A critical re-analysis of constraints on the timing and rate of Laurentide Ice Sheet recession in the northeastern United States

We review geochronological data relating to the timing and rate of Laurentide Ice Sheet recession in the northeastern United States and model ice margin movements in a Bayesian framework using compilations of previously published organic ¹⁴C (n = 133) and in situ cosmogenic ¹⁰Be (n = 95) ages. We compare the resulting method-specific chronologies with glacial varve records that serve as independent constraints on the pace of ice recession to: (1) construct a synthesis of deglacial chronology throughout the region; and (2) assess the accuracy of each chronometer for constraining the timing of deglaciation. Near the Last Glacial Maximum terminal moraine zone, ¹⁰Be and organic ¹⁴C ages disagree by thousands of years and limit determination of the initial recession to a date range of 24–20 ka. We infer that ¹⁰Be inherited from pre-glacial exposure adds 2–6 kyr to many exposure ages near the terminal moraines, whereas macrofossil ¹⁴C ages are typically 4–8 kyr too young due to a substantial lag between ice recession and sufficient organic material accumulation for dating in some basins. Age discrepancies between these chronometers decrease with distance from the terminal moraine, due to less ¹⁰Be inherited from prior exposure and a reduced lag between ice recession and organic material deposition. ¹⁴C and ¹⁰Be ages generally agree at locations more than 200 km distal from the terminal moraines and suggest a mostly continuous history of ice recession throughout the region from 18 to 13 ka with a variable pace best documented by varves.