Interpreting exposure ages from ice-cored moraines: a Neoglacial case study on Baffin Island, Arctic Canada

Be-10 dating of moraines has greatly improved our ability to constrain the timing of past glaciations and thus past cold events. However, the spread in ages from a single moraine is often greater than would be expected from measurement uncertainty, making paleoclimatic interpretations equivocal. Here we present 28 new Be-10 ages from ice-cored Neoglacial moraines on Baffin Island, Arctic Canada, and explore the processes at play in moraine formation and evolution through field observations and a numerical debris-covered glacier model. The insulating effect of debris cover modifies glacier lengths and results in the development of ice-cored moraines over multiple advances and thousands of years. Although ice cores can persist for several millennia, spatially variable ice core melt-out contributes to moraine degradation and boulder destabilization, making it likely that the Be-10 clock is reset on moraine boulders in these settings. Thus, exposure ages from ice-cored moraines must be interpreted with caution. The oldest ages, after excluding samples with inheritance, provide the best estimates of initial moraine formation. Three Baffin Island moraines yield Be-10 ages suggesting formation at 5.2, 4.6 and 3.5 ka, respectively, adding to a growing body of evidence for significant summer cooling millennia before the Little Ice Age. Copyright (C) 2017 John Wiley & Sons, Ltd.