Séminaire
The ventilation of the abyssal ocean and the associated oceanic carbon and heat storage occurs to a large extent through overturning circulations. In this seminar, I will illustrate with the cases of the Atlantic and Mediterranean overturning circulations how the momentum and vorticity balances impose strong constraints on the flow. The momentum balance induces a mostly geostrophic horizontal transport, whereas vorticity dynamics require a mostly ageostrophic vertical transport to close those overturning cells. Starting with the momentum constraint, I will propose a general expression of the geostrophic Atlantic Meridional Overturning Circulation (AMOC) as a form stress. I will then illustrate how this form stress can be simplified into a
density anomaly at both zonal boundaries with the case of CNRM-CM6 and IPSL-CM6's strong centennial AMOC variabilities. Lastly, I will illustrate the vorticity constraint on the sinking of the Mediterranean Overturning Circulation. We have modelling and
observational evidence that this downwelling occurs within 50km of the boundary, away from convective regions. The vorticity balance of an eddying (1/12°) regional NEMO configuration confirms that only interactions with the topography allow for the necessary sinking to close the overturning circulation.
juliette.mignot@locean-ipsl.upmc.fr