Abstract
The Laurentide Ice Sheet was the largest global ice mass to grow and decay during the last glacial cycle (~115 ka to ~10 ka). Despite its importance for driving major changes in global mean sea level, long-term landscape evolution, and atmospheric circulation patterns, the history of the Laurentide (and neighbouring Innuitian) Ice Sheet is poorly constrained owing to sporadic preservation of stratigraphic records prior to the Last Glacial Maximum (LGM; ~25 ka) and a case-study approach to the dating of available evidence. Here, we synthesize available geochronological data from the glaciated region, together with published stratigraphic and geomorphological data, as well as numerical modelling output, to derive 19 hypothesised reconstructions of the Laurentide and Innuitian ice sheets from 115 ka to 25 ka at 5-kyr intervals, with uncertainties quantified to include best, minimum, and maximum ice extent estimates at each time-step. Our work suggests that, between 115 ka and 25 ka, some areas of North America experienced multiple cycles of rapid ice sheet growth and decay, while others remained largely ice-free, and others were continuously glaciated. Key findings include: (i) the growth and recession of the Laurentide Ice Sheet from 115 ka through 80 ka; (ii) significant build-up of ice to almost LGM extent at ~60 ka; (iii) a potentially dramatic reduction in North American ice at ~45 ka; (iv) a rapid expansion of the Labrador Dome at ~38 ka; and (v) gradual growth toward the LGM starting at ~35 ka. Some reconstructions are only loosely constrained and are therefore speculative (especially prior to 45 ka). Nevertheless, this work represents our most up-to-date understanding of the build-up of the Laurentide and Innuitian ice sheets during the last glacial cycle to the LGM based on the available evidence. We consider these ice configurations as a series of testable hypotheses for future work to address and refine. These results are important for use across a range of disciplines including ice sheet modelling, palaeoclimatology and archaeology and are available digitally.
Highlights
The North American ice sheet complex was the largest global ice mass to grow and recede during the last glacial cycle (~115 ka to ~10 ka)
We describe our best estimate of the ice margin, followed by estimates of minimum and maximum ice extents
We pre sent a brief comparison between our ice margin reconstructions and estimates of GMSL (Pico et al, 2017; Spratt and Lisiecki, 2016), as well as modelled work on North American ice sheet history, notably the work of Stokes et al (2012), Bahadory et al (2021) and Gowan et al (2021)
Summary
The North American ice sheet complex (consisting of the Laurentide, Cordilleran and Innuitian ice sheets; Fig. 1) was the largest global ice mass to grow and recede during the last glacial cycle (~115 ka to ~10 ka). The last glacial cycle (known as the Wisconsinan Stade in North America) comprised the growth, evo lution and recession of continental ice that took place between the largely ice-free Marine Isotope Stage 5e (MIS 5e; ~125 ka) and the Holocene (~12 ka to present-day). Best understood is the interval from ~25 ka to present-day, when the North American ice sheet complex deglaciated from its maximum LGM extent and left behind an abundance of sediments and landforms from which to reconstruct and date its recession (Dalton et al, 2020; Dyke, 2004; Dyke and Prest, 1987; Fulton, 1989; Stokes, 2017). Prior to the LGM, the history of continental ice over North
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