A successful research strategy has to rely on multi-site and multi-proxy evidence which is achieved for PROSIMUL II through close co-operations with colleagues from other institutions. Within this network PROSMUIL II exploits the dependence of stable isotopes ratios in natural materials on physical and biological processes to study factors influencing lake ecosystems.
The focus is set on stable isotope ratios imprinted into organic carbon, organic oxygen and total nitrogen of sedimentary matter as well as into carbon and oxygen of bio-minerals, especially ostracods and diatoms also be found in the sediments. Through continuous sampling of sediment profiles a basis will be provided for high resolution investigations on isotope chronologies and subsequent time series analysis. As an illustration, generalized pathways of information transfer (physical and biological) in a typical maar lake are shown with respect to the generation of carbon isotope signals of organic matter (Figures 1 and 2).
For this proxy parameters transfer functions have to be developed to translate the encrypted information in the lake sediments into processable figures. Since pure empiric evidence and statistic relations seem to be not sufficient to complete this task in the case of lacustrine sediments, sophisticated deterministic models of signal generation are needed. These have to combine quantities describing different parts of the ecosystem, like sediment accumulation rates, productivity or phytoplankton community, with well known quality of evidence.
Time series analyses will be used to search for stable cyclicities in time. However, since our data mainly can not provide yearly resolution and are furthermore transformed in a non linear way in the ecosystem adapted methods have to be used for analysis. Modelling approaches within PROSIMUL II will be simple ones and are used to falsify a priori hypothesis and achieved reconstructions for single quantities like temperature and precipitation.
