Retreat history of the last glacial maximum ice sheet in Ross Sea, Antarctica
Shipp, Stephanie Staples
Anderson, John B.
Doctor of Philosophy
High-resolution geophysical and geologic data were acquired in western and central Ross Sea, Antarctica, to determine the: (1) maximum extent and configuration of the ice sheet during the Last Glacial Maximum (LGM); (2) conditions and processes at the base of the expanded ice sheet and their role in ice stream activity; and (3) relative retreat history of the ice sheet. This information can provide geologic constraints for modeling of ice-sheet retreat. The research formed the basis for development of a public Web site (http://www.glacier.rice.edu) and for middle-school earth-science instructional materials. Based on identification of isolated grounding-zone wedges and consistency of mega-scale glacial lineations, the LGM ice edge reached the Coulman Island region in western Ross Sea. The maximum extent in central Ross Sea occurred at the continental-shelf edge, based on the presence of mega-scale glacial lineations, glacio-tectonic features, and shelf-edge gullies. Streaming ice, overlying a deforming bed typically <5 m in thickness, filled the troughs. Thinner, divergent, slower moving ice, not underlain by deforming sediment, occupied the bank tops. The ice sheet eroded and conveyed sediment from the inner regions toward the outer shelf, where the material was deposited at the grounding line. No features associated with meltwater occur; water available to the subglacial system probably was incorporated into a deforming unit. The ice sheet may have undergone an initial phase of mass wasting, based the large, arcuate iceberg furrows associated with the grounding zones. Ice retreated first from western Ross Sea, possibly because of a diminished contribution from the East Antarctic Ice Sheet. Ice retreat from central Ross Sea lagged that of western Ross Sea. The banks remained ice covered after ice retreat from the troughs; ice shelves may have covered the troughs. During retreat, the grounded ice reworked the substrate into back-stepping grounding-zone wedges and corrugation moraines. The latter features exhibit a spacing on the order of 40 to 100 m and may record annual retreat. This argues for gradual retreat and negates catastrophic collapse of the ice sheet.