Oceanic hindcast simulations at high resolution suggest that the Atlantic MOC is bistable

Julie Deshayes (1, 2) , Anne-Marie Tréguier (1) , Bernard Barnier (3) , Albanne Lecointre (4) , Julien Le Sommer (3) , Jean-Marc Molines (3) , Thierry Penduff (3) , Romain Bourdallé-Badie (5) , Yann Drillet (5) , Gilles Garric (5) , Rachid Benshila (6) , Gurvan Madec (6) , Arne Biastoch (7) , Claus W. Böning (7) , Markus Scheinert (7) , Andrew C. Coward (8) , Joël J.-M. Hirschi (8)

1 LPO - Laboratoire de physique des océans
2 LMI ICEMASA
3 LGGE - Laboratoire de glaciologie et géophysique de l'environnement
4 LEGI - Laboratoire des Écoulements Géophysiques et Industriels [Grenoble]
5 Mercator Océan
6 NEMO R&D - Nucleus for European Modeling of the Ocean
7 GEOMAR - Helmholtz Centre for Ocean Research [Kiel]
8 NOC - National Oceanography Centre [Southampton]

All climate models predict a freshening of the North Atlantic at high latitude that may induce an abrupt change of the Atlantic Meridional Overturning Circulation (hereafter AMOC) if it resides in the bistable regime, where both a strong and a weak state coexist. The latter remains uncertain as there is no consensus among observations and ocean reanalyses, where the AMOC is bistable, versus most climate models that reproduce a mono-stable strong AMOC. A series of four hindcast simulations of the global ocean at 1/12° resolution, which is presently unique, are used to diagnose freshwater transport by the AMOC in the South Atlantic, an indicator of AMOC bistability. In all simulations, the AMOC resides in the bistable regime: it exports freshwater southward in the South Atlantic, implying a positive salt advection feedback that would act to amplify a decreasing trend in subarctic deep water formation as projected in climate scenarios.

Mots clés: AMOC; freshwater; bistability; modeling

Domaines: Géophysique [physics.geo-ph]; Géophysique [physics.geo-ph]; Milieux et Changements globaux; Océanographie

Julie Deshayes, Anne-Marie Tréguier, Bernard Barnier, Albanne Lecointre, Julien Le Sommer, et al.. Oceanic hindcast simulations at high resolution suggest that the Atlantic MOC is bistable. Geophysical Research Letters, 2013, 40, pp.3069-3073. ⟨10.1002/GRL.50534⟩. ⟨hal-00872044⟩