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Impact of climate changes during the last 5 million years on groundwater in basement aquifers

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      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.

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      Most cited references 5

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      An early Cenozoic perspective on greenhouse warming and carbon-cycle dynamics.

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        Cenozoic continental climatic evolution of Central Europe.

        Continental climate evolution of Central Europe has been reconstructed quantitatively for the last 45 million years providing inferred data on mean annual temperature and precipitation, and winter and summer temperatures. Although some regional effects occur, the European Cenozoic continental climate record correlates well with the global oxygen isotope record from marine environments. During the last 45 million years, continental cooling is especially pronounced for inferred winter temperatures but hardly observable from summer temperatures. Correspondingly, Cenozoic cooling in Central Europe is directly associated with an increase of seasonality. In contrast, inferred Cenozoic mean annual precipitation remained relatively stable, indicating the importance of latent heat transport throughout the Cenozoic. Moreover, our data support the concept that changes in atmospheric CO2 concentrations, although linked to climate changes, were not the major driving force of Cenozoic cooling.
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          Sulfur isotopic composition of cenozoic seawater sulfate

          A continuous seawater sulfate sulfur isotope curve for the Cenozoic with a resolution of approximately 1 million years was generated using marine barite. The sulfur isotopic composition decreased from 19 to 17 per mil between 65 and 55 million years ago, increased abruptly from 17 to 22 per mil between 55 and 45 million years ago, remained nearly constant from 35 to approximately 2 million years ago, and has decreased by 0.8 per mil during the past 2 million years. A comparison between seawater sulfate and marine carbonate carbon isotope records reveals no clear systematic coupling between the sulfur and carbon cycles over one to several millions of years, indicating that changes in the burial rate of pyrite sulfur and organic carbon did not singularly control the atmospheric oxygen content over short time intervals in the Cenozoic. This finding has implications for the modeling of controls on atmospheric oxygen concentration.
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            Author and article information

            Affiliations
            [1]OSUR-Géosciences Rennes, Université Rennes 1 - CNRS, 35000 Rennes, France
            [2]BRGM, Laboratory Department, 3 av C. Guillemin, 45000 Orléans, France
            [3]OSUR-ECOBIO, Université Rennes 1 - CNRS, 35000 Rennes, France
            [4]Université de Nîmes, EA 7352 CHROME, 30021 Nîmes, France
            [5]CNRS/UPS UMR 8148 IDES, Université Paris-Sud, 91400 ORSAY France; P.A. GEOTOP, Université du Québec à Montréal, Montréal Qc, H3C 3P8, Canada
            [6]Aster Team Aix-Marseille Université, CNRS-IRD UM 34 CEREGE, Technopôle de l’Environnement Arbois-Méditerranée, 13545 Aix-en-Provence, France
            Author notes
            Journal
            Sci Rep
            Sci Rep
            Scientific Reports
            Nature Publishing Group
            2045-2322
            22 September 2015
            2015
            : 5
            Copyright © 2015, Macmillan Publishers Limited

            This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

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