Mid and Late Holocene climate and environmental history based on lipid biomarkers from Moossee, Switzerland

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The European Alps are highly sensitive to human impact and climate change. At times of global warming, a rapidly changing hydroclimate with heavy rainfall events, severe summer droughts and water scarcity can be observed. This will increase the risk of more frequent floods and forest fires. Robust reconstructions of past climate and environmental dynamics are needed to better understand climate-landscape interactions, and for future projections and risk assessments. While the vegetation history and temperature changes during the Holocene is well understood, multiple studies indicate strong spatio-temporal variability regarding the hydroclimate. Flood records and lake level reconstructions provide valuable information, yet not all ecologically relevant aspects, like evapotranspiration, are covered at high temporal resolution. Moreover, it is not always trivial to disentangle various influences, i.e. temperature and precipitation, but also anthropogenic effects. After all, anthropogenic activity increased a lot with the onset of the Neolithic ~7000 years ago. Over the last few years, several biomarker methods have become available, allowing to reconstruct hydrology and human impact independently. They are increasingly applied world-wide, yet no high-resolution records combining various lipid biomarkers and their compound-specific isotopic composition are available for the Alps and their forelands so far. The aim of this project is to contribute to an improved understanding of the hydroclimate, environmental and human history in the European Alps. Therefore, lipid biomarker methods will be validated and applied for lake sediments from Moossee, Switzerland. Moossee is a key site for paleoenvironmental reconstructions, because archaeological evidence (pile dwellings) documents the presence of humans since the Neolithic. The sediments are varved and extraordinarily well-dated, and we can build on a continuous high-resolution vegetation, geochemical and charcoal record. In detail, we will reconstruct lake water evaporation during the Mid and Late Holocene at high temporal (30 yr) resolution using compound-specific δ2H of aquatic and terrestrial n-alkanes (Objective 2). To ensure robust interpretation, we first analyse modern plants and topsoils for their n-alkane pattern and compound-specific δ2H composition (Objective 1). Moreover, we apply polycyclic aromatic hydrocarbons to reconstruct past fire dynamics and fecal biomarkers (sterols and bile acids) to detect changes in livestock (Objective 3). This complements the existing charcoal and pollen record, because it helps to further investigate anthropogenic influences on paleofires and possibly even cultural advances in context of archeological findings at Moossee. Our multi-lipid biomarker approach is the first of this kind and will provide valuable insights into the climate and human history of the European Alps.