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

Yurui Zhang (1) , Agatha M. de Boer (2) , Daniel J. Lunt (3) , David K. Hutchinson (2) , Phoebe Ross (4) , Tina Flierdt (5) , Philip Sexton (6) , Helen Coxall (2) , Sebastian Steinig (3) , Jean-Baptiste Ladant (7, 8) , Jiang Zhu (9) , Yannick Donnadieu (10) , Zhongshi Zhang (11) , Wing‐le Chan (12) , Ayako Abe‐ouchi (12) , Igor Niezgodzki (13, 14) , Gerrit Lohmann (13) , Gregor Knorr (13) , Christopher J. Poulsen (15) , Matt Huber (16)

1 MEL - State Key Laboratory of Marine Environmental Science
2 Bolin Centre for Climate Research
3 School of Geographical Sciences [Bristol]
4 CCRC - Climate Change Research Centre [Sydney]
5 Department of Earth Science and Engineering [Imperial College London]
6 OU - The Open University [Milton Keynes]
7 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
8 CLIM - Modélisation du climat
9 NCAR - National Center for Atmospheric Research [Boulder]
10 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement
11 CUG - China University of Geosciences [Wuhan]
12 AORI - Atmosphere and Ocean Research Institute [Kashiwa-shi]
13 Alfred Wegener Institute, Bremerhaven
14 UWr - Institute of Geological Sciences [Wrocław]
15 University of Michigan [Ann Arbor]
16 EAPS - Department of Earth, Atmospheric, and Planetary Sciences [West Lafayette]

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

Domaines: Océan, Atmosphère; Interfaces continentales, environnement

Yurui Zhang, Agatha M. de Boer, Daniel J. Lunt, David K. Hutchinson, Phoebe Ross, et al.. Early Eocene Ocean meridional overturning circulation: The roles of atmospheric forcing and strait geometry. Paleoceanography and Paleoclimatology, 2022, 37 (3), pp.e2021PA004329. ⟨10.1029/2021pa004329⟩. ⟨hal-03598897⟩