Late-Holocene and Younger Dryas glaciers in the northern Cairngorm Mountains, Scotland

We present 17 cosmogenic Be-10 ages of glacial deposits in Coire an Lochain (Cairngorm Mountains), which demonstrate that glacial and nival deposits cover a longer timescale than previously recognised. Five ages provide the first evidence of a late-Holocene glacier in the British Isles. A previously unidentified moraine ridge was deposited after c. 2.8 kyr and defines a small slab-like glacier with an equilibrium line altitude (ELA) at c. 1047 m. The late-Holocene glacier was characterised by rapid firnification and a dominance of sliding, enabling the glacier to construct moraine ridges in a relatively short period. Isotopic inheritance means that the glacier may have existed as recently as the Little Ice Age' (LIA) of the 17th or 18th century ad, a view supported by glacier-climate modelling. Nine Be-10 ages confirm a Younger Dryas Stadial (YDS) age for a cirque-floor boulder till, and date the glacier maximum to c. 12.3 kyr when the ELA was at c. 963 m altitude. Both glaciers existed because of enhanced accumulation from wind-blown snow, but the difference in ELA of only c. 84 m belies the YDS-LIA temperature difference of c. 7 degrees C and emphasises the glacioclimatic contrast between the two periods. Three Be-10 ages from till boulders originally deposited in the YDS yield ages <5.5 kyr and indicate snow-avalanche disturbance of older debris since the mid-Holocene, as climate deteriorated towards marginal glaciation.