Arctic Holocene glacier fluctuations reconstructed from lake sediments at Mitrahalvøya, Spitsbergen

Abstract

The Arctic region has experienced a significantly larger warming during the last decades compared to the rest of the world, and model simulations indicate a continued amplification of future global warming in the Polar Regions. A better understanding of natural climate variability in the Arctic is much needed to provide a better context for the observed warming trend. By utilising proxy data it is possible to obtain palaeoclimatic records beyond the range of instrumental observations, which increase our understanding of long-term Arctic climate change. Here, a continuous record of past changes in Equilibrium-Line Altitude (ELA) has been reconstructed for the alpine glacier Karlbreen, located on the northwest coast of Spitsbergen (79° N), based on sediment analyses from a distal glacier-fed lake. A multivariate statistical analysis suggests that the concentration of geochemical elements Ti, Si and K in the lake sediments, together with the physical parameter dry-bulk-density (DBD), reflect changes in the amount of inorganic detrital input to Kløsa, which is closely linked to the size and ELA of the upstream glacier Karlbreen. A linear regression model based on historically documented glacier extents was used to calculate continuous ELA changes back to ∼3500 cal. yr. BP. From about 9200 to 3500 cal. yr. BP, the sedimentary record indicates that Karlbreen was very small or had completely melted away. Karlbreen was probably close to its maximum Holocene extent several times during the Neoglacial, first around 1700 cal. yr. BP, then later at ∼225 and ∼135 cal. yr. BP. An ice-cored moraine system in front of Karlbreen extends well into the main basin of Kløsa, and it is difficult to explain how this moraine could have formed without disturbing the sedimentary record in the lake (e.g. through slumping events). The sedimentary record in Kløsa is continuous and undisturbed over the past 6700 years, suggesting that the outermost moraine formed prior to this time and that it most likely survived the Holocene Thermal Maximum on Svalbard.