Towards modelling of corrugation ridges at ice-sheet grounding lines

Improvements in the resolution of sea-floor mappingtechniques have revealed extremely regular, sub-metre-scale ridge landformsproduced by the tidal flexure of ice-shelf grounding lines as they retreatedvery rapidly (i.e. at rates of several kilometres per year). Guided by suchnovel sea-floor observations from Thwaites Glacier, West Antarctica, wepresent three mathematical models for the formation of these corrugationridges at a tidally migrating grounding line (that is retreating at aconstant rate), where each ridge is formed by either constant till flux tothe grounding line, till extrusion from the grounding line, or theresuspension and transport of grains from the grounding-zone bed. We findthat both till extrusion (squeezing out till like toothpaste as the icesheet re-settles on the sea floor) and resuspension and transport ofmaterial can qualitatively reproduce regular, delicate ridges at aretreating grounding line, as described by sea-floor observations. Byconsidering the known properties of subglacial sediments, we agree withexisting schematic models that the most likely mechanism for ridge formationis till extrusion at each low-tide position, essentially preserving animprint of the ice-sheet grounding line as it retreated. However, whenrealistic (shallow) bed slopes are used in the simulations, ridges start tooverprint one another, suggesting that, to preserve the regular ridges thathave been observed, grounding line retreat rates (driven by dynamicthinning?) may be even higher than previously thought.