Retreat dynamics of the eastern sector of the British–Irish Ice Sheet during the last glaciation

Abstract

The findings of BRITICE‐CHRONO Transect 2 through the North Sea Basin and eastern England are reported. We define ice‐sheet marginal oscillation between ~31 and 16 ka, with seven distinctive former ice‐sheet limits (L1–7) constrained by Bayesian statistical analysis. The southernmost limit of the North Sea Lobe is recorded by the Bolders Bank Formation (L1; 25.8–24.6 ka). L2 represents ice‐sheet oscillation and early retreat to the northern edge of the Dogger Bank (23.5–22.2 ka), with the Garret Hill Moraine in north Norfolk recording a significant regional readvance to L3 at 21.5–20.8 ka. Ice‐marginal oscillations at ~26–21 ka resulted in L1, L2 and L3 being partially to totally overprinted. Ice‐dammed lakes related to L1–3, including Lake Humber, are dated at 24.1–22.3 ka. Ice‐sheet oscillation and retreat from L4 to L5 occurred between 19.7 and 17.3 ka, with grounding zone wedges marking an important transition from terrestrial to marine tidewater conditions, triggered by the opening of the Dogger Lake spillway between 19.9 and 17.5 ka. L6 relates to ice retreat under glacimarine conditions and final ice retreat into the Firth of Forth by 15.8 ka. L7 (~15 ka) represents an ice retreat from Bosies Bank into the Moray Firth.

Collapse of the Last Eurasian Ice Sheet in the North Sea Modulated by Combined Processes of Ice Flow, Surface Melt, and Marine Ice Sheet Instabilities

“…The Automated Timing Accordance Tool (ATAT) (Ely et al, 2019a(Ely et al, , 2019b) is used to identify matches between modeled deglaciation ages and geochronological data (in calibrated years before present). Geochronological dates with a quality control rating of Green or Amber by Small et al (2017) were used, along with additional offshore dates from (Bateman et al, 2018;Bradwell et al, 2021;Callard et al, 2018;Evans et al, 2018Evans et al, , 2019Evans et al, , 2021Roberts et al, 2018Roberts et al, , 2019, resulting in 131 geochronological dates for comparison with modeled deglaciation ages. ATAT calculates the wRMSE between modeled deglaciation ages and geochronological data, accounting for the uneven spatial distribution of dates.…”

Timing, pace and controls on ice sheet retreat: an introduction to the BRITICE‐CHRONO transect reconstructions of the British–Irish Ice Sheet

“…This is done with new Bayesian modelling of geochronosequences to produce coherent and definitive syntheses of palaeogeographic reconstructions of the back‐stepping ice margins across the marine to terrestrial transition. These results on the timing and pacing of ice withdrawal are then used to understand the main controls that drove or modulated ice sheet retreat (Benetti et al ., 2021; Bradwell et al ., 2021a,b; Chiverrell et al ., 2021; Evans et al ., 2021; Ó Cofaigh et al ., 2021; Scourse et al ., 2021). A further paper reports on how ice sheet modelling experiments and empirical data can be used in combination (Ely et al ., 2021), and another probes the glaciological meaning of ice‐rafted debris (Wilton et al ., 2021).…”

“…In the transect overview paper, Evans et al . (2021) report some new dates and use the two Bayesian transects to analyse a total of 68 BRITICE‐CHRONO dates (53 OSL and 15 radiocarbon) and 37 legacy dates to build a reconstruction of ice margin extent and retreat. Key questions answered by the reconstruction include: how far did British ice extend?…”

“…The Gowan plastic ICESHEET model (Gowan et al ., 2016) was fitted to the BRITICE‐CHRONO and Scandinavian DATED (Hughes et al ., 2016) ice limits to provide mass loading estimates for use in northen hemispheric GIA modelling to better constrain relative sea level variations. These data have informed four of our transect papers (Ó Cofaigh et al ., 2021; Evans et al ., 2021; Scourse et al ., 2021; Benetti et al ., 2021), have been used in a GIA modelling investigation on fingerprinting of Meltwater Pulse 1A (Lin et al ., 2021), and used in a project forecasting 21st century sea levels around Britain and northwestern Europe, the UKCP18 Marine Report (Palmer et al ., 2018). The Parallel Ice Sheet Model (PISM, Winkelmann et al ., 2011) has been heavily used, in one case nudged towards fitting the BRITICE‐CHRONO ice limits and in another case with ensemble runs independent of them and then tested against them.…”

“…(2019) ran experiments to explore the extent to which the BISICLES model could correctly simulate the location and evolution of ice streams compared against the evidence. Finally, it has been run (Gandy et al ., 2021) to assesss the physical plausibility of an empirically reconstructed ice collapse event over the North Sea (Sejrup et al ., 2016; Evans et al ., 2021). This involved choosing between 70 ensemble experiments using quantitative model–data comparison tools finding the best match regarding ice flow directions, margin positions and satisfying the new deglacial age dates.…”