Comment on Was Scotland deglaciated during the Younger Dryas? by Small and Fabel (2016)

The course of climatic events in Scotland and the broader North Atlantic region during the glacial termination has important implications for our understanding of the causes and mechanisms of abrupt climate change but remains in debate. One example is the timing of the late-glacial Loch Lomond Readvance (LLR), during which an ice cap and numerous cirque glaciers were nourished in the Scottish Highlands. Exactly when the LLR occurred and culminated has been disputed for several decades and has been addressed via several different types of chronologic evidence (e.g., Lowe and Walker, 1976; Golledge et al., 2007; MacLeod et al., 2011; Bromley et al., 2014). Recently, Small and Fabel (2016) presented a suite of six 10Be surface-exposure ages from moraine ridges on Rannoch Moor, central Scottish Highlands, that questioned whether two different dating techniques - 10Be and 14C - yield the same result for the timing of final deglaciation of the Scottish ice cap. In that study, Small and Fabel (2016) concluded that the 10Be data show deglaciation occurred at the close of the Younger Dryas (YD) stadial ( #8764;11.6 kyr), as much as a millennium later than the scenario presented by Bromley et al. (2014) based on minimum-limiting 14C data. While the issue of which, if either, is a more reliable age for deglaciation cannot be resolved fully in a short note, we comment on several points raised by Small and Fabel (2016) and suggest a means to resolve this question.