Centennial AMOC variability: mechanism and impacts

• Main Author: Jiang, Weimin
• 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 Universite, Francis Codron, Guillaume Gastineau
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2022
• Subjects: AMOC; North Atlantic; Climate response; Centennial variability; Atlantique Nord; Réponse climatique; Variabilité du centenaire; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Arctic; Arctic Ocean; Barents Sea; East Greenland; east greenland current; Greenland; Lincoln Sea; Sea ice
• Online Access: https://hal.science/tel-03956026; https://hal.science/tel-03956026/document; https://hal.science/tel-03956026/file/manuscript_reviewer.pdf

The mechanisms driving the Atlantic meridional overturning circulation (AMOC) low-frequency variability and the climate impact are investigated in the atmosphere-ocean coupled general circulation model (AOGCM) IPSL-CM6A-LR. A centennial to multi-centennial variability of the AMOC emerges in this model, which increases the uncertainties associated with internal variability in the climate projections. We isolate the low-frequency variations in a 2000- yr preindustrial control simulation and show the dominant role of the freshwater exchanges between the Arctic Ocean and the North Atlantic in controlling the AMOC intensity.As the AMOC increases, the ocean transports heat northward, which leads to the sea-ice melting in the Arctic Ocean. Combined with the weakened southward East Greenland Current, the freshwater export from the Arctic reduces, and a progressive accumulation of freshwater occurs in the central Arctic. Meanwhile, the saltier Atlantic inflow through the Barents Sea results in a positive salinity anomaly in the Eastern Arctic subsurface. The mean transpolar drift across the Arctic towards the Lincoln Sea tends to transport the positive salinity in the Eastern Arctic subsurface to the central Arctic and the central freshwater anomaly to the Lincoln Sea north of Greenland. In parallel, a cyclonic circulation anomaly is simulated around Greenland, which competes with the tendency of the transpolar drift transporting freshwater southward towards Greenland. This competition leads to the relatively long retainment of a surface freshwater anomaly in the Arctic Ocean. When this accumulated freshwater finally reaches the Lincoln Sea, the oceanic currents around Greenland reorganize, leading to the export of the anomalous Arctic freshwater to the North Atlantic, enhancing the stratification in deep convection sites. The AMOC then decreases, positive salinity anomalies appear in the Central Arctic, and the variability switches to the opposite phase.We further examine the climate responses to this low-frequency AMOC ...