Non-biting midges (Chironomidae) as a proxy for summer temperatures during the post-Holsteinian (MIS 11b) – a central European perspective

Abstract. Climatic and environmental changes during past interglacial periods can be investigated to improve our understanding of mechanisms governing the changes which are currently observed. Numerous proxies might be utilised to reconstruct various environmental parameters. For instance, pollen analysis indicates changes in vegetation as well as winter temperature fluctuations, while Chironomidae larvae head capsules are widely used to recreate summer thermal conditions. Non-biting midges remains indicate trophy and pH of water bodies as well. Nevertheless, they have been used mostly in the studies of the Holocene with hardly any Chironomid-inferred temperature reconstructions conducted for MIS 11 period. In this study we present the first quantitative summer temperature reconstruction for the post-Holsteinian (Marine Isotope Stage – MIS 11b) in Central Europe based on the analysis of fossil chironomid remains preserved in palaeolake sediments recovered at Krępa, southeastern Poland. The stratigraphic context for the chironomid-based summer temperature reconstruction is provided by pollen data, together allowing to compare our results in the context of climate development at the end of the Holsteinian Interglacial. Chironomidae assemblages at the Krępa site consist mainly of oligotrophic and mesotrophic species (e.g Corynocera ambigua-type, Chironomus anthracinus-type) with lower abundance of eutrophic species (e.g. Chironomus plumosus-type). The chironomid-based summer temperature reconstruction indicates July temperature ranging between 15,3 ॰C and 20,1 ॰C during the early post-Holsteinian. Temperature changes during the first stadial after the Holstein Interglacial period are also reflected by the pollen data, which, however, show a certain delay compared to the chironomids. In any case, results from Krępa prove that conducting Chironomidae analysis is even feasible for periods as early as the mid-Pleistocene, enhancing our understanding of the mechanisms that control present-day climatic and environmental changes. The additional element of this research is indicating sites within the Polish borders that were investigated so far – mostly on the basis of pollen analysis, occasionally Cladocera, isotopes, etc. – and might be new objects of studies based on Chironomid-inferred temperature reconstructions. However, bringing Chironomid analysis with particular emphasis of challenges of conducting it with the use of sediments older than Holocene is the primary aim of this publication. Data from the MIS 11 complex are unique. There are only 4 sites with pre-Late Glacial chironomid-based summer temperature reconstructions in Europe.