Speleothem Fluid Inclusion Isotope Analysis: A Powerful Tool for Reconstructing the Climate of the Past

Seminar by Jasper Wassenburg from Max Planck Institute for Chemistry

22 November 2019
KST 10:00 – 11:00

The Seminar is being held in Room 1010 (Jasmin) – Integrated mechanical engineering building. Click here for the campus map.

Speleothem oxygen isotope records from the Asian Monsoon (AM) region cover the last 640.000 years and are important to understand teleconnection patterns across the globe. The δ18O of speleothem calcite replicates across China and are generally assumed to reflect changes in the δ18O of meteoric rainfall, which are controlled by the Asian Monsoon. However, the true variability of rainfall δ18O is unknown, because speleothem calcite rarely precipitates in equilibrium with its parent water. Speleothem calcite incorporates microscopic amounts of water that represent fossil rainfall. With fluid inclusion isotope analysis their hydrogen and oxygen isotope composition can be analysed, which allows to reconstruct the isotopic composition of rainfall back in time.

This study illustrates the power of this novel technique when applied to iconic Chinese speleothems that cover Termination II (TII). Ice age terminations in the AM region are characterized by large calcite δ18O shifts of 4 to 7‰. The δ18O composition of the fluid inclusions, however, show less variability indicating that processes acting within the cave environment are much more important than formerly assumed. Importantly, the change in isotope fractionation is highly consistent among three different caves, despite the different amplitudes in calcite δ18O. The amount of isotope fractionation within the cave environment is thus driven by climate change. We conclude that changes in kinetic isotope effects are controlled by the strength of the AM. These kinetic isotope effects amplify the AM signal observed in rainfall δ18O. Calcite δ18O is thus an extremely sensitive proxy for AM strength across TII.