Mechanisms controlling anthropogenic CO2 uptake and acidification in North Atlantic and Southern Indian Ocean waters

• Main Author: Leseurre, Coraline
• Other Authors: Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-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)-École polytechnique (X)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-École normale supérieure - Paris (ENS-PSL), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Sorbonne Université, Gilles Reverdin, Claire Lo Monaco
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2022
• Subjects: North Atlantic subpolar gyre; Southern Indian Ocean; Anthropogenic carbon; Ocean acidification; Oceanic Suess effect; Times series; Gyre subpolaire nord Atlantique; Océan Indien Austral; Carbone anthropique; Acidification des océans; Effet Suess océanique; Séries temporelles; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDE.MCG]Environmental Sciences/Global Changes; North Atlantic; Southern Ocean
• Online Access: https://theses.hal.science/tel-04028410; https://theses.hal.science/tel-04028410/document; https://theses.hal.science/tel-04028410/file/LESEURRE_Coraline_these_2022.pdf

The ocean plays a very large role in the climate system due to the large exchange of carbon dioxide with the atmosphere and the recent shift of the exchanges towards a large oceanic sink of CO2 in the Anthropocene era. The North Atlantic and the Southern oceans are acknowledged to be major repositories of this anthropogenic carbon (Cant). Indeed, ~25% of the Cant penetrates through the surface waters of the North Atlantic and ~40% reside in the intermediate and mode waters of the Southern ocean. It has been established that this oceanic carbon sink presents a large time variability of seasonal to multidecadal times scales, but that is poorly known, resulting in large uncertainties in long term climate predictions. It has thus been recommended to focus observing efforts in the regions where the absorption of CO2 is large: the North Atlantic and the Southern oceans. In this frame, the study of the seasonal to decadal variability of the oceanic carbonate system is required to better understand the effects of current changes on the oceanic carbon cycle. I use data collected since the mid-1990s until 2021 within the framework of the two French surveys SURATLANT and OISO, in order to describe the spatial and temporal variability of parameters of the carbonate system (AT, CT, fCO2, pH and δ13CDIC) in the North Atlantic subpolar gyre (NASPG) as well as in the Indian sector of the Southern Ocean. I studied the physical and biogeochemical processes that control the evolution of fCO2, water acidification and the oceanic Suess effect, separating the anthropogenic induced changes from natural variability. The long-term evolution of fCO2 and pH during the period samples has a similar magnitude to the atmospheric CO2 increase and the overall surface ocean trends. Nonetheless, results can differ from this average view, depending on season, the particular region or specific periods. Cant increase has been identified as the prime driver controlling the observed changes in fCO2 and pH, but other processes modulate these ...