Early Eocene Ocean meridional overturning circulation: The roles of atmospheric forcing and strait geometry

• Published in: Paleoceanography and Paleoclimatology
• Main Authors: Zhang, Yurui, de Boer, Agatha, M., Lunt, Daniel, J., Hutchinson, David, K., Ross, Phoebe, Flierdt, Tina, Sexton, Philip, Coxall, Helen, Steinig, Sebastian, Ladant, Jean-Baptiste, Zhu, Jiang, Donnadieu, Yannick, Zhang, Zhongshi, Chan, Wing‐le, Abe‐ouchi, Ayako, Niezgodzki, Igor, Lohmann, Gerrit, Knorr, Gregor, Poulsen, Christopher, J., Huber, Matt
• Other Authors: State Key Laboratory of Marine Environmental Science (MEL), Xiamen University, Bolin Centre for Climate Research, Stockholm University, School of Geographical Sciences Bristol, University of Bristol Bristol, Climate Change Research Centre Sydney (CCRC), University of New South Wales Sydney (UNSW), Department of Earth Science and Engineering Imperial College London, Imperial College London, The Open University Milton Keynes (OU), 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), Modélisation du climat (CLIM), 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)), National Center for Atmospheric Research Boulder (NCAR), Centre Européen de Recherche et d'Enseignement des Géosciences de l'Environnement (CEREGE), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Collège de France (CdF (institution))-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), China University of Geosciences Wuhan (CUG), Atmosphere and Ocean Research Institute Kashiwa-shi (AORI), The University of Tokyo (UTokyo), Alfred Wegener Institute, Bremerhaven, Institute of Geological Sciences Wrocław (UWr), University of Wrocław Poland (UWr), University of Michigan Ann Arbor, University of Michigan System, Department of Earth, Atmospheric, and Planetary Sciences West Lafayette (EAPS), Purdue University West Lafayette
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2022
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces; environment; Pacific; Southern Ocean; North Atlantic
• Online Access: https://hal.science/hal-03598897; https://hal.science/hal-03598897/document; https://hal.science/hal-03598897/file/Paleoceanog%20and%20Paleoclimatol%20-%202022%20-%20Zhang%20-%20Early%20Eocene%20Ocean%20Meridional%20Overturning%20Circulation%20The%20Roles%20of.pdf; https://doi.org/10.1029/2021pa004329

International audience Here, we compare the ocean overturning circulation of the early Eocene (47-56 Ma) in eight coupled climate model simulations from the Deep-Time Model Intercomparison Project (DeepMIP) and investigate the causes of the observed inter-model spread. The most common global meridional overturning circulation (MOC) feature of these simulations is the anticlockwise bottom cell, fed by sinking in the Southern Ocean. In the North Pacific, one model (GFDL) displays strong deepwater formation and one model (CESM) shows weak deepwater formation, while in the Atlantic two models show signs of weak intermediate water formation (MIROC and NorESM). The location of the Southern Ocean deepwater formation sites varies among models and relates to small differences in model geometry of the Southern Ocean gateways. Globally, convection occurs in the basins with smallest local freshwater gain from the atmosphere. The global MOC is insensitive to atmospheric CO$_2$ concentrations from 1× (i.e., 280 ppm) to 3× (840 ppm) pre-industrial levels. Only two models have simulations with higher CO$_2$ (i.e., CESM and GFDL) and these show divergent responses, with a collapsed and active MOC, respectively, possibly due to differences in spin-up conditions. Combining the multiple model results with available proxy data on abyssal ocean circulation highlights that strong Southern Hemisphere-driven overturning is the most likely feature of the early Eocene. In the North Atlantic, unlike the present day, neither model results nor proxy data suggest deepwater formation in the open ocean during the early Eocene, while the evidence for deepwater formation in the North Pacific remains inconclusive