Cirque glaciers as morphological evidence for a thin Younger Dryas ice sheet in east-central southern Norway

Three localities with marginal moraines deposited by former cirque glaciers are investigated in east-central southern Norway. The wet-based (erosive) cirque glaciers with aspects towards S-SW and N-NE are mapped at altitudes above 1100 m, and have a mean equilibrium-line altitude of 1275 m. With a suggested mean annual winter precipitation close to the average for the modern accumulation season (1 October-30 April) when the cirque glaciers existed, the mean air-temperature depression during the ablation season (1 May-30 September) is calculated to be 6–7°C lower than at present. The high-altitude cirques of central Rondane were still covered by ice when the low-altitude cirque glaciers developed in distal position for this massif in eastern Rondane and on isolated mountains. Hence, the cirque glaciers are suggested to have existed during the deglaciation after the Late Weichselian maximum, and most likely during the Younger Dryas (11000–10000 BP). The cirque glaciers indicate a downwasting ice-sheet surface well below an altitude of 1100 m prior to the Younger Dryas, and this supports a limited (small) vertical extent for the Late Weichselian ice sheet in this region. With the contemporaneous level for instantaneous glacierization (glaciation threshold) just below the highest elevated peaks in east-central southern Norway, this fits with the idea of a continuous downwasting of the Late Weichselian ice sheet since the 'first' nunataks appeared. The occurrence of the cirque glaciers indicates a multidomed Scandinavian ice-sheet geometry during the Late Weichselian.