Paleoclimatic significance of water isotopes in speleothem fluid inclusions

Speleothems (cave carbonate) contain fluid inclusions that are natural repositories of cave drip water and precipitation respectively. This water is stored within the speleothem calcite matrix and well preserved from post-depositional alterations in cave environments. Extracting the water and analysing its isotopes provide direct information about the hydrological cycle on timescales ranging from months to millions of years (>10⁶ years). Therefore, speleothem fluid inclusions offer the opportunity to address key questions about paleorainfall and paleotemperatures, as water isotopes can be used to reconstruct temperatures or origin of moisture at the time of calcite deposition. This review aims to explore the background and history of speleothem fluid inclusion science and the development of analytical methods and records, thereby giving new insights into the potential of fluid inclusions. Based on a compilation of available speleothem fluid inclusion water isotopes, we developed a paleo-Global Meteoric Water Line (paleo-GMWL) that shows a similar slope to modern precipitation which corroborates the potential of fluid inclusions in the reconstruction of past precipitation. Similarly, first spatial observations seem to highlight the potential of fluid inclusions to contribute to a Global Network of Isotopes in Precipitation in the past (paleo-GNIP). Recent analytical developments will further enable the production of highly-resolved water isotope records for continental areas. Therefore, overall, there is a great potential in the use of speleothem fluid inclusions in paleoclimate sciences, which will provide information about past climate and allow data-model comparisons.