Ice-burial history and early Holocene thinning of the Scandinavian Ice Sheet at Gaustatoppen, southern Norway

This paper explores the glacial history of Gaustatoppen Mountain in southern Norway using cosmogenic nuclide analysis (in situ 14C, 26Al, 10Be, 21Ne) from a vertical transect of surface samples and a shallow (1.3 m) bedrock profile. Analysis of in situ 14C is central to establishing that the entire mountain was buried by the Scandinavian Ice Sheet during the Last Glacial Maximum until rapid thinning (0.4–19 m yr−1) at the end of the Younger Dryas isochrone and/or in the Early Holocene. This implies that ice-sheet thinning coincided with rapid retreat from coastal moraines (c. 190 m yr−1) and suggests that the ice margin retreated faster inland than former ice-sheet reconstructions suggest. We further deduce that the Scandinavian Ice Sheet expanded to bury Gaustatoppen no later than c. 31–36 ka consistent with regional chronologies. Just below the summit, long-lived cosmogenic nuclide ages cluster at c. 70–80 ka, indicating a pre-Last Glacial Maximum erosional event possibly linked to the penultimate glacial maximum. Using Markov Chain Monte Carlo inversion modelling of cosmogenic 10Be and 26Al in a depth profile we constrain the most likely ice burial and erosion history. We find that Gaustatoppen (at 1714 m a.s.l.) was buried by ice for c. 1.3–26.3 % of time since 500 ka, and that the sampled bedrock outcrop eroded c. 2.6–11.8 m within the same period, and with the last 1 m of erosion occurring within the last c. 130–200 kyr. Collectively, these findings provide valuable insights into the dimensions and dynamics of the Scandinavian Ice Sheet during the last glacial period.