Ice-sheet dynamics and ice streaming along the coastal parts of northern Norway

Abstract

In this paper, regional and high-resolution bathymetric data are used to reconstruct the pattern and dynamics of ice-sheet flow in the fjord and shelf areas of northern Norway. Interpretation of the morphology of the sea floor reveals a series of glacigenic features, which are mainly related to the most recent glaciation of the area. The shelf area of Troms county comprises four cross-shelf troughs with intermediate shallow banks. Glacial features within the cross-shelf troughs (mega-scale glacial lineations (MSGL), lateral shear margin moraines, grounding zone wedges) are interpreted to have been formed under fast-flowing ice streams. On the shallow bank areas, there are far fewer ice-flow indicators and here, relatively passive ice acted as interstream ridges. Outside the Finnmark coast, to the north and east, a coast-parallel depression (Djuprenna) deflected rapidly flowing ice from the fjords in a generally east to west direction, and then farther out through Ingøydjupet and into the Bear Island Trough. The fjords guided most of the ice flow and functioned as tributaries to the major ice streams on the shelf, including the vast Bear Island Trough Ice Stream at the Last Glacial Maximum. The landform distribution and their cross-cutting relationships indicate that major switches in ice-stream flow direction took place during deglaciation. Additionally, grounding zone wedges are found within the cross-shelf troughs and these reveal temporal variability in ice-stream dynamics in different troughs during deglaciation. The distribution of glacigenic features on the ice-stream beds also reveals a downstream evolution that has been reported by other workers, whereby small bedrock features progressively merge into more elongate forms and MSGL. This downstream evolution in subglacial geology/subglacial bedforms implies that the force balance (e.g. basal shear stress) of the ice streams also evolves in the downstream direction and, more crucially, that the flow mechanism of the ice stream is spatially variable along its length.