Reconstructions of past ocean circulation at glacial-interglacial timescale: development and use of geochemical and geochronological proxies to sedimentary archives

• Main Author: Sepulcre, Sophie
• 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), Université Paris-Saclay, Edwige Pons-Branchu
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2023
• Subjects: Paleoclimatology (Quaternary); Sediment records; Micropaleontology (foraminifers); Isotopic and elemental geochemistry; Geochronology; Enregistrements sédimentaires; Micropaléontologie (Foraminifères); Géochimie isotopique et élémentaire; Géochronologie (Quaternaire); [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; [SDU.STU.PG]Sciences of the Universe [physics]/Earth Sciences/Paleontology; Indian; Southern Ocean; North East Atlantic; Planktonic foraminifera
• Online Access: https://hal.science/tel-04533654; https://hal.science/tel-04533654/document; https://hal.science/tel-04533654/file/SEPULCRE_MANUSCRIT%20HDR_2023_FINAL.pdf

Reconstructing past climate variations is the key to understand future changes and predict them through modelling. The role of the different players of this complex system, and their interactions via the flux of energy and matter such as through the carbon cycle, remain to be clarified. Thus, the impact of the changes in the water masses circulation and of the ocean as a pool, must be better documented. To achieve this objective, my research work has essentially focused on i) better understanding the role of the circulation of subsurface and intermediate water masses on the climate system at glacial-interglacial timescale, ii) the reconstruction of the variations in the connections between the different ocean basins via these water masses and iii) the highlighting of interactions that exist between changes in the dynamics of these water masses and the carbon cycle. To achieve these goals, I have particular interest in the development and optimization of geochemical proxies and geochronological tools dedicated to paleoenvironmental reconstructions and the temporal adjustment of sedimentary archives, respectively. I use the Carbon (δ$^{13}$C) and Oxygen (δ$^{18}$O) stable isotopes, elemental ratios (e.g., Mg/Ca, Sr/Ca, Cd/Ca, Mg/Li, U/Ca) and $^{14}$C ages measured on benthic and planktonic foraminifera. I worked on various projects thanks to the (co-) supervision of (defended and in progress) PhD and M2 internships, and to the support of financial programs, focused on the Indian Ocean (North and Equatorial), the North-East Atlantic Ocean and other areas are being studied or planned in the Mediterranean Sea and in the Southern Ocean. Our results have especially better documented the role of subsurface and intermediate water masses since the Last Glacial Maximum Reconstituer les climats du passé est la clé de la compréhension des changements futurs et de leur prévision par la modélisation. Le rôle des différents compartiments de ce système complexe, et leurs interactions via des échanges d’énergie et de matière ...