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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). [ABSTRACT FROM AUTHOR]

Because global sea level during the last interglacial (LIG; 130-115 ka) was higher than today, the LIG is a useful 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, U-Series dating, K-Ar dating), non-radiometric methods (amino acid dating, luminescence methods, and electron spin resonance, tephrochronology) as well as various stratigraphic and palaeoenvironmental approaches. As the areas in this database were covered by ice sheets from the penultimate glaciation and were affected by glacial isostatic adjustment (GIA), most of the proxies show that sea level was much higher than present during the LIG. Many of the sites show evidence of regression due sea level fall due to GIA uplift, and some also show fluctuations that may reflect regrowth of continental ice or increased influence of the global sea level signal. The database is available at https://doi.org/10.5281/zenodo.5602212 (Dalton et al., 2021). [ABSTRACT FROM AUTHOR]

We report previously unpublished evidence for a Marine Isotope Stage 3 (MIS 3; 60-26 ka) glacial outburst flood in the Torngat Mountains (northern Quebec/Labrador, Canada). We present 10Be cosmogenic exposure ages from legacy fieldwork for a glacial lake shoreline with evidence for outburst flooding in the Torngat Mountains, with a minimum age of 36±3 ka (we consider the most likely age, corrected for burial, to be ~56 ±3 ka). This shoreline position and age can potentially constrain the Laurentide Ice Sheet margin in the Torngat Mountains. This region, considered a site of glacial inception, has no published dated geologic constraints for high-elevation MIS 3 ice margins. We estimate the freshwater flux associated with the inferred glacial outburst flood using high-resolution digital elevation maps corrected for glacial isostatic adjustment. Using assumptions about the ice-dammed locations we find that a freshwater flood volume of 1.14x1012 m³ could have entered the Hudson Strait. This glacial outburst flood volume could have contributed to surface ocean freshening to cause a measurable meltwater signal in δ18O records, but would not necessarily have been associated with substantial ice rafted debris. Future work is required to refine estimates of the size and timing of such a glacial outburst flood. Nevertheless, we outline testable hypotheses about the Laurentide Ice Sheet and glacial outburst floods, including possible implications for Heinrich events and glacial inception in North America, that can be assessed with additional fieldwork and cosmogenic measurements. [ABSTRACT FROM AUTHOR]

Accurately reconstructing the paleogeography of the Laurentide Ice Sheet (LIS) during Marine Isotope Stage 3 (MIS 3; ca. 57,000 to ca. 29,000 yr B.P.) is critical for understanding glacial growth toward the Last Glacial Maximum (LGM), refining sea-level histories, and studying the Earth system response to rapid climate change events. Here, we present a geochronological data set useful for testing hypotheses of global sea level and refining ice sheet configuration through this interval. Data (n = 735) span the entire MIS 3 interval and consist of 14C determinations (n = 651), cosmogenic exposure ages (n = 52), and optically stimulated luminescence dates (n = 32). On that basis, we hypothesize that the central region of the LIS underwent a dramatic reduction in ice from ca. 52 to 40 ka. Key to this hypothesis are geological records at sites in the Hudson Bay Lowlands (east central Canada) that suggest a marine incursion and development of terrestrial landscapes. We show that these landscapes are consistent with recently published glacial isostatic adjustment predictions that include widespread deglaciation of the eastern (Labrador) sector of the LIS with ice buildup over the western (Keewatin) sector at 42 ka. Ice growth from this minimum toward the LGM is likely to have been rapid. The agreement between this data set and modeling predictions prompts the reassessment of key Late Pleistocene records, including Heinrich events, loess deposition in the continental United States, and sedimentological records from the Gulf of Mexico. [ABSTRACT FROM AUTHOR]

We examined late Holocene (ca. 3300 yr BP to present-day) climate variability in the central Northwest Territories (Canadian Subarctic) using a diatom and sedimentological record from Danny’s Lake (63.48ºN, 112.54ºW), located 40 km southwest of the modern-day treeline. High-resolution sampling paired with a robust age model (25 radiocarbon dates) allowed for the examination of both lake hydroecological conditions (30-year intervals; diatoms) and sedimentological changes in the watershed (12-year intervals; grain size records) over the late Holocene. Time series analysis of key lake ecological indicators (diatom species Aulacoseira alpigena, Pseudostaurosira brevistriata and Achnanthidium minutissimum) and sedimentological parameters, reflective of catchment processes (coarse silt fraction), suggests significant intermittent variations in turbidity, pH and light penetration within the lake basin. In the diatom record, we observed discontinuous periodicities in the range of ca. 69, 88–100, 115–132, 141–188, 562, 750 and 900 years (>90% and >95% confidence intervals), whereas the coarse silt fraction was characterized by periodicities in the >901 and <61-year range (>95% confidence interval). Periodicities in the proxy data from the Danny’s Lake sediment core align with changes in total solar irradiance over the past ca. 3300 yr BP and we hypothesize a link to the Suess Cycle, Gleissberg Cycle and Pacific Decadal Oscillation via occasional inland propagation of shifting air masses over the Pacific Ocean. This research represents an important baseline study of the underlying causes of climate variability in the Canadian Subarctic and provides details on the long-term climate variability that has persisted in this region through the past three thousand years. [ABSTRACT FROM AUTHOR]

We examine pollen, macrofossils and sedimentological proxies from the Ridge Site, an 18-m sequence of glacial and non-glacial sediments exposed along the bank of the Ridge River in the southern Hudson Bay Lowlands ( HBL), Canada. As the HBL is located in the previously glaciated region of North America, palaeorecords from this region have important implications for understanding ice-sheet palaeogeography and climate for the late Pleistocene. Two diamicton units were interpreted as subglacial till deposited by a glacier flowing toward the south-southwest (lower diamicton) and west-southwest (upper diamicton), respectively. Confined between these tills is a 6-m non-glacial unit, constrained to Marine Isotope Stage 3 ( MIS 3; c. 57 000 to c. 29 000 a BP) by three radiocarbon dates. Quantitative analyses of the pollen record (dominated by Sphagnum, Cyperaceae, Pinus, Picea, Salix, Alnus and Betula) suggest that average summer temperature (June, July, August) was 14.6±1.51 °C, which is similar to that of the present day at the site. Total annual precipitation was 527±170 mm as compared to 705 mm present-day. The macrofossil record confirmed the local presence of Betula, Salix and conifers. Our results, in combination with other records from the periphery of the Laurentide Ice Sheet, suggest that vast boreal forest-type vegetation, along with a drier interstadial climate, existed in the region during MIS 3. We also compare pollen-derived palaeoclimate reconstructions from the Ridge Site with reconstructions from a previously published site along the Nottaway River, HBL, which was dated to MIS 5a-d ( c. 109 000 to c. 82 000 a BP). This comparison suggests that, with additional data, it may be possible to differentiate MIS 3 and MIS 5 deposits in the HBL on the basis of relative continentality, with MIS 3 characterized by lower total annual precipitation, and MIS 5 by values similar or greater than present-day. [ABSTRACT FROM AUTHOR]

The Laurentide Ice Sheet played a major role in sea level variability, climate and ecosystem dynamics during the Late Pleistocene (~100 ka to ~10 ka). Despite the importance of this ice sheet, its evolution and dynamics through much of the pre-Last Glacial Maximum (pre-LGM; ~24 ka) interval is poorly constrained owing to widespread (but, importantly, incomplete) erosion of the chronostratigraphic record during the LGM advance. Accordingly, we have a relatively poor understanding of the onset of ice sheet growth toward the LGM, along with few insights into the climate system that persisted during times of long-term continental glaciation. To constrain the pre-LGM evolution of the Laurentide Ice Sheet, we focus on information that can be gleaned from portions of the chronostratigraphic record that escaped erosion. We conducted a literature review and identified >800 geochronological determinations from sub-till sites in the glaciated region of Canada. Preservation of these stratigraphic records tends to be clustered in low-lying regions including the Great Lakes, St. Lawrence Lowlands, and Hudson Bay Lowlands. Preserved stratigraphic sequences represent a wide range of pre-LGM environments (e.g. fluvial, peatland, erosional surfaces) and were largely dated to the ~100 to ~24 ka interval using radiocarbon dating, U-Th dating, and optically stimulated luminescence. Given that sample collection took place over the span of several decades by a wide variety of stratigraphic workers, these data span a wide range of uncertainties. Thus, a key component of this work is the quantification of uncertainties in the chronostratigraphic dataset. This work yields series of maps showing the most likely ice sheet extents for each Marine Isotope Stage from MIS 5e to MIS 3. Hypothesized ice extents are compared with available geomorphological records (glacial lineations and striations) and records of sea level. We present these maps as "best guesses" of the ice sheet configuration during pre-LGM times and we expect that they will inform key areas in which to focus future chronostratigraphic efforts. Owing to the interconnectedness of ice sheet with many elements of the Quaternary climate system, these ice sheet constraints will be of interest wide scientific audience, notably to numerical modellers who require empirically-derived ice margins for new iterations of ice sheet and sea level models. [ABSTRACT FROM AUTHOR]