EXCEPTIONS TO BED-CONTROLLED ICE SHEET FLOW AND RETREAT FROM GLACIATED CONTINENTAL MARGINS WORLDWIDE (Invited Presentation)

Projections of ice sheet behaviour hinge on how ice flow velocity evolves and the extent to which marine-based grounding lines are stable. Ice flow and grounding line retreat are variably governed by the coupling between the ice and underlying terrain. We ask to what degree catchment-scale bed characteristics determine ice flow and retreat, drawing on the landform imprint of palaeo-ice sheets from 99 sites on continental shelves around the world. We find that topographic setting has broadly steered ice flow, and that the bed slope favours particular styles of grounding line retreat. However, we find exceptions to accepted ‘rules’ of behaviour: regional topographic highs are not always an impediment to fast ice flow, retreat may proceed in a controlled, steady manner on reverse slopes and, surprisingly, substrate geology does not dictate ice flow or retreat style. Furthermore, once grounding line retreat is underway, readvance is rarely observed regardless of regional bed characteristics.