The BRITICE‐CHRONO consortium of researchers undertook a dating programme to constrain the timing of advance, maximum extent and retreat of the British–Irish Ice Sheet between 31 000 and 15 000 years before present. The dating campaign across Ireland and Britain and their continental shelves, and across the North Sea included 1500 days of field investigation yielding 18 000 km of marine geophysical data, 377 cores of sea floor sediments, and geomorphological and stratigraphical information at 121 sites on land; generating 690 new geochronometric ages. These findings are reported in 28 publications including synthesis into eight transect reconstructions. Here we build ice sheet‐wide reconstructions consistent with these findings and using retreat patterns and dates for the inter‐transect areas. Two reconstructions are presented, a wholly empirical version and a version that combines modelling with the new empirical evidence. Palaeoglaciological maps of ice extent, thickness, velocity, and flow geometry at thousand‐year timesteps are presented. The maximum ice volume of 1.8 m sea level equivalent occurred at 23 ka. A larger extent than previously defined is found and widespread advance of ice to the continental shelf break is confirmed during the last glacial. Asynchrony occurred in the timing of maximum extent and onset of retreat, ranging from 30 to 22 ka. The tipping point of deglaciation at 22 ka was triggered by ice stream retreat and saddle collapses. Analysis of retreat rates leads us to accept our hypothesis that the marine‐influenced sectors collapsed rapidly. First order controls on ice‐sheet demise were glacio‐isostatic loading triggering retreat of marine sectors, aided by glaciological instabilities and then climate warming finished off the smaller, terrestrial ice sheet. Overprinted on this signal were second order controls arising from variations in trough topographies and with sector‐scale ice geometric readjustments arising from dispositions in the geography of the landscape. These second order controls produced a stepped deglaciation. The retreat of the British–Irish Ice Sheet is now the world’s most well‐constrained and a valuable data‐rich environment for improving ice‐sheet modelling.
|Number of pages||59|
|Early online date||7 Sep 2022|
|Publication status||Published online - 7 Sep 2022|
This paper is dedicated to Richard Hindmarsh with much love, he died while the paper was in review. Without him the BRITICE‐CHRONO project would not have happened. This work was funded by the Natural Environment Research Council consortium grant BRITICE‐CHRONO NE/J009768/1 and by the NERC Radiocarbon Facility and the NERC Cosmogenic Isotope Analysis Facility. Thanks are due to the staff at the SUERC AMS Laboratory, East Kilbride for carbon and beryllium isotope measurements. Thanks are due to the technical staff at the Aberystwyth Luminescence Research Laboratory and the Sheffield Luminescence Laboratory. The project benefited from the PalGlac team of researchers with funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme to CDC (Grant Agreement No. 787263) and supporting SB and AI. JCE acknowledges support from a NERC independent fellowship award (NE/R014574/1). Many researchers are thanked for their generous discussions or help on fieldwork on land or at sea including: Arosio R., Cotterill, C., Davies, S., Gales, J., Greenwood, S., Grimoldi, E., Mellett, C., Morgan, S., Purcell, C., Roseby, Z., Schiele, K., Stewart, H., Tarlati, S., Weilbach, K., Wilton, D. For our research cruises, we are grateful to the crew of RRS and the technical and engineering support from the Marine Operations team of the British Geological Survey. We thank the PISM team of ice‐sheet modellers and Evan Gowan for ICESHEET, and note that the development of PISM was supported by NSF grants PLR‐1603799 and PLR‐1644277 and NASA grant NNX17AG65G. DP acknowledges funding from the Italian PNRA project IPY GLAMAR (grant number 2009/A2.15), and from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska‐Curie grant agreement no. 656821 (project SEAGAS). We are indebted to the numerous pubs and bars that lubricated our conversations of science and gave sustenance during fieldwork. Bethan Davies and Martin Margold are thanked for their helpful comments on a version of this paper, and Jan A. Piotrowski for his work as editor. James Cook
© 2022 The Authors. Boreas published by John Wiley & Sons Ltd on behalf of The Boreas Collegium.