The 11.8 m-long composite sediment record from the hardwater lake of Sacrower See, located near the city of Potsdam (north-eastern Germany), has been characterised by a range of analytical techniques. These include magnetic susceptibility, chemical parameters (XRF core scanning, CNS analysis, biogenic silica) and stable isotopes (13C, 15N). The chronology covers the entire Holocene and the concluding Lateglacial (Alleröd, Younger Dryas) and is based on age-depth modelling using radiocarbon dates refined by the onset of the local varve chronology in 1870 CE (Lüder et al., 2006) and by the Laacher See Tephra, an isochrone dated to 13,000 cal. BP. It offers a detailed environmental reconstruction providing insights into depositional processes influenced by both natural climatic variations and human activities (Enters et al., 2009; Kirilova et al., 2009). The Lateglacial and Early Holocene are distinguished by the stabilisation of natural landscapes characterised by the presence of pine-birch (Alleröd) and mixed oak forests (Early Holocene). This development was interrupted by the climatic deterioration of the Younger Dryas, which resulted in a destabilisation of vegetation and increased natural soil erosion. It is evident that, for the first time around 5500 cal. BP, anthropogenic forest clearing became a factor, which subsequently led to increasing cultural soil erosion further accelerating during the Bronze Age (3600-3200 cal. BP), the Early Iron Age (2800-2600 cal. BP) and the Middle Ages (900-600 cal. BP). In the course of industrialisation since the 19th century, human impact underwent a transition from the destabilisation of soils to the phenomenon of eutrophication. This transition resulted in the occurrence of hypolimnetic anoxia, accompanied by the formation of carbonaceous varves.
Lacustrine environmental archives with annually laminated (varved) sediments permit a calendar-year chronology and allow calculation of precise sediment accumulation rates. We present multiproxy analyses of a varved sediment record from Holzmaar (West-Eifel Volcanic Field, Germany) for the last 16,000 years providing a continuous diatom stratigraphy supported by physical and chemical parameters with a centennial resolution. Patterns of diatom assemblages infer the trophic history of Holzmaar. There is a distinct variation at the Pleistocene/Lateglacial transition characterized by a replacement of Staurosira construens with Stephanodiscus minutulus, increases of Ca/Ti, TOC/TN ratios and biogenic silica, together suggesting an increase in lacustrine productivity and a shift of the lake's trophic status from oligotrophic to mesotrophic. These conditions remain during the Bölling/Alleröd interstadial. During the Younger Dryas stadial, there is a decrease on organic productivity as reflected by TOC, a subtle increase on benthic and epiphytic diatoms, indicating colder and dry conditions, and S. minutulus remains dominant suggesting increased winds. The Postglacial is dominated by Lindavia radiosa, S. minutulus and Nitzschia paleacea. The latter occurs between 9000-6000 cal yr BP together with an increase of TOC/TN and TS suggesting eutrophication with periodic anoxia during the Holocene Thermal Maximum. After 2200 cal yr BP, L. radiosa and Pantocsekiella comensis are dominant suggesting warmer conditions (especially during the Medieval Climate Anomaly) and thermal stability. Increased surface runoff is reflected in higher values of Ti and MS, suggesting more humidity and enhanced by anthropogenic disturbance. Moreover, the appearance of Aulacoseira subarctica is related to a cold and wet period coinciding with the Little Ice Age. In addition to environmental changes, our multiproxy analyses track human impact since the Middle Neolithic.
Humans impact fire regimes by changing fire ignition, fuels, and land cover. Although fire regimes dramatically alter interactions between the land surface, biosphere, and atmosphere, the impact of these fires on the climate system is not clear. Biomass burning caused by current human activities emits carbon dioxide equal to 50Prozent of the emissions from fossil-fuel combustion and is therefore highly likely to influence future climate change. The multi-proxy nature of ice and lake cores presents ideal material to investigate the links between biomass burning and climate change. The primary objective of the project is to study temporal and regional evolution of biomass burning during the Holocene in Central and North America to determine anthropogenic fire impacts on the climate system with the advent of agriculture and in a warming climate. This requires high-resolution biomass burning proxy records combined with Holocene climate records at the respective locations. The approach is based on analyses of levoglucosan, an excellent proxy for past biomass burning, on Central and North American lake sediment cores as well as on the Greenland NEEM deep ice core and their interpretation in context with climate records. The Department of Environmental Sciences, Informatics, and Statistics of the University of Venice is particularly suited to host this project as it is one of the worldwide leading groups in quantitative investigations of the early impact of humans on the climate system by analyzing past fires recorded in ice and sediment cores.