Glaciated Margin

Ice sheets have advanced and retreated across the glaciated margins in a series of climate-related cycles. Research focus on regional morphology and sedimentary architecture of continental slopes (e.g. Laberg & Vorren, 1995; e.g. Dowdeswell et al., 1996) has shown that during glacial maxima, the ice sheets expanded across continental shelves to the shelf edge. However, the delivery of ice and sediments to the continental shelf edge is heterogeneous; a pattern of flow-partition into low and fast-flowing ice (ice streams) having been described (Sejrup et al., 2000). Ice streams are responsible for discharging the majority of the ice and sediment within ice sheets. Thousands of cubic kilometres of sediment were transported to the Norwegian shelf edge (e.g. Hjelstuen et al., 2004b) during the mid and late Pleistocene by ice streams. Ice streams also play a critical role in driving abrupt changes in high-latitude climate and oceanography.

This high sediment flux supplied enough material for the development and the build-up of the large glacier-fed fan systems on the continental slope of offshore of these fast-flowing ice streams. These fans have been termed Trough-Mouth Fans (TMFs) by Vorren and Laberg (1997), as they are located in front of depressions on the shelf, and were the main depocentres of glacigenic sediments on the Norwegian Margin during the Quaternary (King et al., 1996; Dowdeswell et al., 1998; Taylor et al., 2002). It has been estimated that 15-20% of the Late Weichselian sediment input to the deep-basins was by the North Sea Fan and the Bear Island Fan, contributing approximately 1000 km3 each (Taylor et al., 2002). However, the flux of sediment delivered to the deep-basins through the fan is only high during glacial maxima when ice sheets are located at or near the shelf break.

Last Glacial Maximum (28-22 ka) extent of the Fennoscandian, UK, and western Barents ice sheets, with distribution of glacial fed fans on the margins and possible location of former ice streams indicated. BIF – Bear Island Fan; NSF – North Sea Fan(Sejrup et al., 2000).

The topography/morphology of the glaciated margins is only slightly modified during the deglaciation of the shelf. However, even during the interglacials the glaciated margins retain a glacimarine overprint since ice sheets terminating in marine waters still deliver icebergs, meltwater and debris. Apart from a few slides, the sea-floor remained largely unchanged during the Holocene, only modified by current activity and deposition of a very thin drape of sediments (<10 centimetres on average), iceberg reworking of the shallow areas, contourite drifts, and the formation of pockmarks and other gas-escape structures.

Although shaped by the same main processes, glaciated margins can also be quite distinct. That can be observed by comparing the Eastern North Atlantic, characterised by few large slope failures and large fans, with the Western North Atlantic, which accommodates abundant small failures (Huhnerbach & Masson, 2004).