The northern sector of the last British Ice Sheet: Maximum extent and demise

Abstract

Strongly divided opinion has led to competing, apparently contradictory, views on the timing, extent, flow configuration and decay mechanism of the last British Ice Sheet. We review the existing literature and reconcile some of these differences using remarkable new seabed imagery. This bathymetric data provides unprecedented empirical evidence of confluence and subsequent separation of the last British and Fennoscandian Ice Sheets. Critically, it also allows a viable pattern of ice-sheet disintegration to be proposed for the first time. Covering the continental shelf around the northern United Kingdom, extensive echosounder data reveals striking geomorphic evidence -in the form of tunnel valleys and moraines -relating to the former British and Fennoscandian Ice Sheets. The pattern of tunnel valleys in the northern North Sea Basin and the presence of large moraines on the West Shetland Shelf, coupled with stratigraphic evidence from the Witch Ground Basin, all suggest that at its maximum extent a grounded ice sheet flowed from SE to NW across the northern North Sea Basin, terminating at the continental shelf edge. The zone of confluence between the British and much larger Fennoscandian Ice Sheets was probably across the northern Orkney Islands, with fast-flowing ice in the Fair Isle Channel focusing sediment delivery to the Rona and Foula Wedges. This period of maximum confluent glaciation (c. 30-25 ka BP) was followed by a remarkable period of large-scale ice-sheet re-organisation. We present evidence suggesting that as sealevel rose, a large marine embayment opened in the northern North Sea Basin, as far south as the Witch Ground Basin, forcing the two ice sheets to decouple rapidly along a north-south axis east of Shetland. As a result, both ice-sheets rapidly adjusted to new quasi-stable margin positions forming a second distinct set of moraines (c. 24-18 ka BP). The lobate overprinted morphology of these moraines on the mid-shelf west of Orkney and Shetland indicates that the re-organisation of the British Ice Sheet was extremely dynamic -probably dominated by a series of internally forced readvances. Critically, much of the ice in the low-lying North Sea Basin may have disintegrated catastrophically as decoupling progressed in response to rising sea levels. Final-stage deglaciation was marked by near-shore ice streaming and increasing topographic control on ice-flow direction. Punctuated retreat of the British Ice Sheet continued until c. 16 ka BP when, following the North Atlantic iceberg-discharge event (Heinrich-1), ice was situated at the present-day coastline in NW Scotland.

Timing of massive ‘Fleuve Manche’ discharges over the last 350kyr: insights into the European ice-sheet oscillations and the European drainage network from MIS 10 to 2

“…Because Late Weichselian ice sheets never reached the English Channel area (Ehlers and Gibbard, 2004), we conclude that the Rhine-Thames drainage, which was a conduit for sediment-laden meltwater from the BIIS, FIS and the Alpine glaciers, flowed via the Dover Strait into the Bay of Biscay at the end of the last glacial period, confirming previous proposals by Gibbard (1988) and Busschers et al (2007). Coalescence of the BIIS and FIS in the North Sea basin is proposed for the last glacial period (Sejrup et al, 1994;Sejrup et al, 2000;Carr et al, 2006;Graham et al, 2007;Bradwell et al, 2008;Sejrup et al, in press) and we assume that the southwards-directed drainage pattern described originates from this glacial configuration. The significant increase of terrigenous flux detected at ca.…”

On the reconstruction of palaeo-ice sheets: Recent advances and future challenges

“…In the last decade alone, there are cases where margins have been revised and extended to the edge of the continental shelf for the Laurentide and Innuitian Ice Sheets, the Eurasian Ice Sheet (including the Fennoscandian, Barents Sea and British-Irish Ice Sheets), and the Greenland Ice Sheet (e.g. Ottesen et al, 2005;Shaw et al, 2006;Bradwell et al, 2008;England et al, 2009;Ó Cofaigh et al, 2013). In particular, advances in high-latitude seafloor mapping in the 1990s, especially high resolution multibeam mapping, have helped elucidate the glacial history of the Arctic Ocean (reviewed in Jakobsson et al, 2014).…”

Quaternary evolution of glaciated gneiss terrains: pre-glacial weathering vs. glacial erosion

“…Cosmogenic isotope exposure ages show that high elevation areas (> 800 m) had deglaciated by ~ 16 ka BP (Fabel et al, 2012). However, the timing of Late-Devensian deglaciation of the low ground is still debated and is the subject of continuing research (Bradwell et al, 2008b;Stoker et al, 2009;Ballantyne and Stone, 2011). Glaciation during the Younger Dryas (13-11 ka BP) resulted in the development of ice caps and local cirque glaciers on high ground, but ice cover at this time did not reach the low ground within the study area (Lawson, 1986;Benn and Lukas, 2006;Bradwell, 2006).…”