title: Impact of climate changes during the last 5 million years on groundwater in basement aquifers.
abstract: Climate change is thought to have major effects on groundwater resources. There is however a limited knowledge of the impacts of past climate changes such as warm or glacial periods on groundwater although marine or glacial fluids may have circulated in basements during these periods. Geochemical investigations of groundwater at shallow depth (80-400 m) in the Armorican basement (western France) revealed three major phases of evolution: (1) Mio-Pliocene transgressions led to marine water introduction in the whole rock porosity through density and then diffusion processes, (2) intensive and rapid recharge after the glacial maximum down to several hundred meters depths, (3) a present-day regime of groundwater circulation limited to shallow depth. This work identifies important constraints regarding the mechanisms responsible for both marine and glacial fluid migrations and their preservation within a basement. It defines the first clear time scales of these processes and thus provides a unique case for understanding the effects of climate changes on hydrogeology in basements. It reveals that glacial water is supplied in significant amounts to deep aquifers even in permafrosted zones. It also emphasizes the vulnerability of modern groundwater hydrosystems to climate change as groundwater active aquifers is restricted to shallow depths.
authors.affiliation: OSUR-Géosciences Rennes, Université Rennes 1 - CNRS, 35000 Rennes, France.
authors.forename: Luc
authors.initials: L
authors.lastname: Aquilina
authors.affiliation: OSUR-Géosciences Rennes, Université Rennes 1 - CNRS, 35000 Rennes, France.
authors.forename: Virginie
authors.initials: V
authors.lastname: Vergnaud-Ayraud
authors.affiliation: OSUR-Géosciences Rennes, Université Rennes 1 - CNRS, 35000 Rennes, France.
authors.forename: Antoine Armandine
authors.initials: AA
authors.lastname: Les Landes
authors.affiliation: BRGM, Laboratory Department, 3 av C. Guillemin, 45000 Orléans, France.
authors.forename: Hélène
authors.initials: H
authors.lastname: Pauwels
authors.affiliation: OSUR-Géosciences Rennes, Université Rennes 1 - CNRS, 35000 Rennes, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Davy
authors.affiliation: BRGM, Laboratory Department, 3 av C. Guillemin, 45000 Orléans, France.
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Pételet-Giraud
authors.affiliation: OSUR-Géosciences Rennes, Université Rennes 1 - CNRS, 35000 Rennes, France.
authors.forename: Thierry
authors.initials: T
authors.lastname: Labasque
authors.affiliation: OSUR-Géosciences Rennes, Université Rennes 1 - CNRS, 35000 Rennes, France.
authors.forename: Clément
authors.initials: C
authors.lastname: Roques
authors.affiliation: OSUR-Géosciences Rennes, Université Rennes 1 - CNRS, 35000 Rennes, France.
authors.forename: Eliot
authors.initials: E
authors.lastname: Chatton
authors.affiliation: OSUR-Géosciences Rennes, Université Rennes 1 - CNRS, 35000 Rennes, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Bour
authors.affiliation: OSUR-ECOBIO, Université Rennes 1 - CNRS, 35000 Rennes, France.
authors.forename: Sarah
authors.initials: S
authors.lastname: Ben Maamar
authors.affiliation: OSUR-ECOBIO, Université Rennes 1 - CNRS, 35000 Rennes, France.
authors.forename: Alexis
authors.initials: A
authors.lastname: Dufresne
authors.affiliation: Université de Nîmes, EA 7352 CHROME, 30021 Nîmes, France.|Aster Team Aix-Marseille Université, CNRS-IRD UM 34 CEREGE, Technopôle de l'Environnement Arbois-Méditerranée, 13545 Aix-en-Provence, France.
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Khaska
authors.affiliation: Université de Nîmes, EA 7352 CHROME, 30021 Nîmes, France.|Aster Team Aix-Marseille Université, CNRS-IRD UM 34 CEREGE, Technopôle de l'Environnement Arbois-Méditerranée, 13545 Aix-en-Provence, France.
authors.forename: Corinne
authors.initials: C
authors.lastname: Le Gal La Salle
authors.affiliation: CNRS/UPS UMR 8148 IDES, Université Paris-Sud, 91400 ORSAY France; P.A. GEOTOP, Université du Québec à Montréal, Montréal Qc, H3C 3P8, Canada.
authors.forename: Florent
authors.initials: F
authors.lastname: Barbecot