Ice flow dynamics of the northwestern Laurentide Ice Sheet during the last deglaciation

Stoker, Benjamin J.; Dulfer, Helen E.; Stokes, Chris R.; Brown, Victoria H.; Clark, Christopher D.; O'Cofaigh, Colm; Evans, David J.A.; Froese, Duane; Norris, Sophie L.; Margold, Martin

Abstract

Reconstructions of palaeo-ice stream activity provide an insight into the processes governing ice stream evolution over millennial timescales. The northwestern sector of the Laurentide Ice Sheet experienced a period of rapid retreat driven by warming during the Bølling–Allerød (14.7 – 12.9 ka) which may have contributed significantly to global mean sea level rise during this time. Therefore, the northwestern Laurentide Ice Sheet provides an opportunity to investigate ice sheet dynamics during a phase of rapid ice sheet retreat. Here, we classify coherent groups of ice flow parallel lineations into 326 flowsets and then categorise them as ice stream, deglacial, inferred deglacial or event type flowsets. Combined with ice marginal landforms and a new ice margin chronology (Dalton et al., 2023), we present the first reconstruction of ice flow dynamics of the northwestern Laurentide Ice Sheet at 500-year timesteps through the last deglaciation (17.5 – 10.5 ka). At the local Last Glacial Maximum (17.5 ka), the ice stream network was dominated by large, marine-terminating ice streams (>1000 km long) that were fed by the Laurentide-Cordilleran ice saddle to the south and the Keewatin Ice Dome to the east. As the ice margin retreated onshore, the drainage network was characterised by shorter, land-terminating ice streams (<200 km long), with the exception of the Bear Lake and Great Slave Lake ice streams (~600 km long) that terminated in large glacial lakes. Rapid reorganisation of the ice drainage network, from predominantly northerly ice flow to westerly ice flow, occurred over ~2000 years, coinciding with a period of rapid ice sheet surface lowering in the ice saddle region. We note a peak in ice stream activity during the Bølling–Allerød that we suggest is a result of increased ablation and a steepening of the ice surface slope in ice stream onset zones and the increase in driving stresses which contributed to rapid ice drawdown. The subsequent cessation of ice stream activity by the end of the Bølling–Allerød was a result of ice drawdown lowering the ice surface profile, reducing driving stresses and leading to widespread ice stream shut-down.

Citation

Stoker, B. J., Dulfer, H. E., Stokes, C. R., Brown, V. H., Clark, C. D., O'Cofaigh, C., Evans, D. J., Froese, D., Norris, S. L., & Margold, M. (2025). Ice flow dynamics of the northwestern Laurentide Ice Sheet during the last deglaciation. The Cryosphere, 19(2), 869–910. https://doi.org/10.5194/tc-19-869-2025

• Journal Article Type: Article
• Acceptance Date: Dec 16, 2024
• Online Publication Date: Feb 26, 2025
• Publication Date: 2025-02
• Deposit Date: Dec 17, 2024
• Publicly Available Date: Feb 26, 2025
• Journal: The Cryosphere
• Print ISSN: 1994-0416
• Electronic ISSN: 1994-0424
• Publisher: Copernicus Publications
• Peer Reviewed: Peer Reviewed
• Volume: 19
• Issue: 2
• Pages: 869–910
• DOI: https://doi.org/10.5194/tc-19-869-2025
• Public URL: https://durham-repository.worktribe.com/output/3223375
• Publisher URL: https://www.the-cryosphere.net/
• Additional Information: Preprint available at: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-137/