Advancing climate reconstruction with landsnail shell isotopy: Enhancing temporal resolution and quantitative model accuracy through sclerochronology

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

Palaeoclimatic indicators in geological deposits are a crucial foundation for reconstructing past climate changes and improving our Earth system models. In this context, landsnail shell isotopy represents a promising proxy, especially for terrestrial regions in the mid-latitudes where data is often scarce. Previous studies have demonstrated the potential of reconstructing precipitation isotope signals from the isotopic composition of landsnail shells, thereby complementing data from ice cores, marine foraminifera, and speleothems. Despite current research, it remains challenging to reconstruct precise and robust quantitative data from the isotopic composition of landsnail shells due to various influencing factors. In my current DFG project, I have made significant progress in this area through a comprehensive field study in Central Asia and detailed laboratory experiments. I have developed a model equation for periglacial semi-arid regions, akin to those of Pleistocene loess formations, and defined its range of applicability. However, despite these advances, the accuracy of the model is still limited by the low data resolution and the quality of available calibration data. To build on the previous successes and raise the data quality to a level where it can be used in Earth system models, I apply for a follow-up project. This project aims to improve the accuracy of precipitation isotope reconstructions from snail shell isotopy through sclerochronological measurements and more precise calibration data. The specific project objectives are: (1) Achieving higher temporal resolution and, consequently, greater accuracy of the isotope data through sclerochronological measurements of snail shells. For this purpose, microscopically small land snails – typical species found in loess archives – will be measured at high resolution for the first time to obtain more accurate data. (2) Increasing the accuracy of calibration data to improve the model: Recent snail shells will be sampled, and modelled long-term averages of δ18O precipitation isotopes will be replaced with measured rain isotope data for the exact location and time period of shell growth. This will be done in combination with monitoring the activity phases of reference snails to accurately correlate periods within the shells. (3) Testing the methodology on a loess archive and for Earth System modelling: (Sub)fossil snails will be isotopically analysed and compared with other proxy data. The results will be validated using the isotope-enabled Earth system model AWI-ESM-wiso to assess their precision. The expected outcomes include an improved quantitative model for calculating δ18O of precipitation from shell isotopy. These results could significantly enhance our understanding of past climatesnd help make more accurate predictions of future climate changes.

• DFG Programme: Research Grants