Southern Ocean link between changes in atmospheric CO 2 levels and northern-hemisphere climate anomalies during the last two glacial periods

• Published in: Quaternary Science Reviews
• Main Authors: Gottschalk, Julia, Skinner, Luke C., Jaccard, Samuel L., Menviel, Laurie C., Nehrbass-Ahles, Christoph, Waelbroeck, Claire
• Other Authors: Oeschger Centre for Climate Change Research (OCCR), Universität Bern / University of Bern (UNIBE), Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences Cambridge, UK, University of Cambridge UK (CAM)-University of Cambridge UK (CAM), Palaeontology, Geobiology and Earth Archives Research Centre (PANGEA Research Centre), School of Biological, Earth and Environmental Sciences Sydney (BEES), University of New South Wales Sydney (UNSW)-University of New South Wales Sydney (UNSW), Climate and Environmental Physics Bern (CEP), Physikalisches Institut Bern, Universität Bern / University of Bern (UNIBE)-Universität Bern / University of Bern (UNIBE), Paléocéanographie (PALEOCEAN), Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), European Project: 339108,EC:FP7:ERC,ERC-2013-ADG,ACCLIMATE(2014)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2020
• Subjects: Southern Ocean; Palaeoclimatology; Carbon cycle; Glacials; Redox-sensitive elements; Atmospheric CO2 variations; Foraminifera; Dansgaard-Oeschger cycles; Interstadials Stadials; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology; North Atlantic
• Online Access: https://hal.science/hal-02407224; https://hal.science/hal-02407224/document; https://hal.science/hal-02407224/file/Gottschalk-QSR2020_HAL.pdf; https://doi.org/10.1016/j.quascirev.2019.106067

International audience Past millennial-scale changes in atmospheric CO2 (CO2,atm) concentrations have often been attributed to variations in the overturning timescale of the ocean that result in changes in the marine carbon inventory. Yet, there remains a paucity of proxy evidence that documents changes in marine carbon storage globally, and that links them to abrupt climate variability in the northern hemisphere associated with perturbations of the Atlantic Meridional Overturning Circulation (AMOC). The last two glacial periods were suggested to differ in the spatial extent of the AMOC and its sensitivity to perturbations. This provides an opportunity to compare the nature of marine carbon cycle-climate feedbacks between them. Here, we reconstruct variations in respired carbon storage (via oxygenation) and the AMOC “geometry” (via carbonate ion saturation) in the deep South Atlantic. We infer decreases in deep South Atlantic respired carbon levels at times of weakened AMOC and rising CO2,atm concentrations during both glacial periods. These findings suggest a consistent pattern of increased Southern Ocean convection and/or air-sea CO2 fluxes during northern-hemisphere stadials accompanying AMOC perturbations and promoting a rise in CO2,atm levels. We find that net ocean carbon loss, and hence the magnitude of CO2,atm rise, is largely determined by the stadial duration. North Atlantic climate anomalies therefore affect Southern Ocean carbon cycling in a consistent manner, through oceanic (e.g., ventilation seesaw) and/or atmospheric processes (e.g., Ekman pumping).