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The North American Ice Sheet Complex (NAISC; consisting of the Laurentide, Cordilleran and Innuitian ice sheets) was the largest ice mass to repeatedly grow and decay in the Northern Hemisphere during the Quaternary. Understanding its pattern of retreat following the Last Glacial Maximum is critical for studying many facets of the Late Quaternary, including ice sheet behaviour, the evolution of Holocene landscapes, sea level, atmospheric circulation, and the peopling of the Americas. Currently, the most up-to-date and authoritative margin chronology for the entire ice sheet complex is featured in two publications (Geological Survey of Canada Open File 1574 [Dyke et al., 2003]; 'Quaternary Glaciations - Extent and Chronology, Part II' [Dyke, 2004]). These often-cited datasets track ice margin recession in 36 time slices spanning 18 ka to 1 ka (all ages in uncalibrated radiocarbon years) using a combination of geomorphology, stratigraphy and radiocarbon dating. However, by virtue of being over 15 years old, the ice margin chronology requires updating to reflect new work and important revisions. This paper updates the aforementioned 36 ice margin maps to reflect new data from regional studies. We also update the original radiocarbon dataset from the 2003/2004 papers with 1541 new ages to reflect work up to and including 2018. A major revision is made to the 18 ka ice margin, where Banks and Eglinton islands (once considered to be glacial refugia) are now shown to be fully glaciated. Our updated 18 ka ice sheet increased in areal extent from 17.81 to 18.37 million km(2), which is an increase of 3.1% in spatial coverage of the NAISC at that time. Elsewhere, we also summarize, region-by-region, significant changes to the deglaciation sequence. This paper integrates new information provided by regional experts and radiocarbon data into the deglaciation sequence while maintaining consistency with the original ice margin positions of Dyke et al. (2003) and Dyke (2004) where new information is lacking; this is a pragmatic solution to satisfy the needs of a Quaternary research community that requires up-to-date knowledge of the pattern of ice margin recession of what was once the world's largest ice mass. The 36 updated isochrones are available in PDF and shapefile format, together with a spreadsheet of the expanded radiocarbon dataset (n = 5195 ages) and estimates of uncertainty for each interval. (C) 2020 Elsevier Ltd. All rights reserved.

Annual shoot length of the circumarctic dwarf shrub Cassiope tetragona has proved to be a reliable proxy for past and ongoing climate change in the Arctic. This is based on its strong linear relationship with monthly climate parameters. Monthly means are, however, coarse units for prediction of growth in marginal regions with short growing seasons. An alternative to monthly averages are parameters that quantify the growing season length (GSL) and its intensity (growing degree-days; GDD5). GDD5 is defined as the cumulative daily mean temperature above 5°C. GSL is defined as the number of days on which the average temperature exceeds 5°C. The aims of this study were to test whether these parameters are a better predictor of growth than monthly means and to reconstruct past High Arctic growing season climate. Correlative analysis shows that GDD5 is a better predictor of annual shoot length growth than mean monthly temperatures and GSL, both at C. tetragona’s European northern and southern distribution limit, as well as at its assumed climatic optimum. Svalbard Airport GDD5 was reconstructed back to 1857. The reconstruction shares 61% of variance with the instrumental record. This opens the possibility to obtain an Arctic network of climate reconstructions with high temporal and spatial resolution through construction of C. tetragona shoot length chronologies.

Stable isotope records are increasingly being used in palaeoenvironmental studies of Arctic lakes. Here we compare stable isotope and elemental records (delta C-13, delta N-15 C/N) with high resolution XRF-derived geochemical and colour data from low Arctic lakes (SS1220 and SS85) in southwest Greenland. Lake SS1220 sediments are laminated gyttja whereas SS85 consist of homogeneous gyttja, both records cover the last c. 5000 years. delta C-13 and carbon content suggest that organic matter in both lakes is predominantly autochthonous. The C/N variability, ranging between 11 and 15, is interpreted to be a function of nitrogen deficiency which is further supported by delta N-15 values (at SS1220) falling close to atmospheric delta N-15(atmosphere). Although some changes in the geochemical stratigraphies presented here can be related to regional environmental change (i.e. hydrology, effective precipitation, aeolian activity), these effects are filtered through the lake catchments. These changes alter the nutrient supply and hence lake productivity which appear to be the primary controls on the stable isotope data. We suggest that information of past environmental change can only be gained from the stable isotope composition of lake sediments when there is a reasonable understanding of limnological processes, and records may be lake specific. (C) 2012 Elsevier Ltd. All rights reserved.