Evaluating the role of orbitally-induced paleoceanographic changes in subtropical South Atlantic for the global climate over the last 800,000 years

• Main Author: Ballalai, João Marcelo
• Other Authors: Geo-Ocean (GEO-OCEAN), Université de Bretagne Sud (UBS)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Université de Bretagne occidentale - Brest, Universidade Federal Fluminense (Brésil), Stéphan Jorry, Ana Luiza Albuquerque
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2023
• Subjects: Atlantic meridional overturning circulation; Orbital cycles; South Atlantic subtropical gyre; Interhemispheric heat transfer; South Atlantic controls on climate; Mg/Ca analysis; Circulation méridienne de l'Atlantique; Cycles orbitaux; Gyre Subtropical de l'Atlantique Sud; Transfert de chaleur inter-hémisphérique; Contrôles de l'Atlantique Sud sur le climat; Analyses de Mg/Ca; Circulação de revolvimento meridional do Atlântico; Ciclos orbitais; Giro subtropical do Atlântico Sul; Transferência de calor inter-hemisférica; Controles do Atlântico Sul no clima; Análise de Mg/Ca; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Antarctic; Antarc*; North Atlantic Deep Water; North Atlantic; Sea ice
• Online Access: https://theses.hal.science/tel-04261916; https://theses.hal.science/tel-04261916/document; https://theses.hal.science/tel-04261916/file/These-2023-SML-Geosciences_marines-BALLALAI_Joao.pdf

Anthropogenic activity has reshaped Earth's climate by increasing atmospheric CO2 and global warming, often linked to an Atlantic Meridional Overturning Circulation (AMOC) slowdown. The AMOC redistributes heat and carbon via the South Atlantic Subtropical Gyre (SASG), acting with the Intertropical Convergence Zone (ITCZ), pursuing global energy equilibrium. Orbital variations can induce long-term climate shifts through insolation changes. This thesis investigates orbital influences on subtropical South Atlantic paleoceanography over 800 ka, analyzing benthic and planktic foraminifera δ18O, δ13C from GL-854 and MD08-3167 cores and thermocline Mg/Ca temperature from MD08- 3167. This framework unveils orbital-scale deep-water and ocean-atmosphere processes and controls on the Benguela Upwelling System (BUS), exploring AMOC's connections to climate. Chapters 1 to 3 set objectives, methods, and results. Chapter 4 explores 770 ka deep-water dynamics, where four AMOC modes controlled by orbitally-induced changes in Antarctic sea ice are proposed. The provided framework connects deep water, sea-ice, and ocean-atmosphere dynamics, shaping the Late Pleistocene climate. Chapter 5 discusses 365 ka of BUS variability. Intensified North Atlantic deep-water formation during positive precession periods enhances inter-hemispheric energy transfer, shifting SASG and ITCZ northwards, boosting upwelling. The mechanism controlling BUS connects AMOC intensity and global atmospheric patterns to atmospheric CO2 decline. Chapter 6 outlines Mg/Ca protocol performed on ICP-MS at IFREMER. Merging both surface and deep water perspectives seeks to clarify mechanisms controlling AMOC for the global climate. Les activités anthropiques ont remodelé le climat de la Terre en augmentant le CO2 atmosphérique et le réchauffement climatique, souvent lié au ralentissement de la circulation méridionale de renversement de l'Atlantique (AMOC). L'AMOC redistribue la chaleur et le carbone via le gyre subtropical de l'Atlantique Sud (SASG), agissant avec ...