Rapid Holocene Deglaciation of the Labrador Sector of the Laurentide Ice Sheet

Retreat of the Laurentide Ice Sheet (LIS) following the Last Glacial Maximum 21 000 yr BP affected regional to global climate and accounted for the largest proportion of sea level rise. Although the late Pleistocene LIS retreat chronology is relatively well constrained, its Holocene chronology remains poorly dated, limiting our understanding of its role in Holocene climate change and sea level rise. Here new Be cosmogenic exposure ages on glacially deposited boulders are used to date the final disappearance of the Labrador sector of the LIS (LS-LIS). These data suggest that following the deglaciation of the southeastern Hudson Bay coastline at 8.0 0.2 cal ka BP, the southwestern margin of the LS-LIS rapidly retreated 600 km in 140 yr and most likely in 600 yr at a rate of 900 m yr , with final deglaciation by 6.8 0.2 Be ka. The disappearance of the LS-LIS 6.8 Be ka and attendant reduction in freshwater runoff may have induced the formation of Labrador Deep Seawater, while the loss of the high albedo surface may have initiated the Holocene Thermal Maximum in eastern Canada and southern Greenland. Moreover, the rapid melting just prior to 6.8 Be ka indicates that the remnant LIS may be the primary source of a postulated rapid rise in global sea level of 5 m that occurred sometime between 7.6 and 6.5 cal ka BP.