01510nas a2200193   4500000000100000000000100001008004100002260002000043100001800063700001500081700001300096700001500109700001800124245006500142856005800207300001200265490000700277520103200284       2008                            d  cOctober 1, 20081 aJ. Dowdeswell1 aD. Ottesen1 aJ. Evans1 aC. Cofaigh1 aJ.B. Anderson00aSubmarine glacial landforms and rates of ice-stream collapse  uhttp://geology.gsapubs.org/content/36/10/819.abstract  a819-8220 v363 aThe rate of deglacial ice-sheet retreat across polar continental shelves, and possible ice-stream collapse and sea-level rise, has been much debated. High-resolution imagery of seafloor morphology is available for many polar shelves and fjords. The rapidity of ice retreat is inferred from diagnostic assemblages of submarine landforms, produced at ice-stream sedimentary beds. These landforms, exposed by ice retreat across high-latitude shelves, demonstrate that deglaciation occurs in three main ways: rapidly, by flotation and breakup; episodically, by still-stands and/or grounding events punctuating rapid retreat; or by slower retreat of grounded ice. Submarine landform assemblages imply, through the presence of grounding-zone wedges overprinting mega-scale glacial lineations on many polar shelves, that ice-stream retreat is more often episodic than catastrophic. These observations provide a robust test of the ability of numerical models to predict the varied response of ice-sheet basins to environmental changes.