Chronological and biogeochemical constraints by methane in the ice cores : application to the drillings of the EPICA project

• Main Author: Loulergue, Laetitia
• Other Authors: Laboratoire de glaciologie et géophysique de l'environnement (LGGE), 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 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)-Centre National de la Recherche Scientifique (CNRS), Université Joseph-Fourier - Grenoble I, Jerome Chappellaz([e-mail])
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2007
• Subjects: Methane cycle; Greenhouse gases; Gas chronologies; Firn densification; Ice cores; Cycle du méthane; Gaz à effet de serre; Chronologies gaz; Densification du névé; Carottes de glace; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Antarc*; Antarctic; Antarctica; Dronning Maud Land; EPICA; Greenland
• Online Access: https://theses.hal.science/tel-00329799; https://theses.hal.science/tel-00329799/document; https://theses.hal.science/tel-00329799/file/THESE_Loulergue.pdf

With the start of the 21st century, it becomes obvious that human activities directly or indirectly impact the climate system. It is thus of high priority to improve future climate simulations and their consequences. Part of this priority relies on exploring the past. Air extracted from polar ice in Greenland and Antarctica is a fantastic recorder of past changes in the Earth's atmospheric composition. Data obtained on several ice cores have shown a strong correlation between the mixing ratio of greenhouse gases (CO2, CH4, N2O) and temperature, on a time scale of hundreds of thousands of years. These data have revealed that the currently elevated greenhouse gas mixing ratios had no equivalent over the last 650'000 years, within the resolution limit of the records. Lastly, these records offer the opportunity to better understand the link between climate and the biogeochemical cycles responsible for past greenhouse gas changes, which may feedback on the future climate. Our PhD work consisted first in measuring at high temporal resolution methane in air bubbles of the new drilling sites EPICA, at Dome C and at Dronning Maud Land. These measurements allowed us (i) to propose a scheme for the causes of the methane / climate link during the last 800'000 years, and (ii) to improve the chronologies of trapped gases in ice cores, and in parallel to discuss the sequence of climatic events recorded in both hemispheres and in Antarctic ice cores. We conclude that the low frequency modulation of methane mixing ratios is probably linked to the variability of Asian monsoon and to the shift of the Intertropical Convergence Zone. Superimposed on this low frequency modulation, high latitudes wetlands may have switched on and off during major transitions between glacial and interglacial conditions. At millennial time scale, we show the ubiquity of rapid climate changes during the last eight glacial periods, and the probable persistence of the bipolar seesaw mechanism of energy redistribution between the two poles. Calculations of ...