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

Abstract

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.

Holocene palaeoclimate reconstructions at Vanndalsvatnet, western Norway, with particular reference to the 8200 cal. yr BP event

“…When the two parameters are positively correlated and in phase, the minerogenic sediments are most likely deposited from suspension in a low-energy environment. Sorting/mean anomalies (when the two parameters are in anti-phase/negatively correlated), on the other hand, most likely mean that the sediments are deposited in a high-energy environment (eg, during a river flood/colluvial episode) (eg, Bakke et al, 2005b). As seen from the upper panel in Figure 6, the two parameters are in phase …”

Simulating the evolution of Hardangerjøkulen ice cap in southern Norway since the mid-Holocene and its sensitivity to climate change

“…Reconstructions show that glaciers in southern Norway did not survive the mid-Holocene thermal maximum (e.g., Bakke et al, 2005;Nesje, 2009). Based on lake sediments and terrestrial deposits, Hardangerjøkulen is estimated to have been absent from ca.…”

“…To extract a climate signal, linear assumptions between ice extent (area), ice volume (mass balance), climate and their geomorphological or proxy signal are commonly assumed in glacier reconstructions (e.g., Liestøl in Sissons, 1979;Bakke et al, 2005). Linearity is also commonly assumed in simplified models used to extract climate information from glacier variations (e.g., Harrison et al, 2001;Oerlemans, 2005;Lüthi, 2009;Roe, 2011).…”

Changes in atmospheric variability in a glacial climate and the impacts on proxy data: a model intercomparison

“…Allen et al, 1999;Bakke et al, 2005;Bahr et al, 2006). Unfortunately, the same geographic site may record a qualitatively different mixture of mean and variance contributions in different climates.…”