Fossil water in large stalagmite voids as a tool for paleoprecipitation stable isotope composition reconstitution and paleotemperature calculation

The deuterium content of macroscopic fluid inclusions, several millimetres large, observed on two stalagmite polished sections has been measured with high accuracy (<±0.5‰). Although several recent studies have already focused on the stable isotope content of microscopic fluid inclusions, this is the first time that such measurements have been made on large inclusions by direct injection of the water in the spectrometer, eliminating technical problems due to the extraction of water from microscopic inclusions (crushing and heating). The first results from four fluid inclusions of two stalagmites of South Western and Southern France demonstrate that: (1) for the same stalagmite and the same age, the deuterium content is similar; (2) the fluid inclusion deuterium content difference between the sites is in agreement with the present day dripping water; (3) calculated paleotemperatures at 100 ka are in the range of those derived from pollen, marine and ice core records. Despite the fact that macroscopic fluid inclusions have rarely been observed, it appears that they can give precious data for paleoclimatologists on the stable isotope content (δ18O, δD and deuterium excess d) of the past cave dripping water, which is a proxy of the rainfall water, and that it can be accurately dated by the TIMS U/Th method on the host calcite up to 500 ka.