A peat core Hg stable isotope reconstruction of Holocene atmospheric Hg deposition at Amsterdam Island (37.8oS)

• Published in: Geochimica et Cosmochimica Acta
• Main Authors: Li, Chuxian, Enrico, Maxime, Magand, Oliver, Araujo, Beatriz, F, Le Roux, Gaël, Osterwalder, Stefan, Dommergue, Aurélien, Bertrand, Yann, Brioude, Jérôme, de Vleeschouwer, François, Sonke, Jeroen, E
• Other Authors: Laboratoire Ecologie Fonctionnelle et Environnement (LEFE), Institut Ecologie et Environnement - CNRS Ecologie et Environnement (INEE-CNRS), Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT), Institut des sciences analytiques et de physico-chimie pour l'environnement et les materiaux (IPREM), Université de Pau et des Pays de l'Adour (UPPA)-Institut de Chimie - CNRS Chimie (INC-CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut des Géosciences de l’Environnement (IGE), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA), Laboratoire de l'Atmosphère et des Cyclones (LACy), Institut national des sciences de l'Univers (INSU - CNRS)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS)-Météo-France, Instituto Franco-Argentino sobre Estudios de Clima y sus Impactos Buenos Aires (IFAECI), Centro de Investigaciones del Mar y la Atmósfera (CIMA), Consejo Nacional de Investigaciones Científicas y Técnicas Buenos Aires (CONICET)-Facultad de Ciencias Exactas y Naturales Buenos Aires (FCEyN), Universidad de Buenos Aires Buenos Aires (UBA)-Universidad de Buenos Aires Buenos Aires (UBA)-Consejo Nacional de Investigaciones Científicas y Técnicas Buenos Aires (CONICET)-Facultad de Ciencias Exactas y Naturales Buenos Aires (FCEyN), Universidad de Buenos Aires Buenos Aires (UBA)-Universidad de Buenos Aires Buenos Aires (UBA)-Centre National de la Recherche Scientifique (CNRS), IPEV GMOSTRAL
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2022
• Subjects: Hg stable isotopes Southern Hemisphere Peat Rain Hg deposition; [CHIM.MATE]Chemical Sciences/Material chemistry; [CHIM.ANAL]Chemical Sciences/Analytical chemistry; [CHIM.POLY]Chemical Sciences/Polymers; [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry; [SDE]Environmental Sciences; Amsterdam Island
• Online Access: https://univ-pau.hal.science/hal-03906056; https://univ-pau.hal.science/hal-03906056/document; https://univ-pau.hal.science/hal-03906056/file/1-s2.0-S0016703722006305-main.pdf; https://doi.org/10.1016/j.gca.2022.11.024

International audience Mercury (Hg) stable isotopes have been broadly used to investigate the sources, transformation and deposition of atmospheric Hg during the industrial era thanks to the multiple isotope signatures deriving from mass-dependent (represented by δ202Hg) and mass-independent fractionation (represented by ΔxxxHg) in the environment. Less is known about the impact of past climate change on atmospheric Hg deposition and cycling, and whether Hg isotopes covary with past climate. Here, we investigate Hg concentration and Hg isotope signatures in a 6600-year-old ombrotrophic peat record from Amsterdam Island (AMS, 37.8oS), and in modern AMS rainfall and gaseous elemental Hg (Hg0) samples. Results show that Holocene atmospheric Hg deposition and plant Hg uptake covary with dust deposition, and are both lower under a high humidity regime associated with enhanced Southern Westerly Winds. Modern AMS gaseous Hg0 and rainfall HgII isotope signatures are similar to those in the Northern Hemisphere (NH). Holocene peat Δ199Hg and Δ200Hg are significantly correlated (R2 = 0.67, P < 0.001, n = 58), consistently oscillating between the modern Hg0 and rainfall HgII end-members. Peat Δ200Hg and Δ199Hg provide evidence of plant uptake of Hg0 as the dominant pathway of Hg deposition to AMS peatland, with some exceptions during humid periods. In contrast to NH archives generally documenting a modern increase in Δ199Hg, recent peat layers (post-1900CE) from AMS show the lowest Δ199Hg in the peat profile (−0.42 ± 0.27 ‰, 1σ, n = 8). This likely reflects a significant change in the post-depositional process on deposited anthropogenic Hg in 20th century (i.e. dark abiotic reduction), enabling more negative Δ199Hg to be observed in AMS peat. We further find that the oscillations of Hg isotopes are consistent with established Holocene climate variability from dust proxies. We suggest peat Hg isotope records might be a valid rainfall indicator.