Timing of glacier response to Younger Dryas climatic cooling in Scotland

Much speculation surrounds the \textquoteleftYounger Dryas\textquoteright (YD) event, a cold interval with abrupt thermal transitions that, on evidence from Greenland ice cores, lasted from 12.85 until 11.65 ka cal BP (GS-1: Greenland Stadial 1). Stratigraphic records for this interval are often well resolved and fall within the range of a number of dating methods, yet its cause, propagation and regional environmental effects remain unclear. In Scotland this climatic downturn led to a readvance of glacial ice, the precise timing of which has proved difficult to determine. Here we present new varve and radiocarbon evidence that indicates that the last glacier to occupy the Loch Lomond area, the type locality for the YD in Scotland, achieved its maximum extent very late in the YD, after c. 12.0 ka cal BP. This accords with evidence obtained for another former major glacial system in the Scottish Highlands, in the Lochaber area, and with the maximum advance of some large YD ice masses in Norway. The new empirical data from Scotland provide robust chronological constraints for validating numerical simulations of ice growth during the YD, and for assessing the links between climate change and glacier response.