In this section, we discuss the evidence for the last British-Irish Ice Sheet (BIIS). Throughout the Quaternary (the last 2.6 million years), there have been many ice sheets in Britain. The ice sheet grows during cold periods (stadials) and recedes in warm periods (interstadials) like the one we live in today. The last BIIS began to grow after the last interglacial ended (125,000 years ago).
Last Glacial Maximum
The BIIS was at its maximum around 27,000 years ago and stretched from the continental shelf on its northern margin to South Wales, north Norfolk and the Vale of York. It had sufficient ice volume to raise global sea levels by about 2.5 m when it melted (Clark et al., 2012). We term this the “Last Glacial Maximum”.
We know about the pattern of and dynamics the British-Irish Ice Sheet because of the landforms it left behind. These include moraines, meltwater channels, eskers and drumlins. Researchers have compiled large databases of the these landforms (the BRITICE datasets), which you can explore on the BRITICE V2 map.
Large parts of the ice sheet were marine-based (grounded on land below sea level and terminating in the ocean) and drained by ice streams (Clark et al., 2012), making the last British-Irish Ice Sheet similar in many ways to the West Antarctic Ice Sheet today.
The last British-Irish Ice Sheet deglaciated in response to rising sea levels (driven by the melting of other ice masses) and rising temperatures, which are factors that are affecting the West Antarctic Ice Sheet today.
Deglaciation of the last British-Irish Ice Sheet
As the ice sheet melted, it separated into a number of smaller ice caps on higher ground. By 23,000 years ago, the ice sheet withdrew along its northern boundaries, but the southern boundary expanded. Ice streaming began down the Irish Sea, and ice lobes advanced into the Cheshire Basin, Vale of York and east coast of England (the North Sea Lobe) (Clark et al., 2012).
By 19,000 years ago, the ice sheet was rapidly shrinking. Final disintegration of the marine-based sectors occurred by 17,000 years ago, with most ice margins back onshore (Clark et al., 2012). By 16,000 years ago, the Scottish and Irish ice sheets had separated.
The Younger Dryas Readvance
An abrupt period of intense cold drove a readvance of glaciers from 12,900 to 11,700 years ago. This was the Younger Dryas Stadial; in Britain, this is commonly referred to as the Loch Lomond Readvance.
During this period, there was a small ice cap centered on the Scottish mountains, and small ice caps on mountains in the Lake District, North Wales, and the Brecon Beacons (Bickerdike et al., 2018).
This glaciation left behind a series of moraine ridges, flutings, hummocky moraine, meltwater channels, and shorelines from ice-dammed lakes that help us to understand this abrupt return to glacial conditions.
Climate warmed rapidly after 11,700 years ago, forcing the rapid collapse of the Younger Dryas ice cap in Scotland and recession of the smaller glaciers in the Lake District, Wales and on mountains in Scotland. This was the start of the Holocene, the warm period in which we currently live.
Bickerdike, H. L., Evans, D. J. A., Stokes, C. R., & Ó Cofaigh, C. (2018). The glacial geomorphology of the Loch Lomond (Younger Dryas) Stadial in Britain: a review. Journal of Quaternary Science, 33(1), 1–54. https://doi.org/doi:10.1002/jqs.3010
Clark, C. D., Hughes, A. L. C., Greenwood, S. L., Jordan, C., & Sejrup, H. P. (2012). Pattern and timing of retreat of the last British-Irish Ice Sheet. Quaternary Science Reviews, 44(0), 112–146. https://doi.org/10.1016/j.quascirev.2010.07.019
Scourse, J. D., Ward, S. L., Wainwright, A., Bradley, S. L., & Uehara, K. (2018). The role of megatides and relative sea level in controlling the deglaciation of the British–Irish and Fennoscandian ice sheets. Journal of Quaternary Science, 33(2), 139–149. https://doi.org/10.1002/jqs.3011