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.
The project RAISIN represents a core project of the Focus Area Group PASTSOILS. One of the major goals of the Focus Area Group will be achieved through RAISIN: Rates of soil forming processes in different climates, obtained from soils and paleosols in settings where climatic conditions and duration of soil development are known, will be assessed and documented. Thus, the project will provide a solid base for future interpretation of paleosols in the frame of palaeo-environmental reconstructions. Numerous data on soil development with time, many of them based on soil chronosequence studies in various regions, have been published in the past decades. The main aim of the project is hence to bring together scientists working on rates of soil-forming processes in different regions of the world to share and discuss their results, review and compare published data and finally produce a document representing the current state of knowledge on soil formation rates in different climates. The outcome of the project will be published in a special issue of Quaternary International to make it available to the scientific public. Thus, a common standard for interpreting paleosols in soil-sediment successions in terms of duration and environmental conditions of soil development will be created. Moreover, gaps in our current knowledge will be identified in the process of reviewing existing data in the frame of the project. This will stimulate future research and possibly lead to collaborative projects aiming on closing the identified gaps step by step.