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Because global sea level during the last interglacial (LIG; 130–115 ka) was higher than today, the LIG is a useful approximate analogue for improving predictions of future sea-level rise. Here, we synthesize sea-level proxies for the LIG in the glaciated Northern Hemisphere for inclusion in the World Atlas of Last Interglacial Shorelines (WALIS) database. We describe 82 sites from Russia, northern Europe, Greenland and North America from a variety of settings, including boreholes, riverbank exposures and along coastal cliffs. Marine sediments at these sites were constrained to the LIG using a variety of radiometric methods (radiocarbon, uranium–thorium, potassium–argon), non-radiometric methods (amino acid dating, luminescence methods, electron spin resonance, tephrochronology) as well as various stratigraphic and palaeo-environmental approaches. In general, the sites reported in this paper do not offer constraint on the global LIG highstand, but rather evidence of glacial isostatic adjustment (GIA)-influenced sea-level positions following the Marine Isotope Stage 6 glaciation (MIS 6; 191–130 ka). Most of the proxies suggest that sea level was much higher during the LIG than at the present time. Moreover, many of the sites show evidence of regression due to sea-level fall (owing to glacial isostatic uplift), and some also show fluctuations that may reflect regrowth of continental ice or increased influence of the global sea-level signal. In addition to documenting LIG sea-level sites in a large swath of the Northern Hemisphere, this compilation is highly relevant for reconstructing the size of MIS 6 ice sheets through GIA modelling. The database is available at https://doi.org/10.5281/zenodo.5602212 (Dalton et al., 2021).

The North American Ice Sheet Complex (comprising the Laurentide, Cordilleran and Innuitian ice sheets) was the largest ice mass in the Northern Hemisphere that grew towards and waned after the Last Glacial Maximum. The existing ice margin chronology available for the North American Ice Sheet Complex is based on radiocarbon data only and does not reflect other geochronometric information constraining the last deglaciation, such as cosmogenic exposure- or optically stimulated luminescence ages. Here we present a series of newly produced ice margin isochrones from 25 ka to present, in a time step of 500 years. For each isochron, we draw maximum, best estimate, and minimum ice margin position in an attempt to capture the existing uncertainty. The ice margin isochrones are based on (i) an up-to-date dataset of radiocarbon ages (~5000), (ii) 10Be and 26Al cosmogenic nuclide data that directly date ~80 ice-marginal features over North America, (iii) ~350 optically stimulated luminescence ages dating the deposition of an aeolian cover immediately post-deglaciation, (iv) the ice-sheet scale glacial geomorphology record. Our effort brings the information on the last North American Ice Sheet Complex deglaciation on par with that for the Eurasian Ice Sheets and should serve the broad community of Quaternary research from archaeology to numerical ice sheet modelling.

The Laurentide Ice Sheet was the largest global ice mass to grow and decay during the last glacial cycle (~115 ka to ~10 ka). Despite its importance for driving major changes in global mean sea level, long-term landscape evolution, and atmospheric circulation patterns, the history of the Laurentide (and neighbouring Innuitian) Ice Sheet is poorly constrained owing to sporadic preservation of stratigraphic records prior to the Last Glacial Maximum (LGM; ~25 ka) and a case-study approach to the dating of available evidence. Here, we synthesize available geochronological data from the glaciated region, together with published stratigraphic and geomorphological data, as well as numerical modelling output, to derive 19 hypothesised reconstructions of the Laurentide and Innuitian ice sheets from 115 ka to 25 ka at 5-kyr intervals, with uncertainties quantified to include best, minimum, and maximum ice extent estimates at each time-step. Our work suggests that, between 115 ka and 25 ka, some areas of North America experienced multiple cycles of rapid ice sheet growth and decay, while others remained largely ice-free, and others were continuously glaciated. Key findings include: (i) the growth and recession of the Laurentide Ice Sheet from 115 ka through 80 ka; (ii) significant build-up of ice to almost LGM extent at ~60 ka; (iii) a potentially dramatic reduction in North American ice at ~45 ka; (iv) a rapid expansion of the Labrador Dome at ~38 ka; and (v) gradual growth toward the LGM starting at ~35 ka. Some reconstructions are only loosely constrained and are therefore speculative (especially prior to 45 ka). Nevertheless, this work represents our most up-to-date understanding of the build-up of the Laurentide and Innuitian ice sheets during the last glacial cycle to the LGM based on the available evidence. We consider these ice configurations as a series of testable hypotheses for future work to address and refine. These results are important for use across a range of disciplines including ice sheet modelling, palaeoclimatology and archaeology and are available digitally.