Holocene variability of atmospheric dust and mercury in the southern hemisphere

• Main Author: Li, Chuxian
• Other Authors: Laboratoire Ecologie Fonctionnelle et Environnement (ECOLAB), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut Ecologie et Environnement (INEE), Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales Toulouse (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Université Paul Sabatier - Toulouse III, François De Vleeschouwer, Jeroen Sonke
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2019
• Subjects: Southern westerly winds; Holocene; Dust; Mercury; Mercury isotope; Peat; Vents du sud; Holocène; Poussière; Mercure; Isotopique du mercure; Tourbière; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Austral; Southern Ocean; Amsterdam Island
• Online Access: https://tel.archives-ouvertes.fr/tel-03215837; https://tel.archives-ouvertes.fr/tel-03215837/document; https://tel.archives-ouvertes.fr/tel-03215837/file/2019TOU30277.pdf

The Southern westerly winds (SWW) play an important role in regulating Southern Ocean carbon budget by enhancing the absorbance of atmospheric CO2 or resurfacing deep ocean carbon. Changes in SWW intensity are thought to determine whether Southern Ocean acts as a net CO2 sink or source, thereby affecting atmospheric CO2 concentration and then global climate. SWW also affect Southern Hemisphere (SH) dust trajectory and mercury biogeochemical cycling, which in turn can be used to trace SWW dynamics. Less is known about the past SWW variabilities and historical mercury cycle. The aim of this PhD study is to improve our understanding of the SWW trend and mercury deposition in the Holocene at remote SH sites by using geochemical and isotopic proxies in peat archives. We investigated Amsterdam Island (AMS) peat record coupled with three other peatlands in the SH mid latitudes as long-term archives of atmospheric dust and/or mercury deposition. At the northern edge of SWW and free from anthropogenic disturbance, AMS is a key site to study SWW dynamics. We find that during the Holocene, dust and mercury deposition at AMS oscillated on millennial time scales. Mercury isotope signatures, which are sensitive to rainfall inputs, indicate that high dust, high mercury events correspond to low rainfall. We suggest that these events were caused by a poleward shift of the SWW at AMS. The peat mercury records also inform on recent, human perturbation of the natural mercury cycle in the SH. We find however that the 4-fold anthropogenic mercury enrichment we observe in the SH since 1450AD, is smaller than the 16-fold enrichment in the northern hemisphere. These scientific contributions should help improve global climate models and international environmental policy under the Minamata convention on mercury. Les vents de sud-ouest (VSO) de l'hémisphère sud (HS) régularisent les cycles biogéochimiques du carbone de l'océan Austral en augmentant l'absorption du CO2 atmosphérique ou en faisant remonter les éléments nutritifs et le ...