Glacier fluctuations, equilibrium-line altitudes and palaeoclimate in Lyngen, northern Norway, during the Lateglacial and Holocene

Abstract

Based on lacustrine and morpho-stratigraphical evidence from Lyngen in Troms, northern Norway, 13 marginal moraines have been mapped in front of Lenangsbreene in Strupskardet. Moraines M1-M13 are inferred to represent glacier halts or advance/readvance taking place during the Lateglacial and Holocene. The presence of collapse depressions suggests that some of them were ice cored (M1-M3). A chronological framework, taking into account a combination of former shorelines and related glacier-meltwater channels, lichenometry and AMS radiocarbon-dated lacustrine sediments spanning the last 20 000 cal. yr BP, has been established. The distal glacier-fed lake Aspvatnet was isolated from the sea c 10 300 cal. yr BP, and the lacustrine sediments have been investigated by use of loss-on-ignition (LOI) magnetic susceptibility, water content, wet and dry bulk density (DBD), and the magnetic parameters anhysteretic remanent magnetization (ARM) and saturation remanent magnetization (SIRM). There is, in general, good agreement between physical sediment parameters and magnetic parameters. DBD, a combination of medium and fine silt and the two statistical parameters ‘sorting’ and ‘mean’ have been used to construct a high-resolution glacier-fluctuation curve for the last 3800 cal. yr BP. Based on an accumulation-area ratio (AAR) of 0.6 and an ablation-accumulation balance ratio (ABR) approach, a continuous temperature-precipitation-wind equilibrium-line altitude (TPW-ELA) curve for the last 20000 cal. yr BP has been constructed. Using an established exponential relationship between mean ablation-season temperature and mean annual solid precipitation at the ELA of Norwegian glaciers, variations in mean winter precipitation (snow) are quantified using an independent proxy for summer temperature. Mean annual winter precipitation varied from 500 to 5000 mm water equivalent, and on average, Holocene estimates are c. 50% higher than similar figures from the Lateglacial. The two driest periods occurred during Heinrich events 1 (HI) (17 500-16 500) and 0 (HO) (13 000-12 200), whereas freshwater pulses to the North Atlantic had apparently no systematic impact on mean winter precipitation. Based on the winter precipitation curve from Lyngen, the atmospheric circulation responded to the sea surface temperature (SST) lowering associated with HI and HO. The dry and cold climate during the events led to formation of talus-derived rock glaciers at sea level.