Geochemistry of speleothems from the south-east of Europe (U-Th and 14C chronology, trace elements, 87Sr/86Sr, 18O/16O, 13C/12C) for climatic and environmental reconstructions during the Holocene

• Main Author: Drugat, Laurine
• Other Authors: Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Université Paris Saclay (COmUE), Edwige Pons-Branchu, Hélène Valladas
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2018
• Subjects: Holocene; Paleo-Reconstructions; Rare earth elements; Trace elements; Isotopic geochemistry; Speleothems; Holocène; Paléo-Reconstitutions; Terres rares; Eléments traces; Géochimie isotopique; Spéléothèmes; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; [SDU.STU.PG]Sciences of the Universe [physics]/Earth Sciences/Paleontology; North Atlantic
• Online Access: https://tel.archives-ouvertes.fr/tel-02495354; https://tel.archives-ouvertes.fr/tel-02495354v2/document; https://tel.archives-ouvertes.fr/tel-02495354v2/file/70867_DRUGAT_2018_archivage.pdf

The purpose of this thesis is to use speleothem geochemistry through a multi-proxy study to reconstruct environmental and climatic variations in southwestern Europe during the Holocene. This work, based on three sites distributed between Spain and France, covers the last 14,000 years. Due to its location at the confluence of the high and low latitudes, this region of south-western Europe is especially sensitive to both the influence of the North Atlantic climate but also the Mediterranean and subtropical African and Asian climate. This particular context allows to study ideally the impact of the different climatic mechanisms driving the modifications of its environment. The choice of the study sites’ distribution aims to compare sites with main Atlantic influence (Candamo, N Spain), Mediterranean (Salamandre cave, SE France) and mixt one (Nerjà, S Spain). The understanding of geochemical behavior was the first part of this study. After the establishment of a chronological frame (14C, U/Th), elemental geochemistry (trace elements and rare earth elements) and isotopic (87Sr/86Sr, d18O, d13C) was coupled. The 87Sr/86Sr isotope ratio, traditionally used as a source tracer for Sr, has been coupled to the study of elementary variations of alkali elements (Li, Rb, Cs) in order to determine changes in the contribution of bedrock and soil in speleothems. The behavior of these alkalis has also been shown to be related to different modes of transport (particulate dissolved or bound to organic complexes) and the use of d13C and rare earths (light rare earth and heavy rare earth fractionation and cerium anomaly) made it possible to confirm or not these hypotheses. The second part of this work was to apply these geochemical mechanisms to the determination of the hydrological and environmental processes and to place them in the specific climatic context of each study site. Thus, the alkali elements (Li, Rb, Cs) have proved to be good indicators of weathering phenomena that may be related to climate change (such as the ...