Holocene fluctuations of a polythermal glacier in high-alpine eastern Jotunheimen, central-southern Norway

Bukkehammarbreen is a polythermal cirque glacier lying in the permafrost zone of eastern Jotunheimen, central-southern Norway. In the proglacial lake Bukkehammartjorna, sediment analyses of loss-on-ignition (LOI), magnetic susceptibility and analyses of grain-size distribution have been used to reconstruct Holocene variations in glacier activity and other catchment processes. The glacier has low-sediment production, hence a low signal-to-noise ratio of mincrogenic sediment flux is found. Grain-size analyses are used to enhance the glacigenic signal and to detect glacier variations and other changes in sediment input. The sedimentological record from Bukkehammartjorn is compared with three other lake records from the same region in order to separate the glacial signal from variations in organic production and episodes of enhanced non-glacial minerogenic sedimentation. Subsequent to the deglaciation after the Younger Dryas, a preboreal glacial advance culminated before 10,100cal. BP. This was followed by a prolonged period with no glaciers in the catchment until 7500 cal. BP, after which there is evidence of limited glacier activity lasting until 6800 cal. BP. Between 6700 and 6000 cal. BP the catchment was deglaciated. After 6000 cal. BP Bukkehammarbreen reformed, increasing in size towards similar to3800 cal. BP, with evidence for reduced glacier activity around 5200 cal. BP. A glacier with approximately similar size as at present has existed after similar to3800 cal. BP. The investigation has demonstrated the usefulness of multi-site and multi-parameter lacustrine investigations in reconstructing glacier fluctuations and for testing and validating the results. The investigations have shown that grain-size variations in sediment cores located at increasing distance from the meltwater inlet of a lake may provide an indicator of paraglacial activity in the catchment during the Holocene. The results also suggest that the lower altitudinal limit of permafrost in eastern Jotunheimen remained below about 1800 m during the Holocene. (C) 2004 Published by Elsevier Ltd.