Atlantic meridional overturning circulation and the Southern Hemisphere supergyre

The ocean's role in climate manifests itself through its high heat capacity, its own rich internal dynamics and its ability to transport vast quantities of heat and freshwater. Of particular interest is the global ocean circulation associated with the Atlantic meridional overturning (AMOC). Because observations are sparse, the detailed global structure of the AMOC remains poorly understood, particularly the pathways along which water returns to the Atlantic to compensate the export of North Atlantic Deep Water (NADW). Here we provide the first quantitative 3-dimensional global view of the AMOC using a Lagrangian reconstruction which integrates hundred of thousands water particle trajectories in an ocean model. The resulting pattern elucidates the role of the wind in structuring the pathways of the AMOC. In particular, the Lagrangian analysis reveals a strong link with the three subtropical gyres of the southern hemisphere (SH), which merge into a "supergyre'' spanning the three ocean basins. The coupling between the upper ocean wind-driven circulation and the overturning in the model suggests that changes in the SH winds can alter the pathways of the AMOC, and therefore the water properties and the associated heat and freshwater transports.