The Goldilocks dilemma: big ice, little ice, or “just-right” ice in the Eastern Canadian Arctic

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Our conceptions of the NE sector of the Laurentide Ice Sheet (LIS) at the Last Glacial Maximum (LGM) have evolved through three major paradigms over the past 50 years. Until the late 1960s the conventional view was that the Eastern Canadian Arctic preserved only a simple deglacial sequence from a LIS margin everywhere at the continental shelf edge (Flint Paradigm). Glacial geologic field studies began in earnest in this region in the early 1960s, and within the first decade field evidence documenting undisturbed deposits predating the LGM led a pendulum swing to a consensus view that large coastal stretches of the Eastern Canadian Arctic remained free of actively eroding glacial ice at the LGM, and that the most extensive ice margins occurred early in the last glacial cycle. This Minimalist Paradigm dominated until the late1980s when an expanded data set from shallow marine studies indicated LGM ice at least locally reached the continental shelf. Within the past decade the marine data, coupled with new evidence from lake sediments and cosmogenic exposure dates on moraines and glaciated terrain in the Eastern Canadian Arctic has led to a new paradigm that better reconciles the terrestrial and marine evidence. Collectively, these lines of evidence indicate that all of southern Baffin Island was glaciated at the LGM, but that some coastal uplands north of Cumberland Sound remained above the limit of actively eroding glacial ice, even though outlet glaciers reached the continental shelf in front of most fiords and sounds. The most plausible explanation for the observed glacial limits is that low-gradient, relatively fast-moving outlet glaciers sliding on deformable sediments occupied marine embayments and fiords, contrasting with slower moving ice frozen to its bed on the intervening crystalline terrain. Slow-moving ice frozen to its bed would have had steeper surface gradients, hence would have terminated inland from the coast. This scenario is consistent with observations indicating high-elevation coastal terrain remained unglaciated even though outlet glaciers reached the continental shelf. LGM summer temperatures were apparently much lower than present, as lakes in the ice-free regions were permanently frozen.