Calibration study for the reconstruction of quantitative climate information from stable oxygen isotope compositions of fossil gastropod shells

• Applicant: Dr. Christiane Richter
• Subject Area: Physical Geography
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 491505649

Given the progressive impact of climate change on our environment, there is a growing demand for reliable climate forecasts and effective climate strategies. For these, robust data bases are essential, which are derived to a large extent from palaeoarchives, such as inland ice or marine sediment cores. However, there are significant data gaps, especially for terrestrial ecosystems. In order to close this gaps, long-term archives such as loess sequences are particularly important. Especially, gastropod communities frequently preserved in these loess sequences are excellent indicators of qualitative environmental information. Additionally, stable oxygen isotope compositions of the shells (δ18O_shell) have the potential to indicate quantitative environmental information. However, this would require calibration studies to obtain appropriately reliable data. The aim of the proposed project is to carry out such calibration studies for some of the most common gastropod species in Eurasian loess archives. The focus is on factors not yet fully understood at the current state of knowledge, e.g., the influence of δ18O of the ingested food water as well as relative humidity on δ18O_shell and the species-specific fractionation between δ18O of the imbibed precipitation (δ18O_precipitation) and δ18O_shell. Further focus is on the verification of the identified relationships for cold arid climate conditions.The calibration studies are to be carried out using laboratory experiments that allow specific parameters to be varied while keeping the other variables constant. If possible, suitable equations shall be developed to reliably calculate δ18O_precipitation from δ18O_shell for each gastropod species. Complementary, the relationship between δ18O_shell of the target species and δ18O_precipitation under natural cold-arid conditions will be tested based on xeromontane ecosystems of the Altay Mountains. This includes the investigation and quantification of potential further environmental influences (such as the uptake of recycled water, evaporation and relative humidity and their effect on the imbibed water and therewith on the gastropod shells), as well as the evaluation of the results/equations from the laboratory investigations under natural conditions. The results could allow the indirect derivation of δ18O_precipitation from fossil gastropod shells most common in loess archives. δ18O_precipitation, in turn, enables us to model quantitative climate data such as air temperatures and atmospheric circulation patterns providing the data basis for e. g. climate impact research and political decision-makers.

• DFG Programme: Research Grants