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Hydrogeological control on carbon dioxide input into the atmosphere of the Chauvet-Pont d'Arc cave

Abstract : Carbon dioxide (CO 2) concentration (CDC) is an essential parameter of underground atmospheres for safety and cave heritage preservation. In the Chauvet cave (South France), a world heritage site hosting unique paintings dated 36,000 years BP, a high-sensitivity monitoring, ongoing since 1997, revealed: 1) two compartments with a spatially uniform CDC, a large volume (A) (40,000 to 80,000 m 3) with a mean value of 2.20 ± 0.01% vol. in 2016, and a smaller remote room (B) (2000 m 3), with a higher mean value of 3.42 ± 0.01%; 2) large CDC annual variations with peak-to-peak amplitude of 2% and 1.6% in A and B, respectively; 3) long-term changes, with an increase of CDC and of its annual amplitude since 1997, then faster since 2013, reaching a maximum of 4.4% in B in 2017, decreasing afterwards. While a large effect of seasonal ventilation is ruled out, monitoring of seepage at two dripping points indicated that the main control of CDC seasonal reduction was transient infiltration. During periods of water deficit, calculated from surface temperature and rainfall, CDC systematically increased. The carbon isotopic composition of CO 2 , correlated with water excess, is consistent with a time-varying component of CO 2 seeping from above. The CO 2 flux, which is the primary driver of CDC in A and B, inferred using box modelling, was found to confirm the relationship between water excess and reduced CO 2 flux into A, compatible with a more constant flux into B. A buoyancy-driven horizontal CO 2 flow model in the vadose zone, hindered by water infiltration, is proposed. Similarly, pluri-annual and long-term CDC changes can likely be attributed to variations of water excess, but also to increasing vegetation density above the cave. As CDC controls the carbonate geochemistry, an increased variability of CDC raises concern for the preservation of the Chauvet cave paintings.
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Contributor : Dominique Genty Connect in order to contact the contributor
Submitted on : Monday, December 28, 2020 - 1:55:22 PM
Last modification on : Monday, August 29, 2022 - 2:34:07 PM
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François Bourges, Dominique Genty, Frédéric Perrier, Bruno Lartiges, Édouard Régnier, et al.. Hydrogeological control on carbon dioxide input into the atmosphere of the Chauvet-Pont d'Arc cave. Science of the Total Environment, Elsevier, 2020, 716, pp.136844. ⟨10.1016/j.scitotenv.2020.136844⟩. ⟨hal-03089428⟩



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