Ice stream subglacial access for ice-sheet history and fast ice flow: the BEAMISH Project on Rutford Ice Stream, West Antarctica and initial results on basal conditions

Three holes were drilled to the bed of Rutford Ice Stream, through ice up to 2154 m thick, to investigate the basal processes and conditions associated with fast ice flow and the glacial history of the West Antarctic Ice Sheet. A narrative of the drilling, measuring and sampling activities, as well as some preliminary results and initial interpretations of subglacial conditions, is given. These were the deepest subglacial access holes ever drilled using the hot-water drilling method. Samples of bed and englacial sediments were recovered, and a number of instruments were installed in the ice column and the bed. The ice-bed interface was found to be unfrozen, with an existing, well-developed subglacial hydrological system at high pressure, within ∼1% of the ice overburden. The bed itself comprises soft, water-saturated sediments, consistent with previous geophysical interpretations. Englacial sediment quantity varies significantly between two locations ∼2 km apart, and possibly over even shorter (∼20 m) distances. Difficulties and unusual observations encountered while connecting to the subglacial hydrological system in one hole possibly resulted from the presence of a large clast embedded in the bottom of the ice.