Abstract The bedrock beneath the Antarctic Ice Sheet has experienced widespread viscoelastic deformation as a response to ice-sheet changes from the Last Glacial Maximum (LGM) to present day. The combined changes of the ice sheet and the bedrock most likely had impacted subglacial water routes. Using the evolution of bedrock elevation simulated with two coupled ice-sheet and glacial isostatic adjustment (GIA) models, we explore changes to the subglacial water routes from the LGM to the present day. We explore the sensitivity of our results to bed roughness by repeating the calculations using 10 topographic realizations, and estimate the relative impacts of changes in the bedrock elevation and the ice surface slope. Our results show that bedrock elevation changes of up to ∼400 m likely led to a large enough change in tilt of the bedrock, such that subglacial water routing during the last deglacial phase likely differed significantly from patterns inferred at present day. The impact of GIA on subglacial flow paths is thus non-negligible and should be accounted for in reconstructions of ancient subglacial hydrology and studies of past sediment provenance.

Rifts are full-thickness fractures that propagate laterally across an ice shelf. They cause ice-shelf weakening and calving of tabular icebergs, and control the initial size of calved icebergs. Here, we present a joint inverse and forward computational modeling framework to capture rifting by combining the vertically integrated momentum balance and anisotropic continuum damage mechanics formulations. We incorporate rift–flank boundary processes to investigate how the rift path is influenced by the pressure on rift–flank walls from seawater, contact between flanks, and ice mélange that may also transmit stress between flanks. To illustrate the viability of the framework, we simulate the final 2 years of rift propagation associated with the calving of tabular iceberg A68 in 2017. We find that the rift path can change with varying ice mélange conditions and the extent of contact between rift flanks. Combinations of parameters associated with slower rift widening rates yield simulated rift paths that best match observations. Our modeling framework lays the foundation for robust simulation of rifting and tabular calving processes, which can enable future studies on ice-sheet–climate interactions, and the effects of ice-shelf buttressing on land ice flow.

Investigations of the time-dependent behavior of marine ice sheets and their sensitivity to basal conditions require numerical models because existing theoretical analyses focus only on steady-state configurations primarily with a power-law basal shear stress. Numerical results indicate that the choice of the sliding law strongly affects ice-sheet dynamic behavior. Although observed or simulated grounding-line retreat is typically interpreted as an indication of marine ice sheet instability introduced by Weertman (1974), this (in)stability is a characteristic of the ice sheet s steady states –not time-variant behavior. To bridge the gap between theoretical and numerical results, we develop a framework to investigate grounding line dynamics with generalized basal and lateral stresses (i.e. the functional dependencies are not specified). Motivated by observations of internal variability of the Southern Ocean conditions we explore the grounding-line response to stochastic variability. We find that adding stochastic variability to submarine melt rates that produced stable steady-state configurations leads to intermittently advancing and retreating grounding lines. They can also retreat in an unstoppable manner on time-scales significantly longer than the stochastic correlation time-scales. These results suggest that at any given time of their evolution, the transient behavior of marine ice sheets cannot be described in terms of stable or unstable .