L'air piégé dans les glaces polaires: Contraintes chronologiques et caractérisation de la variabilité climatique rapide

• Main Author: Capron, Emilie
• Other Authors: Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Université de Versailles-Saint Quentin en Yvelines, Valérie Masson-Delmotte
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2010
• Subjects: air isotopes; Antarctica; bipolar seesaw pattern; climatic variability at millennial and sub-millennial scale; dating; firn; glacial period; Greenland; last glacial inception; ice core; methane; Antarctique; carotte de glace; Dansgaard-Oeschger; datation; entrée en glaciation; Groenland; instabilités climatiques abruptes; isotopes de l'air; méthane; névé; période glaciaire; bascule bipolaire; paléoclimat; [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology; Antarctic; Dronning Maud Land; Antarc*; Antarctique*; EPICA; Greenland ice cores
• Online Access: https://tel.archives-ouvertes.fr/tel-00579600; https://tel.archives-ouvertes.fr/tel-00579600/document; https://tel.archives-ouvertes.fr/tel-00579600/file/memoire-these-CAPRON.pdf

Polar regions are particularly sensitive to the present climate change because of amplification mechanisms at play. Ice cores from Antarctica and Greenland provide precious archives of paleoclimatic variations at these high latitudes but also provide information on environmental changes at lower latitudes. This work takes advantage of information inferred from the air trapped in ice: the elemental and isotopic composition of air (N2, O2, Ar and Kr) and the methane concentration. Our results provide new insights on three different issues: (i) Past dynamic of Antarctic firn. Measurements of krypton isotopes provide direct evidences for the presence of a deep convective zone (20-50m) in the firn at Dome C during glacial periods. Based on nitrogen isotopic profiles ("15N) from EPICA Dronning Maud Land (EDML) and TALDICE ice cores, we suggest that the evolution of the firn structure is mainly controlled by accumulation rate only below a threshold in accumulation defined at 5 ±1.5 cm ice equivalent yr-1. (ii) Ice core dating. We present the first record of #O2/N2 over the EDC ice core covering the period between 300 and 800 ka. Even if we call for cautiousness in the use of this parameter as an orbital dating tool during periods characterized by a low eccentricity, the "O2/N2 is a useful tool to test the current EDC3 chronology. By coupling the isotopic composition of atmospheric oxygen and methane concentration, we synchronise the EDML (Antarctica) and NorthGRIP (Greenland) ice cores between 75 000 and 123 000 years with an associated uncertainty smaller than 400 years. (iii) This common timescale enables us to depict the abrupt climatic variability at the beginning of the last glacial period. We evidence sub-millennial scale climatic variations superimposed to the classical Dansgaard-Oeschger (DO) event succession, i.e. precursor-type peak events preceding some DO events and rebound-type climatic events at the end of the interstadial phase. We demonstrate that the bipolar seesaw pattern between Antarctica and ...