Early Eocene ocean meridional overturning circulation: the roles of atmospheric forcing and strait geometry

Yurui Zhang, Agatha M. Boer, Daniel J. Lunt, David K. Hutchinson, Phoebe Ross, Tina Flierdt, Philip Sexton, Helen K. Coxall, Sebastian Steinig, Jean‐baptiste Ladant, Jiang Zhu, Yannick Donnadieu, Zhongshi Zhang, Wing‐le Chan, Ayako Abe‐ouchi, Igor Niezgodzki, Gerrit Lohmann, Gregor Knorr, Christopher J. Poulsen, Matt Huber

Research output: Contribution to journalArticle (Academic Journal)peer-review

11 Citations (Scopus)

Abstract

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 CO2 concentrations from 1× (i.e., 280 ppm) to 3× (840 ppm) pre-industrial levels. Only two models have simulations with higher CO2 (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.
Original languageEnglish
Article numbere2021PA004329
JournalPaleoceanography and Paleoclimatology
Volume37
Issue number3
Early online date19 Feb 2022
DOIs
Publication statusPublished - 19 Feb 2022

Bibliographical note

Funding Information:
The authors acknowledge valuable contributions from anonymous reviewers and pertinent suggestions from the Editor and associated Editor that have clarified and improved the manuscript. The authors would like to thank Thierry Huck for discussions in the early stage of the analysis. YZ was supported by the Fundamental Research Funds for the Central University (Grant no. 20720210079). AdB acknowledges funding from Swedish Research Council projects 2016‐03912 and 2020‐04791. DJL and SS acknowledge NERC Grant NE/P01903X/1. DKH acknowledges funding from FORMAS Grant 2018‐01621, and their GFDL model simulations were performed by resources provided by the Swedish National Infrastructure for Computing (SNIC) at the National Supercomputer Centre (NSC), partially funded by the Swedish Research Council through grant agreement 2018‐05973. PR and TvdF acknowledge funding from NERC Grant NE/P019080/1. PS was supported by Natural Environment Research Council (NERC) Grant NE/P019331/1. HKC was supported by the Swedish Research Council (VR) Grant DNR 2014‐4153. J‐BL and YD acknowledge GENCI for providing access to the HPC resources of TGCC through allocation no. 2019‐A0050102212, with which IPSL simulations were performed. JZ and CP acknowledge the support of the Heising‐Simons Foundation (Grant nos. 2016‐05 and 2016‐12) and National Science Foundation (Grant no. 2002397), as well as computational resources provided by the Computational and Information Systems Laboratory at the National Center for Atmospheric Research, which is a major facility sponsored by the NSF under Cooperative Agreement 1852977. WLC and Ayako Abe‐Ouchi acknowledge funding from JSPS KAKENHI (Grant no. 17H06104) and MEXT KAKENHI (Grant no. 17H06323), and are grateful to JAMSTEC for use of the Earth Simulator. Matt Huber acknowledges support from NSF Grant 1842059.

Funding Information:
The authors acknowledge valuable contributions from anonymous reviewers and pertinent suggestions from the Editor and associated Editor that have clarified and improved the manuscript. The authors would like to thank Thierry Huck for discussions in the early stage of the analysis. YZ was supported by the Fundamental Research Funds for the Central University (Grant no. 20720210079). AdB acknowledges funding from Swedish Research Council projects 2016-03912 and 2020-04791. DJL and SS acknowledge NERC Grant NE/P01903X/1. DKH acknowledges funding from FORMAS Grant 2018-01621, and their GFDL model simulations were performed by resources provided by the Swedish National Infrastructure for Computing (SNIC) at the National Supercomputer Centre (NSC), partially funded by the Swedish Research Council through grant agreement 2018-05973. PR and TvdF acknowledge funding from NERC Grant NE/P019080/1. PS was supported by Natural Environment Research Council (NERC) Grant NE/P019331/1. HKC was supported by the Swedish Research Council (VR) Grant DNR 2014-4153. J-BL and YD acknowledge GENCI for providing access to the HPC resources of TGCC through allocation no. 2019-A0050102212, with which IPSL simulations were performed. JZ and CP acknowledge the support of the Heising-Simons Foundation (Grant nos. 2016-05 and 2016-12) and National Science Foundation (Grant no. 2002397), as well as computational resources provided by the Computational and Information Systems Laboratory at the National Center for Atmospheric Research, which is a major facility sponsored by the NSF under Cooperative Agreement 1852977. WLC and Ayako Abe-Ouchi acknowledge funding from JSPS KAKENHI (Grant no. 17H06104) and MEXT KAKENHI (Grant no. 17H06323), and are grateful to JAMSTEC for use of the Earth Simulator. Matt Huber acknowledges support from NSF Grant 1842059.

Publisher Copyright:
© 2022. American Geophysical Union. All Rights Reserved.

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