Stable isotope analyses
The stable isotope analyses for DecLakes will be provided by one laboratory (LLK-Germany). LLK-Germany can look back to 15 years of successful collaboration with the project leader, including all steps to build up the scientific basis justifying the use of deep-lake ostracod valves from selected lakes as a reliable archive of past d18OP. The concentration of suitable ostracod shells in the sediment is generally low, which means that at the high resolution required for this project only small amounts of carbonate are available for isotopic analysis. A challenge to isotope analysis also arises from the resulting broad range of sample weights, depending on species and ontogenetic state of the carapace, and in particular from low weight samples less than 10 µg carbonate weight. The mass spectrometers of the Leibniz-Laboratory have been customized for the measurement of large numbers of small carbonate samples with the development of the Kiel Device and the long-matured software controlling it. Along with an expert maintenance and supervision of the instruments this allows us to effectively process the series of ca. 12 000 samples deemed necessary for this project. Analyses down to about 6 µg of carbonate are possible. Analytical precision is about 0.03 to 0.05 ‰ on the d18O scale (1s) for weights greater than 10 µg and decreases to about 0.08 ‰ towards the low weight end. Sample weight (as carbonate) will be available from the mass spectrometer signal and along with the taxonomical signature will provide information on the ecological/environmental conditions in the deep habitat of the species.