The history of ice-sheet retreat on North America during Termination 5: implications for the origin of the sea-level highstand during interglacial stage 11

Abstract

Termination (T) 5, ~424 ka, involved the biggest deglaciation of land-ice mass during the Quaternary. Warming and ice-sheet retreat during T5 led to an exceptionally long period of interglacial warmth known as Marine Isotope Stage (MIS) 11, ~424–395 ka. A detailed understanding of the history of continental ice-sheet decay during T5 is required to disentangle regional contributions of ice-sheet retreat to sea-level rise (that range between ~0 and 13 m above present day) and to correct it for glacio-isostatic adjustments (GIA). Yet little is known about the timing and magnitude of retreat during this time of the volumetrically most important continental ice sheet in the Northern Hemisphere, the Laurentide Ice Sheet (LIS). Here we present new authigenic Fe-Mn oxyhydroxide-derived high-resolution records of Pb isotope data and associated rare earth element profiles for samples spanning T5 from Labrador Sea IODP Site U1302/3. These records feature astronomically-paced radiogenic Pb isotope excursions that track increases in chemical weathering of North American bedrock and freshwater routing to the Labrador Sea via Hudson Straits associated with LIS retreat. Our records show that LIS retreat during T5 began 429. 2 ±7.9 ka (2σ) and likely occurred over a longer timescale (by ~10 to 5 kyr) than that observed for T2 and T1. They also show that Hudson Bay Ice Saddle collapse (and therefore LIS break-up) occurred ~419 ±4.7 ka (2σ), around the same time as best estimates of southern Greenland deglaciation, but ~12 kyr before LIS deglaciation and the sea-level high-stand associated with the latter half of MIS 11 likely occurred, ~405 ka. Our findings therefore highlight that ice-mass loss on North America likely played an important role in the seemingly protracted nature of T5 sea-level rise. A comparison of the deglaciation histories of the LIS and the southern Greenland Ice Sheet during T5, T2 and T1 also demonstrates that the well-constrained history of regional ice-sheet retreat during T1 is not always applicable as a template for older late Pleistocene terminations in GIA modelling.