Luc Aquilinaa,1, Virginie Vergnaud-Ayraud1, Antoine Armandine Les Landes1, Hélène Pauwels2, Philippe Davy1, Emmanuelle Pételet-Giraud2, Thierry Labasque1, Clément Roques1, Eliot Chatton1, Olivier Bour1, Sarah Ben Maamar3, Alexis Dufresne3, Mahmoud Khaska4,6, Corinne Le Gal La Salle4,6, Florent Barbecot5
22 September 2015
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.