The potential of non-alpine lakes for quantitative palaeotemperature reconstructions based on subfossil chironomids: A comparative palaeolimnological study from southern Norway

In this study, Holocene mean July temperatures were reconstructed quantitatively based on subfossil chironomid remains. The specific goal was to evaluate whether lakes located below the modern tree line are appropriate sites for the chironomid-based reconstruction of small-scale temperature variations. On this account, the main questions were whether the water chemistry and physical conditions of the chosen lakes can be regarded as stable during the Holocene and whether the chironomid assemblages react sensitively to Holocene temperature fluctuations. To answer these questions, the sediments of the lakes Reiarsdalsvatnet and Isbenttjà ¸nn situated in Setesdal in southern Norway were studied in a multi-proxy approach, including age-depth modelling based on radiocarbon dating, chironomid and pollen analyses, and the analyses of carbon, nitrogen, sulphur and biogenic silica.The results show that subfossil chironomids from the studied non-alpine lakes do react sensitive to small-scale summer temperature fluctuations but they also point to the importance of a cautious selection of study sites. A thorough knowledge about the catchment-lake system and a thorough evaluation of the reconstructed temperatures is crucial to obtain reliable results. The results suggest that non-alpine lakes are high potential sites for the reconstruction of small-scale temperature variations based on chironomids.