Emergence of temperature and salinity changes in the ocean interior in response to climate change : timescales and mechanisms

• Main Author: Silvy, Yona
• Other Authors: Océan et variabilité du climat (VARCLIM), 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)-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)), 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, Eric Guilyardi, Jean-Baptiste Sallée
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2022
• Subjects: Thermohaline change; Emergence; Anthropogenic signal; Ocean interior; Modelling; Climate variability; Changements thermohalins; Émergence; Signal anthropique; Océan intérieur; Modélisation; Variabilité climatique; [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph]; [SDE.MCG]Environmental Sciences/Global Changes; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; North Atlantic; Southern Ocean
• Online Access: https://theses.hal.science/tel-03828354; https://theses.hal.science/tel-03828354/document; https://theses.hal.science/tel-03828354/file/SILVY_Yona_these_2022.pdf

Human-induced climate change is already affecting every inhabited region of the planet. Yet, over 90% of the excess heat associated with human activities has been absorbed by the ocean since the 1970s, which acts to largely damp atmospheric warming, but has large impacts on human societies and marine life. In this thesis, I explore when and where thermohaline changes in the ocean interior become large enough to be unambiguously set apart from internal variability and investigate their associated physical drivers, using ensembles of climate models and dedicated numerical experiments. We find that the climate signal in the upper ocean water-masses emerges between the late 20th century and the first decades of the 21st. The Southern Hemisphere mid-latitude Mode Waters emerge before their Northern Hemisphere counterparts. The associated warming at these timescales is mostly caused by the uptake of heat from the atmosphere, passively transported into the ocean interior. In the deeper parts of the ocean, circulation changes play a more important role in the emergence timescales of the climate signals. Increased buoyancy gain at the surface in the subpolar areas cause a slowdown in the meridional overturning circulation. This warms the subsurface and abyssal waters in the Southern Ocean as soon as the mid-20th century, adding up to the weaker passive uptake of heat, but counteracts it in the deep North Atlantic over the 21st, delaying the emergence. Although climate models miss some important aspects of the ocean response to climate change, they allow to shed light on the balance of processes at play, and suggest anthropogenic influence has already spread to large parts of the ocean. Le changement climatique d’origine humaine impacte déjà toutes les régions habitées de la planète. 90% de l’excès de chaleur associé aux activités humaines a été absorbé par l’océan depuis les années 1970, atténuant en grande partie le réchauffement atmosphérique, mais impactant fortement les sociétés humaines et la vie marine. Dans ...