Spatial behaviour of water isotopes in past global precipitation recorded in speleothem fluid inclusions

Recovering liquid water from past precipitation on continental areas from mid- to low-latitude and analysing its water isotopes presents significant challenges. Paleoclimate archives such as groundwater, ice or speleothems provide direct access to paleowaters. Most of the paleoclimate reconstructions linked to past precipitation water isotopes are not directly based on analysis of paleo liquid water. They are measured, for instance, on carbonate, sediment or cellulose, all of which primarily derive from precipitation water, yet remain influenced by various fractionation processes during their formation.

Speleothems are advantageous as they can be found in all karstic regions of the Earth, at every latitude and on every continent. They contain fluid inclusions that encapsulated fossil drip water, corresponding to a mixture of precipitation water that fell above the cave area approximately at the time the inclusions were formed. It therefore constitutes thus a unique window into the past hydroclimate cycle for mid- to low latitude. Having better access to paleowater at lower latitudes than those of polar regions allows us to gather global information and understand the behaviour of past meteoric water.

Using published and novel speleothem fluid inclusion data from ~140 caves, we investigate the global behaviour of water isotopes in the past. We explore the spatial distribution of paleoprecipitation, construct a global meteoric water line and develop paleo-isotopic lapse rates for the Holocene and Pleistocene. Furthermore, we compare the speleothem data with observational stable isotope data and two model simulations, i.e. the AWI-ESM-wiso and the ECHAM6-wiso simulations.