The timing and consequences of the blockage of the Humber Gap by the last British−Irish Ice Sheet

Abstract

The eastern England terrestrial glacial sequences are critical to the spatial and temporal reconstruction of the last British−Irish Ice sheet (BIIS). Understanding glacial behaviour in the area of the Humber Gap is key as its blockage by ice created extensive proglacial lakes. This paper maps the glacial geomorphology of the Humber Gap region to establish for the first time the extent and thickness of the North Sea Lobe (NSL) of the BIIS. Findings establish the westerly maximal limit of the NSL. Ten new luminescence ages from across the region show the initial Skipsea Till advance to the maximal limits occurred regionally at c. 21.6 ka (Stage 1) and retreated off‐shore c. 18 ka (Stage 2). Punctuated retreat is evident in the south of the region whilst to the immediate north retreat was initially rapid before a series of near synchronous ice advances (including the Withernsea Till advance) occurred at c. 16.8 ka (Stage 3). Full withdrawal of BIIS ice occurred prior to c. 15 ka (Stage 4). Geomorphic mapping and stratigraphy confirms the existence of a proto Lake Humber prior to Stage 1, which persisted to Stage 3 expanding eastward as the NSL ice retreated. It appears that proglacial lakes formed wherever the NSL encountered low topography and reverse gradients during both phases of both advance and retreat. These lakes may in part help explain the dynamism of parts of the NSL, as they initiated ice draw down and associated streaming/surging. The above record of ice‐dammed lakes provides an analogue for now off‐shore parts of the BIIS where it advanced as a number of asynchronous lowland lobes.

The mixed‐bed glacial landform imprint of the North Sea Lobe in the western North Sea

“…These dates are supported by new OSL dates on glacial outwash from Seaham on the Durham coast which suggest final deglaciation after~19.6 ka, as the western margin of the NSL migrated north (Table II). These dates are somewhat earlier (although within errors) than OSL dates from the Yorkshire region (17.6-17 ka; Bateman et al, 2017;Evans et al, 2017) hence further dating control (or recalibration) is required between Lincolnshire, Yorkshire, Durham and Northumberland in order to fully reconcile overall NSL recession rates. However, it is clear from the location of W1 that the NSL had unzipped from the Eden-Stainmore Ice Stream by~19.5 ka, and furthermore, cosmogenic dates west of Newcastle also imply the Tyne gap Ice Stream decoupled from the NSL beforẽ 17.8 ka (Livingstone et al, 2015).…”

“…That final phase of NSL advance to the south was followed by ice recession and Dove et al (2017) and Roberts et al (2018) chart a series of large arcuate, lobate moraines formed as the NSL margin migrated north, parallel with the Lincolnshire and Yorkshire coasts ( Figure 17). As the ice retreated northwards, Bateman et al (2017) constrain final deglaciation of East Yorkshire coast to >17 ka based on OSL ages relating to the final stages of Glacial Lake Humber at Hemingborough and Ferrybridge and post-glacial sediments found at Barmston and Sewerby (Figure 17). Slightly further north in the Vale of Pickering, Evans et al (2017) suggest the NSL thinned and receded offshore from the Yorkshire coast at~17.6 ka based on ages from Heslerton.…”

“…As such it was an area characterised by complex ice sheet dynamics resulting from ice sheet coalescence, decoupling, ice divide migration, marine inundation and the switching on and off of ice streams (Graham et al, 2007(Graham et al, , 2011Sejrup et al, 2016;Patton et al, 2017). The vast majority of the evidence for the NSL has been derived from onshore glaciogenic sediment exposures, ice marginal geomorphology and palaeoice dammed lakes (Wood and Rome, 1868;Lamplugh, 1879, Bisat, 1932Eyles et al, 1982;Evans et al, 1995;Catt, 2007;Bateman et al, 2008Bateman et al, , 2011Bateman et al, , 2015Bateman et al, , 2017Evans and Thomson, 2010;Davies et al, 2009Davies et al, , 2012aRoberts et al, 2013), however, few studies (with the exception of Davies et al, 2011;Dove et al, 2017) have focused on the offshore imprint of the NSL. The vast majority of the evidence for the NSL has been derived from onshore glaciogenic sediment exposures, ice marginal geomorphology and palaeoice dammed lakes (Wood and Rome, 1868;Lamplugh, 1879, Bisat, 1932Eyles et al, 1982;Evans et al, 1995;Catt, 2007;Bateman et al, 2008Bateman et al, , 2011Bateman et al, , 2015Bateman et al, , 2017Evans and Thomson, 2010;Davies et al, 2009Davies et al, , 2012aRoberts et al, 2013), however, few studies (with the exception of Davies et al, 2011;…”

“…A particularly intriguing glaciological attribute of ice sheet inundation of the NSB was the formation of the North Sea Lobe (NSL), nourished by ice emanating from Northern England and Scotland, flowing south and parallel to the English east coast and periodically surging (Boulton et al, 1977;Eyles et al, 1994;Boston et al, 2010) (Figure 1). The vast majority of the evidence for the NSL has been derived from onshore glaciogenic sediment exposures, ice marginal geomorphology and palaeoice dammed lakes (Wood and Rome, 1868;Lamplugh, 1879, Bisat, 1932Eyles et al, 1982;Evans et al, 1995;Catt, 2007;Bateman et al, 2008Bateman et al, , 2011Bateman et al, , 2015Bateman et al, , 2017Evans and Thomson, 2010;Davies et al, 2009Davies et al, , 2012aRoberts et al, 2013), however, few studies (with the exception of Davies et al, 2011;Dove et al, 2017) have focused on the offshore imprint of the NSL.…”

Can glacial shearing of sediment reset the signal used for luminescence dating?

“…As many glacial sediments will have been in the shearing zone for distance greatly exceeding that of this ring-shearing experiment, reset grains in many glacial diamicts and landforms may be more prevalent than previously thought. This may account for the relatively good resetting of sediment associated with glacial landforms that have been obtained as part of the BRITICE-CHRONO project (e.g., Evans et al, 2017;Smedley et al, 2017;Bateman et al, 2018). That many glacial studies have struggled in this regard may be more because of insensitive quartz and poor intrinsic OSL characteristics of local bedrocks (e.g., Sawakuchi et al, 2011;Klasen et al, 2016) than to lack of signal resetting.…”