Abstract
The timing of Laurentide Ice Sheet deglaciation along its southwestern margin controlled the evolution of large glacial lakes and has implications for human migration into the Americas. Accurate reconstruction of the ice sheet's retreat also constrains glacial isostatic adjustment models and is important for understanding ice-sheet sensitivity to climate forcing.
Despite its significance, retreat of the southwestern Laurentide Ice Sheet (SWLIS) is poorly constrained by minimum-limiting C-14 data. We present 26 new cosmogenic Be-10 exposure ages spanning the western Interior Plains, Canada.
Using a Bayesian framework, we combine these data with geomorphic mapping, Be-10, and high-quality minimum-limiting C-14 ages to provide an updated chronology. This dataset presents an internally consistent retreat record and indicates that the initial detachment of the SWLIS from its convergence with the Cordilleran Ice Sheet began by ca. 15.0 ka, concurrent with or slightly prior to the onset of the Bolling-Allerod interval (14.7-12.9 ka) and retreated >1200 km to its Younger Dryas (YD) position in similar to 2500 yr.
Ice-sheet stabilization at the Cree Lake Moraine facilitated a meltwater drainage route to the Arctic from glacial Lake Agassiz within the YD, but not necessarily at the beginning. Our record of deglaciation and new YD constraints demonstrate deglaciation of the Interior Plains was similar to 60% faster than suggested by minimum C-14 constraints alone.
Numerical modeling of this rapid retreat estimates a loss of similar to 3.7 m of sea-level equivalent from the SWLIS during the Bolling-Allerod interval.