20 Sep 2021
20 Sep 2021
Status: a revised version of this preprint is currently under review for the journal TC.

Inverting ice surface elevation and velocity for bed topography and slipperiness beneath Thwaites Glacier

Helen Ockenden, Robert G. Bingham, Andrew Curtis, and Daniel Goldberg Helen Ockenden et al.
  • School of GeoSciences, University of Edinburgh, Drummond St, Edinburgh EH8 9XP, UK

Abstract. There is significant uncertainty over how ice sheets and glaciers will respond to rising global temperatures. Limited knowledge of the topography and rheology of ice-bed interface is a key cause of this uncertainty, as models show that small changes in the bed can have a large influence on predicted rates of ice loss. Most of our detailed knowledge of bed topography comes from airborne and ground-penetrating radar observations. However, these direct observations are not spaced closely enough to meet the requirements of ice-sheet models, so interpolation and inversion methods are used to fill in the gaps. Here we present the results of a new inversion of surface-elevation and velocity data over Thwaites Glacier, West Antarctica, for bed topography and slipperiness (i.e. the degree of basal slip for a given level of drag). The inversion is based on a steady-state linear perturbation analysis of the shallow-ice-stream equations. The method works by identifying disturbances to surface flow which are caused by obstacles or sticky patches in the bed, and can therefore be applied wherever the shallow-ice-stream equations hold and where surface data are available, even where the ice thickness is not well known. We assess the performance of the inversion for topography with the available radar data. Although the topographic output from the inversion is less successful where the bed slopes steeply, it compares well with radar data from the central trunk of the glacier. This method could therefore be useful as either an independent test of other interpolation methods such as mass conservation and kriging, or as a complementary technique in regions where those techniques fail. We do not have data to allow us to assess the success of the slipperiness results from our inversions, but we provide maps that may guide future seismic data collection across Thwaites Glacier. The methods presented here show significant promise for using high-resolution satellite datasets, calibrated by the sparser field datasets, to generate high resolution bed topography products across the ice sheets, and therefore contribute to reduced uncertainty in predictions of future sea-level rise.

Helen Ockenden et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2021-287', Anonymous Referee #1, 29 Nov 2021
    • AC1: 'Reply on RC1', Helen Ockenden, 23 Mar 2022
  • RC2: 'Comment on tc-2021-287', Anonymous Referee #2, 05 Jan 2022
    • AC2: 'Reply on RC2', Helen Ockenden, 23 Mar 2022

Helen Ockenden et al.

Helen Ockenden et al.


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Short summary
Hills and valleys hidden under the ice of Thwaites Glacier have an impact on ice flow and future ice loss, but there are not many three dimensional observations of their location or size. We apply a mathematical theory to new high resolution observations of the ice surface to predict the bed topography beneath the ice. There is a good correlation with ice-penetrating radar observations. The method may be useful in areas with few direct observations, or as a further constraint for other methods.