A document by Alan R.A. Aitken. Click on the document to view its contents.

Ice rises situated around the perimeter of Antarctica buttress ice flow and contain information about the past climate and changes in flow regime. Moreover, ice rises contain convergent and divergent flow regimes, and both floating and grounded ice over comparatively small spatial scales, meaning they are ideal locations to study ice-flow dynamics. Here, we introduce a new modelling framework that permits the comparison between modelled and observed stratigraphy. A thermo-mechanically coupled, isotropic, full Stokes ice flow model with a dynamic grounding line is used (Elmer/Ice). The result is the simulated age-depth field of a three-dimensional, steady-state ice rise which is dynamically coupled to the surrounding ice shelf. Applying the model to Derwael Ice Rise, results show a good match between observed and modelled stratigraphy over most of the ice rise and predict approximately $8000$ year old ice at a depth of $95$ \%. Differences in the prediction of age between simulations using Glen’s flow law exponents of $n=3$ and $n=4$ are generally small ($<5$ \% over most areas). In the ice rise shear zones, large differences in shear strain rates in the velocity direction are found between the $n=3$ and the $n=4$ simulations. Our simulations indicate that a Glen’s flow law exponent of $n=4$ may be better suited when modelling ice rises due to a steady-state geometry which is closer to the observed geometry. Our three-dimensional modelling framework can easily be transferred to other ice rises and has relevance for researchers interested in ice core dating and understanding ice-flow re-organisation.

A document by Hameed Moqadam. Click on the document to view its contents.

The shape of ice-shelf cavities are a major source of uncertainty in understanding ice-ocean interactions. This limits assessments of the response of the Antarctic ice sheets to climate change. Here we use vibroseis seismic reflection surveys to map the bathymetry beneath the Ekström Ice Shelf, Dronning Maud Land. The new bathymetry reveals an inland-sloping trough, reaching depths of 1100 m below sea level, near the current grounding line, which we attribute to erosion by palaeo-ice streams. The trough does not cross-cut the outer parts of the continental shelf. Conductivity-temperature-depth profiles within the ice-shelf cavity reveal the presence of cold water at shallower depths and tidal mixing at the ice-shelf margins. It is unknown if warm water can access the trough. The new bathymetry is thought to be representative of many ice shelves in Dronning Maud Land, which together regulate the ice loss from a substantial area of East Antarctica.

Improving constraints on the basal ice/bed properties is essential for accurate prediction of ice-sheet grounding-line positions and stability. Furthermore, the history of grounding-line positions since the Last Glacial Maximum has proven challenging to understand due to uncertainties in bed conditions. Here we use a 3D full-Stokes ice-sheet model to investigate the effect of differing ocean bed properties on ice-sheet advance and retreat over a glacial cycle. We do this for the Ekström Ice Shelf catchment, East Antarctica. We find that predicted ice volumes differ by >50%, resulting in two entirely different catchment geometries triggered exclusively by variable ocean bed properties. Grounding-line positions between simulations differ by >100% (49 km), show significant hysteresis, and migrate non-steadily with long quiescent phases disrupted by leaps of rapid migration. These results highlight that constraints for both bathymetry and substrate geologic properties are urgently needed for predicting ice-sheet evolution and sea-level change.