Timing of Cordilleran-Laurentide ice-sheet separation: Implications for sea-level rise

During the last deglaciation, collapse of the saddle between the North American Cordilleran and Laurentide ice sheets led to rapid ice-sheet mass loss and separation, with meltwater discharge contributing to deglacial sea-level rise. We directly date ice-sheet separation at the end of the saddle collapse using 64 Be-10 exposure ages along an similar to 1200-km transect of the ice-sheet suture zone. Collapse began in the south by 15.4 +/- 0.4 ka and ended by 13.8 +/- 0.1 ka at similar to 56 degrees N. Ice-sheet model simulations consistent with the Be-10 ages find that the saddle collapse contributed 6.2-7.2 m to global mean sea-level rise from similar to 15.5 ka to similar to 14.0 ka, or approximately one third of global mean sea-level rise over this period. We determine 3.1-3.6 m of the saddle collapse meltwater was released during Meltwater Pulse 1A similar to 14.6-14.3 ka, constituting 20-40% of this meltwater pulse's volume. Because the separation of the Cordilleran and Laurentide ice sheets occurred over 1-2 millennia, the associated release of meltwater during the saddle collapse supplied a smaller contribution to the magnitude of Meltwater Pulse 1A than has been recently proposed.