Sedimentation beneath ice shelves - the view from ice stream B

Ice-shelf development is favored by rapid flow of cold ice from outlet glaciers or ice streams into protected embayments with localized high spots. Basal melting of ice shelves is rapid near the ice front and may occur near the grounding line. Ice from outlet glaciers may contain significant englacial debris that is deposited as a dropstone diamicton in regions of basal melting. Englacial debris is sparse or absent in ice streams. Evidence from ice stream B, draining into the Ross Ice Shelf of West Antarctica, suggests that the rapid ice velocity arises from deformation of a several-meter-thick, water-saturated basal till layer that is eroding an unconformity on sediments beneath and that has deposited a "till delta" tens of meters thick and tens of kilometers long at the grounding line. Sea-level fall would cause "conveyor belt" recycling of this till delta and grounding-line advance across the Ross Sea to the edge of the continental shelf, forming an ice sheet with a low, ice-stream profile resting on a several meter-thick deforming till layer eroding an unconformity. The modern Ross Sea is characterized by a regional unconformity overlain by a diamicton of probable latest Pliocene-Pleistocene age measuring several meters to tens of meters thick. We hypothesize that this diamicton is a deformed glacial till and that the Ross Sea sediments record one or more expansions of the till-lubricated West Antarctic ice sheet to the edge of the continental shelf.