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REVIEWS OF GEOPHYSICS, VOL. 45, RG2001, doi:10.1029/2004RG000166, 2007

On the driving processes of the Atlantic meridional overturning circulation

T. Kuhlbrodt

Potsdam Institute for Climate Impact Research, Potsdam, Germany


A. Griesel

Scripps Institution of Oceanography, La Jolla, California, USA


M. Montoya

Departamento Astrofisica y Ciencias de la Atmósfera, Facultad de Ciencias Físicas, Universidad Complutense de Madrid, Madrid, Spain


A. Levermann

Potsdam Institute for Climate Impact Research, Potsdam, Germany


M. Hofmann

Potsdam Institute for Climate Impact Research, Potsdam, Germany


S. Rahmstorf

Potsdam Institute for Climate Impact Research, Potsdam, Germany


Abstract

Because of its relevance for the global climate the Atlantic meridional overturning circulation (AMOC) has been a major research focus for many years. Yet the question of which physical mechanisms ultimately drive the AMOC, in the sense of providing its energy supply, remains a matter of controversy. Here we review both observational data and model results concerning the two main candidates: vertical mixing processes in the ocean's interior and wind-induced Ekman upwelling in the Southern Ocean. In distinction to the energy source we also discuss the role of surface heat and freshwater fluxes, which influence the volume transport of the meridional overturning circulation and shape its spatial circulation pattern without actually supplying energy to the overturning itself in steady state. We conclude that both wind-driven upwelling and vertical mixing are likely contributing to driving the observed circulation. To quantify their respective contributions, future research needs to address some open questions, which we outline.

Received 3 December 2004; accepted 26 October 2006; published 24 April 2007.

Keywords: meridional overturning circulation; thermohaline circulation; diapycnal mixing; wind-driven upwelling.

Index Terms: 4532 Oceanography: Physical: General circulation (1218, 1222); 1635 Global Change: Oceans (1616, 3305, 4215, 4513); 4568 Oceanography: Physical: Turbulence, diffusion, and mixing processes (4490); 4279 Oceanography: General: Upwelling and convergences (4964).

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Citation: Kuhlbrodt, T., A. Griesel, M. Montoya, A. Levermann, M. Hofmann, and S. Rahmstorf (2007), On the driving processes of the Atlantic meridional overturning circulation, Rev. Geophys., 45, RG2001, doi:10.1029/2004RG000166.