Abstract
Abstract. We present new 10Be surface exposure ages from two selected locations in southern Norway. A total of five 10Be samples allow a first assessment of local deglaciation dynamics of the Scandinavian Ice Sheet at Dalsnibba (1476 m a.s.l.) in southwestern Norway. The bedrock ages from the summit of Dalsnibba range from 13.3±0.6 to 12.7±0.5 ka and probably indicate the onset of deglaciation as a glacially transported boulder age (16.5±0.6 ka) from the same elevation likely shows inheritance. These ages indicate initial deglaciation commencing at the end of the Bølling–Allerød interstadial (∼ 14.7–12.9 kyr BP) and ice-free conditions at Dalsnibba's summit during the Younger Dryas. Bedrock samples at lower elevations imply vertical ice surface lowering down to 1334 m a.s.l. at 10.3±0.5 ka and a longer overall period of downwasting than previously assumed. Two further 10Be samples add to the existing chronology at Blåhø (1617 m a.s.l.) in south-central Norway. The 10Be erratic boulder sample on the summit of Blåhø sample yields 20.9±0.8 ka, whereas a 10Be age of 46.4±1.7 ka for exposed summit bedrock predates the Late Weichselian Maximum. This anomalously old bedrock age infers inherited cosmogenic nuclide concentrations and suggests low erosive cold-based ice cover during the Last Glacial Maximum. However, due to possible effects of cryoturbation and frost heave processes affecting the erratic boulder age and insufficient numbers of 10Be samples, the glaciation history on Blåhø cannot conclusively be resolved. Comparing the different timing of deglaciation at both locations in a rather short west–east distance demonstrates the complex dynamics of deglaciation in relation to other areas in southern Norway.
Highlights
The growth and decay of Quaternary glaciers and ice sheets has had fundamental implications for environmental changes worldwide (Ehlers and Gibbard, 2007)
The cosmogenic exposure ages calculated for all samples from Dalsnibba and Blåhø are shown in Fig. 2 and Table 1
In this paper we present seven in situ cosmogenic 10Be surface exposure ages from two selected mountain locations in southern Norway
Summary
The growth and decay of Quaternary glaciers and ice sheets has had fundamental implications for environmental changes worldwide (Ehlers and Gibbard, 2007). The interpretation of bedrock with different degree of weathering in mountain areas affected by Quaternary glaciation can, be important for determining ice-sheet behaviour and thickness during the last glaciation periods (Brook et al, 1996; Briner et al, 2006; McCarroll, 2016). The two most discussed scenarios suggest on the one hand the preservation of highly weathered uplands by a cover of non-erosive cold-based ice; the trimline would reflect an englacial thermal boundary. The alternative explanation suggests that the trimline represents the true upper vertical ice surface and erosional limit of a former warm-based ice sheet with ice-free nunatak areas above that boundary (Stroeven et al, 2002)
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