability of the Antarctic Ice Sheet for stiffer Earth structures largely depend on the strength of the applied forcing of the ice dynamics. If, however, the ice sheet is forced to a tipping point, the solid-Earth structure may turn the balance towards stabilization or considerable ice-mass loss and associated sea-level rise. Therefore, the simultaneous consideration of ice dynamics and the Earth's deformational and gravitational response as in the presented coupled model provides a more reliable insight into ice dynamics.