Marine‐Calibrated Chronology of Southern Laurentide Ice Sheet Advance and Retreat: ∼2,000‐Year Cycles Paced by Meltwater–Climate Feedback

Abstract

Warming climate (Badgeley et al., 2020) associated with increasing northern-hemisphere summer insolation (Berger, 1978) triggered widespread ice retreat and the end of the global Last Glacial Maximum (LGM), approximately 19.5 ka (kiloannum: thousand calendar years before "present," BP, at 1950) (Clark et al., 2009). Laurentide Ice Sheet (LIS) meltwater produced ∼63 m of global sea-level rise (Gowan et al., 2021)-approximately equal to the volume of all present-day ice masses combined-but the LIS did not smoothly retreat. Instead, the onset of deglaciation triggered repeated cycles of 150-400 km of ice retreat and readvance through the Great Lakes region (e.g., Licciardi et al., 1999;Mickelson & Colgan, 2003) (Figure 1: bases of black arrows).