The LGM British-Irish Ice Sheet: an introduction

What is the British-Irish Ice Sheet? | The Devensian British-Irish Ice Sheet | How do we know? | What’s in a name? | Activities | References | Comments

What is the British-Irish Ice Sheet?

The British-Irish Ice Sheet is a name given to ice sheets that covered Britain and Ireland at different times during the Quaternary Period. Evidence for at least three major ice sheets is preserved in the sedimentary record on land in Britain and Ireland. These were the Anglian (between 478,000 and 424,000 years ago), the Wolstonian (between 300,000 and 130,000 years ago) and the Devensian (approximately 27,000 years ago, during the Last Glacial Maximum)1. This article deals with the Devensian ice sheet.

The Devensian British-Irish Ice Sheet

The Devensian British-Irish Ice Sheet was a large mass of ice that covered approximately two thirds of Britain and Ireland around 27,000 years ago2. All of Scotland and Ireland, most of Wales, and most of the north of England was underneath the ice sheet during the Last Glacial Maximum. This ice sheet retreated and shrank after 27,000 years ago, and had completely disappeared by 11,300 years ago3.

The maximum extent of the Devensian British-Irish Ice Sheet, compiled from Sejrup et al., 20059, Bradwell et al., 200810 and Sejrup et al., 201611. Bathymetry data are from the GEBCO 2016 dataset (https://www.gebco.net/data_and_products/gridded_bathymetry_data/) and land elevation from the European Environment Agency EU-DEM (https://www.eea.europa.eu/data-and-maps/data/eu-dem)

The retreat of the British-Irish Ice Sheet was not constant across the entire ice sheet. Different sectors of the ice sheet retreated at different rates, due to different processes affecting the ice sheet margins. Ice margins in contact with the ocean retreated earlier and quicker than ice margins on land2. There was also a period of ice sheet regrowth, known as a readvance, during a period known as the Younger Dryas, also called the Loch Lomond stadial4.

How do we know?

The Devensian ice sheet is the best-understood of the past British-Irish Ice Sheets. Because it is the most recent, evidence for the Devensian ice sheet is well preserved. There is a strong imprint of this ice sheet in the glacial geology of Britain. Many glacial landforms record the story of movement of ice. In the mountains, erosional landforms, such as cirques and roches moutonées, are common. In the lowlands, the ice sheet has left behind sediment deposits, such as tills, and depositional landforms, such as drumlins and moraines.

Drumlins in Ribblesdale
Drumlins formed by the British-Irish Ice Sheet in Ribblesdale, Yorkshire. Their orientation shows ice flowed down the valley. Elevation data: OS Terrain 5 (https://www.ordnancesurvey.co.uk/business-government/products/terrain-5)

The British-Irish Ice Sheet has been studied for nearly 200 years5. This level of study means it is well understood. Knowing how this ice sheet behaved under a warming climate after the Last Glacial Maximum is important for understanding how present-day ice sheets will change in the future6.

What’s in a name?

The British-Irish Ice Sheet has been called many things in the past. Other names you might see are the British Ice Sheet5, the British Isles Ice Sheet7, and the Celtic Ice Sheet8. You might also see the Devensian Stage being referred to as the Late Pleistocene, the Weichselian Stage, or the Late Glacial. In Ireland, the ice sheet is known as the Midlandian stage, because it was historically thought to terminate in the Irish Midlands. Thanks Sam Roberson for that additional information!

Activities

Was the land your town is built on under the British-Irish Ice Sheet at the Last Glacial Maximum? Download the .zip file below and import the .kml into Google Earth. Explore which hills and mountain ranges the ice sheet covered. Look at the relationship of the British-Irish Ice Sheet with the water depth in the Atlantic Ocean. Think about areas that were not covered- why not?

References

1. Ehlers, J. & Gibbard, P. L. Quaternary Glaciations – Extent and Chronology: Part I – Europe. vol. 2 (Elsevier, 2004).

2. Clark, C. D., Hughes, A. L. C., Greenwood, S. L., Jordan, C. & Sejrup, H. P. Pattern and timing of retreat of the last British-Irish Ice Sheet. Quat. Sci. Rev. 44, 112–146 (2012).

3. Small, D. & Fabel, D. Was Scotland deglaciated during the Younger Dryas? Quat. Sci. Rev. 145, 259–263 (2016).

4. Bickerdike, H. L., Evans, D. J. A., Stokes, C. R. & Ó Cofaigh, C. The glacial geomorphology of the Loch Lomond (Younger Dryas) Stadial in Britain: a review. J. Quat. Sci. 33, 1–54 (2018).

5. Clark, C. D. et al. Map and GIS database of glacial landforms and features related to the last British Ice Sheet. Boreas 33, 359–375 (2004).

6. Gandy, N. et al. Marine Ice Sheet Instability and Ice Shelf Buttressing Influenced Deglaciation of the Minch Ice Stream, Northwest Scotland. Cryosph. Discuss. 1–24 (2018) doi:10.5194/tc-2018-116.

7. Boulton, G. & Hagdorn, M. Glaciology of the British Isles Ice Sheet during the last glacial cycle: form, flow, streams and lobes. Quat. Sci. Rev. 25, 3359–3390 (2006).

8. Hughes, A. L. C., Gyllencreutz, R., Lohne, Ø. S., Mangerud, J. & Svendsen, J. I. The last Eurasian ice sheets – a chronological database and time-slice reconstruction, DATED-1. Boreas 45, 1–45 (2016).

9. Sejrup, H. P. et al. Pleistocene glacial history of the NW European continental margin. Mar. Pet. Geol. 22, 1111–1129 (2005).

10. Bradwell, T. et al. The northern sector of the last British Ice Sheet: Maximum extent and demise. Earth-Science Rev. 88, 207–226 (2008).

11. Sejrup, H. P., Clark, C. D. & Hjelstuen, B. O. Rapid ice sheet retreat triggered by ice stream debuttressing: Evidence from the North Sea. Geology 44, 355–358 (2016).

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2 thoughts on “The LGM British-Irish Ice Sheet: an introduction

  1. In Ireland the last glacial cycle was referred to for a long time as the ‘Midlandian’. This was because the ice sheet was thought to terminate around the Irish Midlands. It is now known that the ice sheet was confluent with both the British Ice Sheet as well as the smaller ice dome centred on Cork and Kerry.

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