In Section 5.2 we study various aspects of natural climate change and the impact of such changes on the human habitat. A key objective is deciphering in particular decadal-scale climate variability and major climate changes that passed abruptly in time scales perceptible for humans. Therefore, our endeavours concentrate on establishing high resolution proxy data from natural archives with seasonal temporal resolution like varved lake sediments and tree rings. We mainly work on Quaternary time scales, the youngest period in the Earth’s history which is characterized by major climatic fluctuations and periodically advancing ice shields in the Northern Hemisphere. Our special focus is on the transitional periods from cold glacial to warm interglacial climate states and vice versa because these transitions are characterized by strong and short-term climatic fluctuations. For example, the rapid temperature drop and rise at the onset and demise of the Younger Dryas cold phase are ideal natural experiments to decipher the dynamics and mechanisms of strong and abrupt climate change. This will aid a better understanding of thresholds in the climate system. As a matter of course, we are also interested in the driving mechanisms of climate and environment changes in our present warm interglacial period, the Holocene, which we compare in great detail with that of previous interglacials when modern humans were not interfering with natural processes. More specifically, we establish time series of extreme weather events reaching several thousand years back in time to investigate how the frequency of such weather extremes is related to changes in climatic boundary conditions. We use high-resolution sediment records also to study past variations of the magnetic field and the potential effects of these variations on the climate system.
With our research concept we contribute to the overarching goal of the Earth and Environment research field of the Helmholtz Association which is the assessment of fundamental functions of the system Earth and the interactions between societies and nature, thereby creating a sound knowledge base for securing the long-term foundations of human life. This is about understanding the complex changes of Earth and Environment in detail and to better anticipate future developments so that decision-makers in politics and society can be provided with sound scientific recommendations for management planning.
In order to meet our research targets we develop novel climate proxies based on the composition and structure of finely-layered lake deposits (varve micro-facies) and cell structures of wood (wood anatomy) and calibrate our proxy time series through observation of recent processes (monitoring). Our vision is the integration of long climate time-series from geo-archives and instrumental data to evaluate current changes in a comprehensive long-term context.
Since reconstructions of climate, environment and magnetic field changes from natural archives strongly rely on robust time scales, a key aspect of our research is establishing precise chronologies based on varve and tree-ring counting and tephrochronology.
We have the entire chain of cutting-edge technologies for both varved lake sediment and tree ring analyses from sampling to sophisticated lab analyses available. This includes various coring devices, non-destructive scanning techniques, thin section preparation and microscopic analyses, confocal laser lab for wood anatomy analyses, stable isotope labs for sediments and tree rings, sedimentological, geochemical as well as palaeo- and rock magnetic laboratories. In addition, we use high-end monitoring technologies to observe lake sediment formation and tree ring growth. Among our tools are specially developed, precise coring systems that are able to collect up to 100 meter long continuous lake sediment profiles which cover a full climatic cycle from the penultimate interglacial to the present day warm period.
A central aspect of our research concept is the assessment of regional responses to global changes and their variations in time as well as deciphering leads and lags between different regions. The regional foci of our investigations are clustered along various transects across the Eurasian continent. Backbone of the lake sediment research are varved maar lakes in the Eifel (Meerfelder Maar), Italy (Lago Grande di Monticchio) and China (Sihailongwan) because these lakes contain very long, undisturbed sediment profiles and react sensitively to climatic changes due to their small catchments. Key sites for establishing long records of hydro-meteorological extremes are varved lake records in the alpine realm (Mondsee, Austria, and Ammersee, Germany). Within the Helmholtz Virtual Institute ICLEA (Integrated Climate and Landscape Evolution Analyses) we investigate varved lake sediments in the young glacial landscapes of the northern German (Tiefer See) and Polish (Jezioro Czechowskie) lowlands. We further contribute to the Suigetsu Varved Sediment Project (Japan) and to the large-scale ICDP (International Continental Drilling Program) projects Lake El'gygytgyn Drilling Project (Russia) and Dead Sea Deep Drilling Project (DSDDP)(Israel).
At several forest sites in NE-Germany (www.iclea.de) and Central Asia we are applying special field deployable methods that ultimately allow climatic and isotopic signal transfer to be monitored from atmosphere and soil into the wood of tree rings. In conjunction with quantitative wood anatomy and high resolution intra‐annual isotope analyses of tree‐rings we establishing novel transfer functions that can be calibrated and verified with climatological, hydrological, and ecophysiological instrumental data. Thereby, we improve both, the interpretation of paleoclimate proxy data and the understanding of tree responses (adaptation) to climate change. Long multi-parameter records (tree ring widths, cell structures, stable isotopes) from tree rings are currently being developed for the Holocene and late Glacial periods.