Preprints
https://doi.org/10.5194/tc-2022-222
https://doi.org/10.5194/tc-2022-222
 
02 Dec 2022
02 Dec 2022
Status: this preprint is currently under review for the journal TC.

Towards modelling of corrugation ridges at ice-sheet grounding lines

Kelly A. Hogan1, Katarzyna L. P. Warburton2,3, Alastair G. C. Graham4, Jerome A. Neufeld5,2, Duncan R. Hewitt6, Julian A. Dowdeswell7, and Robert D. Larter1 Kelly A. Hogan et al.
  • 1British Antarctic Survey, Cambridge, UK
  • 2Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, UK
  • 3Thayer School of Engineering, Dartmouth College, Hanover, NH, USA
  • 4College of Marine Science, University of South Florida, St Petersburg, FL, USA
  • 5Department of Earth Sciences, University of Cambridge, Cambridge, UK
  • 6Department of Mathematics, University College London, London, UK
  • 7Scott Polar Research Institute, University of Cambridge, Cambridge, UK

Abstract. Improvements in the resolution of seafloor mapping techniques have revealed extremely regular, sub-meter scale ridge landforms produced by the tidal flexure of ice-shelf grounding lines as they retreated very rapidly (i.e., at rates of several kilometres per year). Guided by such novel seafloor observations from Thwaites Glacier, West Antarctica, we present three mathematical models for the formation of these corrugation ridges at a tidally migrating grounding line (that is retreating at a constant rate) where each ridge is formed by either constant till flux to the grounding line, till extrusion from the grounding line, or by the resuspension and transport of grains from the tidal cavity. We find that both till extrusion (squeezing out till like toothpaste as the ice sheet re-settles on the seafloor), and resuspension and transport of material from the grounding-zone bed can qualitatively reproduce regular, delicate ridges at a retreating grounding line as described from seafloor observations. By considering the known properties of subglacial sediments we agree with existing schematic models that the most likely mechanism for ridge formation is till extrusion at each low-tide position, essentially preserving an imprint of the ice-sheet grounding line as it retreated. However, when realistic (shallow) bedslopes are used in the simulations ridges start to overprint one another suggesting that, to preserve the regular ridges that have been observed, grounding line retreat rates (driven by dynamic thinning?) may be even higher than previously thought.

Kelly A. Hogan 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-2022-222', Anonymous Referee #1, 14 Dec 2022
  • RC2: 'Comment on tc-2022-222', Sarah Greenwood, 04 Jan 2023

Kelly A. Hogan et al.

Data sets

Gridded multibeam bathymetry data from 'The Bump' at Thwaites Glacier, collected by 'Ran' Kongsberg Hugin AUV (Kongsberg EM2040), on the RV Nathaniel B. Palmer during cruise NBP19-02 (2019) Graham, A. G. C., Wåhlin, A. K., Hogan, K. A., Nitsche, F. O., Heywood, K. J., Minzoni, R., Smith, J. A., Hillenbrand, C.-D., Simkins, L., Wellner, J. S., and R. D. Larter https://doi.org/10.6084/m9.figshare.20359920.v1

Kelly A. Hogan et al.

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Short summary
Delicate seafloor ridges – corrugation ridges – that form by tidal motion at Antarctic grounding lines record extremely fast retreat of ice streams in the past. Here we use a mathematical model, constrained by real-world observations from Thwaites Glacier, West Antarctica, to explore how corrugation ridges form. We identify “till extrusion”, whereby deformable sediment is squeezed out from under the ice like toothpaste as it settles down at each low-tide position, as the most likely process.