Variability and Changes of Hydrography and Circulation in the Subpolar Southern Ocean

• Main Author: Auger, Matthis
• 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), Institut Polytechnique de Paris (IP Paris)-Institut Polytechnique de Paris (IP Paris)-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), Institut Polytechnique de Paris (IP Paris)-Institut Polytechnique de Paris (IP Paris)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Sorbonne Université, Jean-Baptiste Sallée
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2022
• Subjects: Southern Ocean; Satellite altimetry; Ocean-atmosphere-cryosphere interactions; Océan austral; Circulation subpolaire; Tendances de température; Changements à long terme; Altimétrie satellitaire; Variabilité saisonnière; Variabilité méso-échelle; Interactions océan-atmosphère-cryosphère; [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph]; Antarc*; Antarctic; Ice Shelves; Sea ice
• Online Access: https://theses.hal.science/tel-03700638; https://theses.hal.science/tel-03700638/document; https://theses.hal.science/tel-03700638/file/AUGER_Matthis_these_2022.pdf

The Southern Ocean is central to the global oceanic circulation and climate. This region is however on the frontline of human-induced climate change, through intense uptake of anthropogenic heat and carbon. Consequently, the Southern Ocean has experienced important changes in its hydrography and circulation over the last decades. Its subpolar part, south of the Antarctic Circumpolar Current, hosts large circulation systems of importance for the production of water masses and their associate heat and carbon content, for ocean interactions with sea-ice and ice-shelves, and consequently for global mean sea level. Observations are still sparse in that region, particularly in wintertime when it is covered by sea ice. Thus, the regional response of the subpolar Southern Ocean hydrography and circulation to interactions with the atmosphere, cryosphere, and background circulation at various spatial and time scales is still under active research.In this thesis, I contribute to observing the variability and long-term changes of the hydrography and circulation of the subpolar Southern Ocean, and to unveil the mechanisms driving their variability. I first observe the long-term temperature changes in the upper layer of the Southern Ocean, from repeated ship-based measurement transects over 25 years. Besides previously documented trends, I refine the monitoring on the still poorly observed warming and shallowing of the warm subsurface water of the Southern Ocean. The long term warming is stronger than interannual variability, and the shallowing rate is 3 to 9 times the previously estimated one. In a second part, I develop and exploit an ocean topography dataset, spanning six years of measurements over the whole Southern Ocean south of 50°S. This dataset allows me to explore the variability of the subpolar Southern Ocean circulation, particularly the seasonal cycle of the large-scale circulation and the mesoscale variability under sea ice. At the seasonal scale, the circulation of the Weddell and Ross gyres, and the Antarctic ...