Isotopic imprint and history of stratospheric volcanism recorded in Dome C, Antarctica, over the last 2600 years

• Main Author: Gautier, Elsa
• Other Authors: Laboratoire de glaciologie et géophysique de l'environnement (LGGE), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS), Université Grenoble Alpes, Joël Savarino
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2015
• Subjects: Ice; Climate; Mass spectrometry; Isotope; Sulfur; Volcanism; Volcanisme; Soufre; Spectrométrie de masse; Climat; Glace; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Antarc*; Antarctica; Antarctique*; ice core
• Online Access: https://tel.archives-ouvertes.fr/tel-01560974; https://tel.archives-ouvertes.fr/tel-01560974/document; https://tel.archives-ouvertes.fr/tel-01560974/file/GAUTIER_2015_archivage.pdf

Polar ice has proved to be a very valuable way to access Earth's volcanism history, and a large number of volcanic reconstructions are based on ice-core analysis. Reconstructions are fed into climate forcing models in order to estimate volcanic cooling effect, resulting from the interactions between volcanic sulfuric acid aerosols and incident solar radiations. In this type of reconstruction, determining the potential impact of an eruption is a key step. It usually relies on the identification of its signal in both polar caps (bipolar signal). This wide spatial distribution indeed reflects a significant residence time in the stratosphere, and thus a sizable impact on climate. However, ice cores offer an interesting alternative to this method: the analysis of volcanic sulfates reveals a mass independent fractionation of sulfur (S-MIF) in the aerosols formed in the stratosphere, allowing us to discriminate between low climatic impact (tropospheric) and high climatic impact eruptions (stratospheric). Studying the unusual isotopic signature of stratospheric aerosols simultaneously allows for constraining photochemical mechanisms responsible for this anomaly (Δ33S≠ 0), which are currently only partially identified. In 2010-2011, 5 100m-cores were drilled at Dome C, Antarctica in order to reconstruct a history of stratospheric volcanic over the past 2500 years, by the isotopic method. Drilling 5 replicate cores, 1 m apart, allowed us to study various aspects of the reconstruction.Firstly, we were able to assess the sulfate deposition variability on a local scale, and therefore the statistical representativeness of a single core in a volcanic reconstruction. Sulfate concentration analysis of the 5 cores reveals that local scale variability, essentially attributed to snow drift and surface roughness at Dome C, can lead to a non-exhaustive record of volcanic events if a single core is used; on average 30% of the volcanic events are missing per core, and the uncertainty on the volcanic flux (up to 60%) is ...