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Utilizing physical sediment variability in glacier-fed lakes for continuous glacier reconstructions during the Holocene, northern Folgefonna, western Norway

Bjerknes Centre for Climate Research, Allegt, 55, N-5007 Bergen, Norway; Department of Geography, University of Bergen, Breiviksveien 40, N-5045 Bergen, Norway jostein.bakke{at}geog.uib.no

øyvind Lie

Bjerknes Centre for Climate Research, Allegt, 55, N-5007 Bergen, Norway

Atle Nesje

Bjerknes Centre for Climate Research, Allégt, 55, N-5007 Bergen, Norway; Department of Earth Science, University of Bergen, Allégt, 41, N-5007 Bergen, Norway

Svein Olaf Dahl

Bjerknes Centre for Climate Research, Allégt, 55, N-5007 Bergen, Norway; Department of Geography, University of Bergen, Breiviksveien 40, N-5045 Bergen, Norway

øyvind Paasche

Bjerknes Centre for Climate Research, Allégt, 55, N-5007 Bergen, Norway; Department of Earth Science, University of Bergen, Allégt, 41, N-5007 Bergen, Norway

The maritime plateau glacier of northern Folgefonna in western Norway has a short (subdecadal) response time to climatic shifts, and is therefore well suited for reconstructing high-resolution glacier fluctuations. The reconstruction presented here is based on physical parameters of glaciolacustrine sediments retrieved from two glacier-fed lakes and a peat bog north of the ice cap. Bulk density and modelled glacier net mass balance for the last 200 years show a remarkably similar pattern, where maximum sediment yield lags the glacier net mass balance by-10 years. The record of glacier variations has been transferred into an equilibrium-line altitude (ELA) variation curve. Glaciers respond primarily to changes in summer temperature and winter precipitation. At present there is a high correlation between the North Atlantic Oscillation (NAO) index and measured (since the early 1960s) net mass balance on maritime glaciers in western Norway (r=-0.8). Reconstructed glacier variations from maritime western Norway are therefore considered indicative of the strength of the westerly airflow associated with NAO during the Holocene. The early phase of mid-Holocene glacier growth (5200 cal. yr BP) was characterized by gradual glacier expansion culminating in the first Subatlantic glacial event at 2300 cal. yr BP The climate during the last 2200 years has favoured increased glacier activity at Folgefonna. High-amplitude shifts in ELA may be explained by unstable modes of the westerlies causing significant variability of winter precipitation. During the last 2000 years, Folgefonna expanded and decayed with significant decadal variability. During the latest period of the‘Mediaeval Warm Epoch’, Folgefonna advanced. The Neoglacial maximum, however, was reached during the‘Little Ice Age’ at AD 1750 and AD 1870. The northern Folgefonna glacial record is compared to other Holocene glacier records in Scandinavia.

Key Words: Glacier fluctuations • North Atlantic Oscillation (NAO) • lake sediments • bulk density • ELA reconstructions • Folgefonna • glacier mass balance • Holocene • Norway

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