Landscape preservation under ice? In-situ 10Be and 26Al from summit surfaces along Sognefjord, Norway

• Main Authors: Andersen, Jane Lund, Egholm, David Lundbek, Knudsen, Mads Faurschou, Linge, Henriette, Jansen, John D., Olsen, Jesper, Tikhomirov, Dmitry
• Format: Conference Object
• Language: English
• Published: 2016
• Subjects: Arctic; Nesje; Norway; Svalbard; Fennoscandian; Northern Sweden
• Online Access: https://pure.au.dk/portal/en/publications/e2b13c39-6882-4c5c-a9fa-44f3951724b5; http://www.skb.com/publication/2483898/Nordic+workshop.pdf

In-situ cosmogenic nuclides demonstrate existence of landforms preserved under glacial ice in regions such as Northern Sweden (Fabel, 2002), Svalbard (Gjermundsen, 2015) and New England (Bierman, 2015). Elsewhere, the existence of relict landforms is inferred from landscape morphology. Low-relief mountain summits along Sognefjorden in Norway have in the past been used as a base for re-constructing a regional pre-Quaternary surface (Nesje, 1994). The underlying assumption of this approach is that Quaternary surface processes eroded the summits very little, and the reconstructed surface can then be used to determine the total Quaternary bedrock erosion between the summits. However, the amount of Quaternary erosion of these summit flats remains debated (e.g. Steer, 2012) Here, we present an extensive new dataset of in-situ produced cosmogenic 10Be and 26Al in bedrock and boulders from high and flat summits along a 200 km long transect from the coast to the inner parts of Sognefjorden. Our results indicate substantial glacial modification of the summits within the last 50 ka. Close to the coast, at an elevation of around 700 meters, the cosmogenic nuclide signal was reset around the Younger Dryas. Further inland, our results indicate very little cosmogenic nuclide inheritance prior to the last deglaciation. We do not find any signs of exceptional longevity of the low-relief landscape around Sognefjord. In contrast, our results indicate that the low-relief areas were continuously eroded by glacial and periglacial processes in the Quaternary, and that excluding recent erosion of the summits is likely to underestimate total Quaternary erosion. Bierman et al. Cold-based Laurentide ice covered New England’s highest summits during the Last Glacial Maximum. Geology 43(12), 1059-1062, 2015. Fabel et al. Landscape preservation under Fennoscandian ice sheets determined from in situ produced 10 Be and 26 Al. Earth and Planetary Science Letters 201(2), 397-406, 2002. Gjermundsen et al. Minimal erosion of Arctic alpine ...