25 Apr 2022
25 Apr 2022
Status: this preprint is open for discussion.

Hysteretic evolution of ice rises and ice rumples in response to variations in sea level

A. Clara J. Henry1,2,3, Reinhard Drews2, Clemens Schannwell1, and Vjeran Višnjević2 A. Clara J. Henry et al.
  • 1Max Planck Institute for Meteorology, Bundesstr. 53, 20146 Hamburg, Germany
  • 2Department of Geosciences, University of Tübingen, Schnarrenbergstr. 94-96, 72076 Tübingen, Germany
  • 3International Max Planck Research School on Earth System Modelling, Max Planck Institute for Meteorology, Hamburg, Germany

Abstract. Ice rises and ice rumples are locally grounded features found in coastal Antarctica and are surrounded by otherwise freely floating ice shelves. An ice rise has an independent flow regime, whereas the flow regime of an ice rumple conforms to that of the ice shelf and merely slows the flow of ice. In both cases, local highs in the bathymetry are in contact with the ice shelf from below, thereby regulating the large-scale ice flow, with implications for the upstream continental grounding line position. This buttressing effect, paired with the suitability of ice rises as a climate archive, necessitates a better understanding of the transition between ice rise and ice rumple, their evolution in response to a change in sea level, and their dynamic interaction with the surrounding ice shelf. We investigate this behaviour using a three-dimensional full Stokes ice flow model. The simulations span end-member basal friction scenarios of almost stagnant and fully sliding ice at the ice-bed interface. We analyse the coupling with the surrounding ice shelf by comparing the deviations between the non-local full Stokes surface velocities and the local shallow ice approximation (SIA). Deviations are generally high at the ice divides and small on the lee sides. On the stoss side, where ice rise and ice shelf have opposing flow directions, deviations can be significant. Differences are negligible in the absence of basal sliding where the corresponding steady state ice rise is larger and develops a fully independent flow regime that is well described by SIA. When sea level is increased and a transition from ice rise to ice rumple is approached, the divide migration is more abrupt the higher the basal friction. In each scenario, the transition occurs after the stoss side grounding line has moved over the bed high and is positioned on a retrograde slope. We identify a hysteretic response of ice rises and ice rumples to changes in sea level, with grounded area being larger in a sea level increase scenario than in a sea level decrease scenario. This hysteresis not only shows irreversibility following an equal increase and subsequent decrease in sea level, but also has important implications for ice flow model initialisation. The initial grounded area needs to be carefully considered, as this will determine the formation of either an ice rise or an ice rumple, thereby causing different buttressing effects.

A. Clara J. Henry et al.

Status: open (until 20 Jun 2022)

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A. Clara J. Henry et al.

A. Clara J. Henry et al.


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Short summary
We used a 3D, idealised model to study features in coastal Antarctica called ice rises and ice rumples. These features regulate the rate of ice flow into the ocean. We show that when sea level is raised or lowered, the size of these features and the ice flow pattern can change. We find that the features depend on the ice history and do not necessarily fully recover after an equal increase and decrease of sea level. This shows that it is important to initialise models with accurate ice geometry.