Rare earth and alkali elements in stalagmites, as markers of Mediterranean environmental changes during Termination I

International audienceSpeleothems represent a key source of information on climate variations in continental environments as they enable high temporal resolution reconstructions. The stalagmite salam3 presented in this study comes from the Salamandre Cave (SE France, Gard region). Its growth period, determined by 230Th/234U chronology and MOD-AGE extrapolation, falls between 10.91 ± 1.00 kyr BP and 13.43 ± 0.25 kyr BP, which corresponds to the transition between the last glacial period and the Holocene. This period is essential for the understanding of past and future climate variations.In this study, trace elements were measured along the growth axis of this stalagmite and results were compared with the elementary composition of bedrock and soil above the cave. Three periods were identified with high Li, Rb, Cs, Th and rare earth element (REE) concentrations, between 13.43 ± 0.25 and 13.11 ± 0.27, between 12.70 ± 0.34 and 12.30 ± 0.15 kyr, and between 11.31 ± 0.86 and 11.15 ± 0.87 kyr.Our results suggest that the alkali metals (alkalis) studied are either associated in the detrital phase with the clay and particle fraction (correlation with Th), or with the organic matter and colloids as complexed ligands (correlation with Mn). To attribute the origin of REE measured within the stalagmite, we compared their pattern with those of soil and bedrock, and two sources were deduced: i) periods with an enrichment in light REE and no cerium anomaly corresponding to mobilization from soil during weathering episodes such as the Bölling-Alleröd period; ii) from bedrock during a longer residence time of water in the epikarst such as during the Younger Dryas and the Holocene. Thus, as illustrated in this study, combined analysis of REE and alkalis can provide key information on soil weathering linked to climate/environmental change