Rapid ice sheet retreat triggered by ice stream debuttressing: Evidence from the North Sea

Abstract

Using high-resolution bathymetric and shallow seismic data from the North Sea, we have mapped hitherto unknown glacial landforms that connect and resolve longstanding gaps in the Quaternary geological history of the basin. We use these data combined with published information and dates from sediment cores to reconstruct the extent of the Fennoscandian and British Ice Sheets (FIS and BIS) in the North Sea during the last phases of the last glacial stage. It is concluded that the BIS occupied a much larger part of the North Sea than previously suggested and that North Sea ice underwent a dramatic disintegration ~18,500 yr ago. This was triggered by grounding-line retreat of the Norwegian Channel Ice Stream, which debuttressed adjacent ice masses, and led to an unzipping of the BIS and FIS accompanied by drainage of a large ice-dammed lake. Our reconstruction of events provides an opportunity to improve understanding and modeling of the disintegration of marine-based ice sheets, and the complex interplay between ocean circulation and the cryosphere.

Middle to Late Devensian glaciation of north‐east Scotland: implications for the north‐eastern quadrant of the last British–Irish ice sheet

“…The ice shed positioned between Buchan and Shetland possibly migrated farther to the east by the end of this stage, drawing ice north-westwards across the Witch Ground Basin (WGB) in accord with the flowsets identified there by Graham et al (2007) and Bradwell et al 2008 (Figure 9.3.2), but other scenarios are possible (Sejrup et al, 2016). The stage probably equates with the widespread dramatic thinning and drawdown of ice that affected at least the SW sector of the last BIIS during Greenland Interstadial (GI) 2 at c.23 ka (Scourse et al 2009).…”

“…Although a scenario of a second maximum to the last ice sheet on northern Scotland appears to be in conflict with the onset of ice-free conditions in the WGB, Sejrup et al (2016) now suggest that reworked marine shells in glaciomarine deposits may relate to periods of ice withdrawal from the WGB at 27-25.5 ka, after 18 ka, and during intervening periods.…”

“…High-resolution seismic data, bathymetric records and dates on shells taken from sediment cores suggest that the basin was glaciated early in the last glaciation, between c.33k and 27k cal a BP (Sejrup et al, 2015) after which it became a shallow marine embayment with connections to the Atlantic Ocean east of Shetland and possibly the Norwegian Channel . We note, however, that the radiocarbon dates for shells in borehole 77/2 in the WGB span 9,000 years (Sejrup et al, 2015) and that reworking of shells from multiple ice-free periods would allow intervening periods of ice cover between 26.6k and 17.7k cal a BP (Sejrup et al, 2016).…”

“…This 'Atlantic Shelf Glaciation' at c. 32-25k cal a BP (Sejrup et al, , 2005, or 32-27k cal a BP (Sejrup, 2015), was followed by the growth of more restricted ice sheets after c. 22k cal a BP. However, doubts surround the published geochronometry and it is difficult to explain why early deglaciation of the central NSB occurred during a period including the global LGM when other sectors of the BIIS were expanding Sejrup et al, 2016). It is generally agreed that the northern sector of the last BIIS built up towards the end of MIS 3, after c. 32k a BP, when ice extended to the continental shelf margin (Stoker and Holmes, 1991;Whittington and Hall, 2002;Wilson et al, 2002;Bradwell et al, 2008;Jacobi et al, 2009;Chiverrell and Thomas, 2010;Gibbard and Clark, 2011;Graham et al, 2011;Clark et al, 2012;Everest et al, 2013;Hughes et al, 2014Hughes et al, , 2016Hiemstra et al, 2015;Bradwell and Stoker, 2015a).…”

“…This stage is probably contemporaneous with the creation of the Tampen Ridge, at the western margin of the Norwegian Channel (Figure 1), during the Tampen Stadial of Sejrup et al (2000) and the global LGM of Mix et al (2001) between c. 22 and 19k cal a BP. The BIIS and SIS probably eventually re-coalesced when a shelf-edge parallel ice sheet regrew across Orkney and Shetland (Sejrup et al, 2014;Sejrup et al, 2016;Hall et al, 2016) (Figure 9.4). If so, the central NSB either became reoccupied by ice or an ice-locked, seasonally frozen lake.…”