3 Hydroclimates: from present to past

This area of research focuses on understanding the mechanisms controlling the water cycles in continental and marine environments and on reconstructing past hydroclimates. In recent years, our team has developed an original tool for reconstructing evaporation within the water cycle and, ultimately, past atmospheric relative humidity, a key parameter of the climate system (ANR HUMI-17 project, led by Anne Alexandre). This method is based on the analysis of the triple isotopic composition of oxygen (17O-excess), whose variation processes within the different compartments of the water cycle (vapour, precipitation, soils, plants) and phytoliths have been defined in controlled, natural and modelled environments. The recent DIAT-17 project (LEFE-INSU, 2022-2023), led by Anne Alexandre and Florence Sylvestre, aims to assess the potential of diatom 17O-excess analysis to reconstruct the amplitude of lake water evaporation. The ANR PAST-17 project, funded in 2022 and led by Anne Alexandre, uses the calibrations resulting from the previous projects to reconstruct past hydroclimates on different timescales, in the intertropical and Mediterranean zones, in interaction with changes in vegetation and the impact of man. This research direction has been strengthened by the recent recruitment of Julie Aleman (CR CNRS, 2022), an ecologist who is using the 17O-excess of phytoliths to decouple the signals of vegetation, climate and man in Quaternary archives.
The WAO project (funded by AFALULA), led by Pierre Deschamps, aims to improve understanding of the hydrological functioning of the Saq aquifer in the Al Ula region (Saudi Arabia) in order to move towards sustainable management of this resource, which is essential for the socio-economic and agricultural development of this oasis. This theme of hydrological cycles in semi-arid to arid zones is also being strengthened by the establishment of the Viabeleaux LMI (2020-2024) in Chad, led by Florence Sylvestre.