Ice-core evidence of the thickness and character of clear-facies basal ice: Glacier de Tsanfleuron, Switzerland

Five ice cores have been retrieved from a transect close to the terminus of Glacier de Tyanfleuron. Switzerland. The cores extend from the ice surface to the glacier bed, and are 3.5-44.8 m long. Stratigraphic logging based o n bubble size and density reveals the presence of a highly metamorphosed ba sal ice layer, about 10 m thick, from which all traces of bubble-rich ice h ave been removed. This bubble-poor ice, which corresponds closely with clea r-facies ice observed in cavities beneath numerous temperate-based glaciers , contrasts with the overlying bubble-rich or bubble-foliated englacial ice and the underlying debris-rich and bubble-free dispersed-facies basal ice. Down-core patterns in major-ion composition. stable-isotope composition and total gas content and composition are generally consistent with formation of clear-facies ice by deformation-related metamorphism or bubbly, englacia l ice. In addition, isotopic data suggest that storage of downward-percolat ing meltwaters occurs close to the upper surface of the clear-facies ice la yer, perhaps reflecting a local variation in ice permeability across the tr ansition from englacial to clear-facies ice. Enrichment in crustally derive d ionic species is noted in the lowermost decimetres of the debris-free. cl ear-facies ice that immediately overlies debris-rich dispersed-facies basal ice. This ionic enrichment in debris-free ice is interpreted in terms of a ctive inter-granular meltwater flow within some decimeters of the glacier b ed.