Devensian Ice-Sheet history of the western North Sea

Abstract

The ice masses of present-day Greenland and Antarctica are characterised by marine-terminating
ice streams and outlet glaciers, which deliver the majority of ice to the surrounding
ocean and have a large impact on the ice sheet stability and sea-level. Understanding the
break-up of palaeo-ice sheets and ice streams is thus considered crucial for understanding
contemporary ice sheet behaviour and ice sheet response to global climate change.
The history of the former eastern margin of the last British and Irish Ice Sheet (BIIS)
is still poorly understood, particularly in the western North Sea. The BIIS is known to have
overrun the eastern coasts of England and Scotland at different times during the Pleistocene
and to have extended offshore. It was drained by numerous ice streams, which experienced
different phases of activity during the Last Glacial Maximum (LGM). However, despite recent
improvements in the understanding of the onshore glacial history of the region, still little is
known about the offshore sector. In particular, significant gaps remain in the knowledge of the
deglacial history of the BIIS from the western North Sea, and of the dynamic behaviour of the
North Sea Lobe (NSL) ice stream as it retreated from the offshore region.
This research incorporates different bathymetric, seismic and sedimentological datasets
collected in the western North Sea, to investigate the geomorphological and sedimentary
imprint left on the seafloor by the passage of the BIIS and by the NSL during the last
glacial phase. The findings provide new insights on the seafloor geomorphology and on the
stratigraphic architecture of the Quaternary sediments of the area, and better reconstruct the
advance and retreat behaviour of the NSL in the region. The results demonstrate that the
geomorphological imprint found on the seafloor of the western North Sea can be ascribable
to the action of the NSL, which was flowing from NW to SE. The presence of Grounding
Zone Wedges and of glaciomarine sediments characterised by cold temperature foraminifera
species, known to be indicators of extreme glacial marine environments, indicates that the NSL
was a marine-terminating ice lobe in the investigated area during retreat and that its decay was
episodic, punctuated by phases of temporary stability. Bedrock strata, which is present at or
very close to the seabed, is thought to have provided pinning points that facilitated periods of
ice stillstand. In addition, new radiocarbon ages constrain ice retreat towards southern Scotland
between ~19 - 16 ka BP, and suggest that deglaciation of this sector of the North Sea started
earlier than previously thought.