Characteristics of basal ice at Engabreen, northern Norway

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Abstract
Subglacial intakes in a tunnel system underneath Engabreen, northern Norway, provide access to the underside of a 200 m thick glacier. Detailed observations and measurements were made in several ice tunnels melted out along the glacier bed. A 20–200 cm thick basal sediment layer is overlain by clean glacier ice. Stratigraphy is complex, with alternating sediment-rich and sediment-free layers, and pervasive shearing. Throughout the basal ice are numerous spheroidal water pockets, which increase in both size and degree of elongation with distance from the bed. Ice cores were retrieved from ice-tunnel walls for sediment, cation and isotope analysis. Our observations and measurements provide evidence for both accretion in and water movement through the basal ice. This supports the modification to classical regelation theory proposed recently by Lliboutry in which water flow in the vein network is required to achieve net accretion of regelation layers.