Possible ‘lift-off moraines’ at grounded ice-sheet margins, North Norwegian shelf edge

Abstract

Small but regular variations in ice-sheet horizontal velocity have been linked to buoyancy-related tidal forcing beneath modern Antarctic ice streams (e.g. Bindschadler et al. 2003; Gudmundsson 2006). Given this sensitivity to tidal amplitudes of only a metre or two, it is likely that grounding zones at the tidewater margins of Quaternary ice sheets were also affected by buoyancy changes linked to tides. Ottesen & Dowdeswell (2009) observed a linear belt of irregular hummocky seafloor terrain at the full-glacial margin of a grounded Late Quaternary ice sheet at the NW Spitsbergen shelf edge. They proposed that this distinctive morphology might be linked to buoyancy fluctuations at this former grounding zone. We describe and interpret extensive belts of similar hummocky terrain from the margins of a full-glacial ice sheet at the North Norwegian shelf edge. Between 68° 50′ N and 69° 25′ N, the Norwegian continental shelf narrows to about 30 km off Vesteralen archipelago. This area comprises shallow banks (40–120 m deep) and is understood to have been located between fast-flowing ice streams in the Late Weichselian Ice Sheet; it is therefore likely to have experienced limited ice flow. Within 6 km of the shelf edge, belts of hummocky, undulating ridges are found both on banks (Fig. 1) and in shallower parts of adjacent troughs. The ridges occur at water-depths of 85–160 m, and …