Reconstructing hydroclimate across the Pleistocene–Holocene transition in southern Iberia using stable isotopes of gypsum hydration water

This study examines the stable oxygen and hydrogen isotopic composition of gypsum (CaSO₄·2H₂O) hydration water (GHW) preserved in sediments from the Laguna de la Ratosa playa lake (Málaga Province, southern Iberian Peninsula). The objective was to reconstruct the lake water isotopic composition between 18.5 and 7.5 ka, reflecting hydroclimate variability in the southern Iberian Peninsula during the Pleistocene-Holocene transition. The GHW proxy relies on the fact that during crystallization, gypsum incorporates water from the solution, allowing the isotopic composition of the paleo-lake water to be directly inferred from that of GHW. This is possible because the oxygen and hydrogen isotope fractionation factors between aqueous solutions and GHW are well constrained and largely insensitive to temperature and salinity. The reconstructed lake-water isotopic values show a progressive decrease (from mean values of 6 to 0‰ for δ¹⁸O and from 10 to –5‰ for δ²H) between 18.5 and 11 ka, coincident with the deglaciation. This trend indicates a transition toward less evaporative conditions associated with increasingly humid climate. Superimposed on this overall trend, however, are three arid intervals centered at ca. 18 ka, 16 ka, and 12–13 ka, during which both δ¹⁸O and δ²H values increased. These arid phases are interpreted as reflecting the influence of the Last Glacial Maximum, Heinrich Stadial 1 (HS1), and the Younger Dryas on lake hydrology. During the Early-Mid Holocene (11–7.5 ka), isotopic values stabilized at the lowest levels of the record (ca. 0‰ for δ¹⁸O and ca. –5‰ for δ²H), suggesting persistently reduced evaporation and the establishment of a more permanent lacustrine system under sustained wetter conditions. Overall, these results demonstrate that gypsum hydration water preserved in playa-lake sediments constitutes a robust proxy for reconstructing paleohydrological variability and associated climatic changes.

Acknowledgments: This study was funded by the GYPCLIMATE (PID2021-123980OA-I00) and PID2021-125619OB-C21 projects of the Spanish Ministry of Economy and Competitiveness and FEDER European Regional Development Funds. J.C.P. acknowledges the Research Teaching Training contract PRE2022-103493 Ministry of Economy and Competitiveness of Spain. L.M. was funded by the FPU21/06924 grant of the Spanish Ministerio de Educación y Formación Profesional. C.V. was funded by the European Comission (Marie Curie postdoctoral fellowship, grant no. 101063961). F.G acknowledges the Ramón y Cajal contract (RYC2020-029811-I) and the PPIT-UAL grant from the Andalusian Regional Government -FEDER2022-2026 (RyC-PPI2021-01).