Early to Middle Holocene aridification trend in southeastern Iberia and the termination of the last North African Humid Period revealed by a multi-proxy speleothem record

Abstract. During the Early Holocene, relatively humid conditions prevailed across northern Africa, transitioning to a drier climate by the end of the mid-Holocene. While the timing and nature of this climatic shift are well-established in the Maghreb region of Africa, uncertainties remain regarding the pace of the wet-to-dry transition in the southern Iberian Peninsula. We present a multi-proxy stalagmite record from Simarrón II cave, spanning 9.7 to 4.4 ka BP. The dataset combines stable carbon and oxygen isotopes in calcite (δ¹⁸O_carb, δ¹³C), Mg/Ca ratios, petrographic observations, fluid inclusion isotopes (δ¹⁸O_fi, δ²H) and TEX₈₆-derived paleotemperatures to reconstruct paleohydrological and climatic changes. From 9.7 to 4.4 ka, progressively higher δ¹⁸Ofi and δ²H values, coupled with decreasing deuterium excess, are consistent with a gradual shift in rainfall seasonality and/or moisture sources (i.e., frontal Atlantic-type precipitation regime during the early Holocene to a more convective Mediterranean regime). This trend could be overprinted by enhanced soil and in-cave water evaporation during the late Mid-Holocene because of climate aridification. Lower δ¹⁸O_carb, δ¹³C, and Mg/Ca values between 9.7 and 6.0 ka also indicate relatively wet conditions during the early Holocene and part of the middle Holocene. From ~6.0 ka onward, these proxies show a progressive increase, stabilizing after ~5.5 ka, consistent with a climate shift toward more arid conditions that occurred within ~500 yrs. This is interpreted as reflecting enhanced prior calcite precipitation rates and kinetic isotope effects associated with intensified in-cave CO₂ degassing, due to the dry climate during the termination of the last North African Humid Period. Paired δ¹⁸O_carb– δ¹⁸O_fi paleotemperature estimates yield unrealistically high values (20–30 °C) for most of the investigated period, further supporting non-equilibrium fractionation processes and likely in-cave water evaporation. In contrast, TEX₈₆-based temperatures (13–17 °C) suggest that early–mid Holocene cave temperatures were higher than present-day values in the cave (11.7 °C).