Enhanced mercury deposition by Amazonian orographic precipitation: Evidence from high-elevation Holocene records of the Lake Titicaca region (Bolivia)

• Main Authors: Guédron, S., Ledru, M.-P., Escobar-Torrez, K., Develle, A.L., Brisset, E.
• Other Authors: Institut des Sciences de la Terre (ISTerre), Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement IRD : UR219-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes 2016-2019 (UGA 2016-2019 ), Institut des Sciences de l'Evolution de Montpellier (UMR ISEM), École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Montpellier (UM)-Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Centre National de la Recherche Scientifique (CNRS)-Institut de recherche pour le développement IRD : UR226, Environnements, Dynamiques et Territoires de la Montagne (EDYTEM), Centre National de la Recherche Scientifique (CNRS)-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2018
• Subjects: Atlantic Meridional Overturning Circulation; Climate change; stable isotopes; Central Andes; Peat sediment; Pollen; [SDE.MCG]Environmental Sciences/Global Changes; [SDE.BE]Environmental Sciences/Biodiversity and Ecology; [SDE.IE]Environmental Sciences/Environmental Engineering; [SDE.ES]Environmental Sciences/Environmental and Society; [SHS.GEO]Humanities and Social Sciences/Geography; The Altiplano; North Atlantic
• Online Access: https://hal.archives-ouvertes.fr/hal-02006591

International audience Very few studies have focused on historical mercury (Hg) deposition in the Southern Hemisphere, especially for the pre-mining period. Therefore, the respective contributions of Hg emissions from anthropogenic and natural sources are not fully constrained and the long-term influence of climate variability is still in debate. In this study, we reconstructed Hg depositions over the last 13,500 years based on two sedimentary records located at the fringe between Amazonia and the Altiplano. Multiproxy analyses carried on the same sedimentary archives (i.e. Hg accumulation rates (AR), major elements, total organic carbon, delta C-13 and pollen analyses) show evidence that Hg deposition has risen according to Amazonian orographic moisture and precipitation during the Holocene, except for the last 200 years, for which modem industry and goldmining overwhelmed the natural signal. Comparisons with existing Hg records indicated that metallurgy and volcanic emissions were not perceptible due to the eastern down-wind position of the sites. Altogether, it argues that the historical variability of Hg deposition in the central eastern Andes has been primarily driven by changes in Amazonian moisture. At least six main phases of higher Hg AR (2.6 +/- 1.4 mu m(-2) y(-1)) compared to baseline values (0.9 +/- 0.3 mu g m(-2) y(-1)) were identified over the Holocene. During the early and late Holocene, phases of higher Hg AR coincided with wet episodes recorded in Lake Titicaca and Sajama records. During the Middle Holocene arid phase, reconstructed wetter episodes by Hg together with vegetation dynamics were attributed to the set-up of moisture niches in the eastern flanks of the Andes. Comparisons to other paleoclimatic records supports the role of North Atlantic sea-surface temperature in forcing precipitation during the late Holocene period while other mechanisms allowing moisture niches by orography are discussed for the Mid-Holocene dry phase in the eastern Andes region.