Application of Microanalytical Techniques to an Extremely Slow Growing Speleothem: a Pilot Study Covering the Last Glacial Period

Speleothems have emerged as one of the best sources of terrestrial palaeoclimate information. They have the potential to preserve long and continuous records, contain multiple climate-sensitive properties and can be accurately and precisely dated. These characteristics ideally position speleothems to refine the chronology of climate events recorded in ice and marine sediment. In recent years we have seen a dramatic improvement in analytical instrumentation available for high-resolution, in situ stable isotope and trace element analysis. These techniques present the opportunity to obtain palaeoclimate reconstructions from slow-growing speleothems, such as subaqueous deposits, which have largely been overlooked for palaeoclimate research. Here, we present the use of microanalytical techniques to obtain a ‘high-resolution’ palaeoclimate reconstruction from an exceptionally slow growing (~0.3 mm kyr^-1) subaqueous calcite mound from Corchia Cave, NW Italy. A 23-cm-long core through this speleothem provides a ~continuous climatic record extending back almost 1 Ma. In this pilot investigation, we use microanalytical techniques to obtain a palaeoclimate reconstruction from the top ~2 cm of the core, which represents the last ~120 kyr. Micron-scale trace element analyses were performed by X-ray micro-fluorescence at the ESRF (Grenoble, France), with complementary analyses using laser ablation ICPMS at the University of Melbourne (Australia). Stable oxygen isotope microanalysis was performed using the Sensitive High Resolution Ion Micro Probe Stable Isotope (SHRIMP SI) at the ANU (Canberra, Australia). This is the first time that this suite of techniques has been applied to a single specimen of speleothem calcite. High-resolution uranium-thorium dating has been undertaken to provide age constraints. This research demonstrates the potential application of multiple high-resolution analytical techniques to complex speleothems, and presents exciting opportunities to analyse slow-growing speleothems and to obtain high temporal (sub-annual) resolution palaeoclimate reconstructions. The successful application of such techniques to the Corchia speleothem will permit a unique, 1 Myr climate record to be obtained in the future.