Major changes in Biological Productivity during the Quaternary and their impacts on the carbon and oxygen cycles

• Main Author: Brandon, Margaux
• Other Authors: Géosciences Paris Saclay (GEOPS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Université Paris-Saclay, Stéphanie Duchamp-Alphonse
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2020
• Subjects: Biological productivity; Triple isotope composition of atmospheric oxygen - Δ¹⁷O of O₂; Micropaleontology; Geochemistry; Quaternary; Termination V; Productivité biologique; Composition isotopique triple de l'oxygène de l'air - Δ¹⁷O de O₂; Micropaléontologie; Géochimie; Quaternaire; Terminaison V; [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology; Antarctic; Southern Ocean; The Antarctic; Indian; Antarc*; EPICA; ice core; Sea ice
• Online Access: https://tel.archives-ouvertes.fr/tel-03505909; https://tel.archives-ouvertes.fr/tel-03505909/document; https://tel.archives-ouvertes.fr/tel-03505909/file/91137_BRANDON_2020_archivage.pdf

During glacial-interglacial cycles of the Quaternary, the atmospheric CO₂ (pCO₂) concentration is associated with important variations, in particular during transitions between glacial and interglacial periods, also called terminations, with increases of up to 100 ppm of pCO₂ in a few thousand years. While the roles of oceanic circulation and sea-ice cover on pCO₂ are studied for several years now, little is known on the impact of biological productivity. The goal of this thesis is to reconstruct the past changes in biological productivity and to estimate their contributions on atmospheric pCO₂ variations over the last 800 000 years (ka), with particular attention to Termination V (~425 ka) and Marine Isotope Stage (MIS) 11, the interglacial period around 400 ka. Two different approaches were combined to reconstruct global and local variations of biological productivity. Measurements of Δ¹⁷O of O₂ in the air trapped in the Antarctic EPICA Dome C ice core between 400 and 800 ka allowed to complete the pre-existing record and trace back variations of global biosphere productivity expressed in oxygen fluxes over the past 800 ka. Micropaleontological (coccoliths, foraminifera) and geochemical (TOC, CaCO₃, XRF) analyses were performed on a sediment core of the Indian sector of the Southern Ocean (MD04-2718) to reconstruct the changes in biological pump efficiency over the past 800 ka. The results obtained during this thesis showed that, at the scale of glacial-interglacial cycles, global biospheric productivity and Southern Ocean carbonate production are more important during interglacial periods compared to glacial periods, minimizing the impact of marine organic productivity on atmospheric pCO₂. Termination V and MIS 11 register the strongest biosphere productivity of the past 800 ka and the highest marine carbonate production of the past 9 interglacial periods in the Southern Ocean. While the important carbonate production is a source of CO₂ for the atmosphere, the rise in biosphere productivity would ...