23 Jun 2022
23 Jun 2022
Status: this preprint is currently under review for the journal TC.

The collapse of the Laurentide-Cordilleran ice saddle and early opening of the Mackenzie Valley, Northwest Territories, constrained by 10Be exposure dating

Benjamin J. Stoker1, Martin Margold1, John C. Gosse2, Alan J. Hidy3, Alistair J. Monteath4, Joseph M. Young4, Niall Gandy5,6, Lauren J. Gregoire6, Sophie L. Norris7, and Duane Froese4 Benjamin J. Stoker et al.
  • 1Department of Physical Geography and Geoecology, Charles University, Albertov 6, 12843 Praha 2, Czech Republic
  • 2Department of Earth Sciences, Dalhousie University, 1355 Oxford Street, Halifax B3H 4R2, Nova Scotia, Canada
  • 3Centre for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, USA
  • 4Department of Earth and Atmospheric Sciences, 1-26 Earth Sciences Building, University of Alberta, Edmonton T6G 2E3, Alberta, Canada
  • 5Department of Natural and Built Environment, Sheffield Hallam University, Sheffield, United Kingdom, S1 1WB
  • 6School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK
  • 7Department of Geography, David Turpin Building, University of Victoria, Victoria, V8P 5C2, British Columbia, Canada

Abstract. Deglaciation of the northwestern Laurentide Ice Sheet in the central Mackenzie Valley opened the northern portion of the deglacial Ice-Free Corridor between the Laurentide and Cordilleran ice sheets and a drainage route to the Arctic Ocean. In addition, ice-sheet saddle collapse in this section of the Laurentide Ice Sheet has been implicated as a mechanism for delivering substantial freshwater influx into the Arctic Ocean on centennial timescales. However, there is little empirical data to constrain the deglaciation chronology in the central Mackenzie Valley where the northern slopes of the ice saddle were located. Here, we present 30 new 10Be cosmogenic nuclide exposure dates across six sites, including two elevation transects, which constrain the timing and rate of thinning of the Laurentide Ice Sheet from the area. Our new 10Be dates indicate that the initial deglaciation of the eastern summits of the central Mackenzie Mountains began at ~15.8 ka (17.1 – 14.6 ka), ~1,000 years earlier than previous reconstructions. The main phase of ice-saddle collapse occurred between ~14.9 and 13.2 ka, consistent with numerical modelling simulations, placing this event within the Bølling–Allerød interval (14.6 – 12.9 ka). Our new dates require a revision of ice margin retreat dynamics, with ice retreating more easterly rather than southward along the Mackenzie Valley. In addition, we quantify a total sea-level rise contribution from the Cordilleran-Laurentide ice saddle region of ~11.2 m between 16 ka and 13 ka.

Benjamin J. Stoker et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2022-120', Anonymous Referee #1, 05 Aug 2022
  • RC2: 'Comment on tc-2022-120', Anonymous Referee #2, 19 Aug 2022

Benjamin J. Stoker et al.

Benjamin J. Stoker et al.


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Short summary
During the last glaciation, the Laurentide Ice Sheet was the largest of the Northern Hemisphere ice sheets. In northern Canada, it covered the Mackenzie Valley, altering the drainage systems and blocking species migration between North America and Beringia. Here we reconstruct the deglaciation of the Laurentide Ice Sheet in the Mackenzie Valley region and discuss the implications for the migration of early humans into North America, the drainage of glacial lakes, and past sea-level rise.