The basal regime of the West-Antarctic ice sheet interaction of subglacial geology with ice dynamics

Covered by up to 4 km of ice, the basal zone of the West-Antarctic Ice Sheet is one of the most inaccessible and unknown environments on Earth. Yet basal conditions play a key role in facilitating fast ice streaming and influence the mass balance of the ice sheet by controlling the rate of ice discharge.; Fast ice streaming is possible where subglacial sediment and basal water is available. Mixed with basal water subglacial sediment provides little resistance against the flow of ice. Basal melting at the base of the ice sheet is dependent on the basal energy balance, determined by the geothermal flux, basal shear heating and the conductive heat escape through the ice.; Recent advances in remote sensing allowed the acquisition of spatial data sets necessary to model the basal melt distribution beneath the ice sheet. Results of numerical models indicate that basal melting occurs where geothermal heat is trapped beneath up to 4 km thick ice in the WAIS interior or frictional heating exceeds the heat escape through the thinner ice of fast flowing ice streams. In ice stream tributaries, which feed ice from the WAIS interior towards the ice streams, basal freeze-on may allow the formation of several meters thick, accretionary basal ice layer.; Borehole videos from the base of Kamb Ice Stream reveal a 10--14 m thick layer of sediment-laden basal ice and a 1.6 m deep water-filled cavity. Representing a several thousand-year record of basal freezing, its presence suggests that the shutdown of Kamb Ice Stream was associated with basal freeze-on and limited availability of basal water. The build-up of basal water over the last several decades suggests that the mechanism for shutdown has disappeared. Re-lubrication of the ice base may reactivate Kamb Ice Stream leading to a significant increase in the contribution of West-Antarctica to the global sea level.; Active or recently active subglacial volcanism may play an important role in the production of subglacial water. Based on the interpretation of magnetic anomaly maps existence of large amounts of late Cenozoic subglacial flood basalts had been proposed. Petrological and geochemical characterization of subglacial sediment and sediment derived from basal-ice (basal sediment) however indicates that mafic volcanics, if responsible for these anomalies, are considerably older than Late Cenozoic (Mesozoic or Paleozoic), reducing the likelihood of considerable contribution to the geothermal flux significantly.