The global ocean overturning circulation plays a central role in climate and climate variability bystoring and transporting heat, fresh water, carbon and nutrients around the world ocean. Whilethe primary site of surface water subduction into ocean interior in the North Atlantic is wellstudied and understood, the return pathway and the dominant physical processes by whichdeep waters return to the surface in the Southern Ocean to close the meridional overturningcirculation is still not well known. Yet, the deep water upwelling in the Southern Ocean is offundamental importance for climate, since the upwelled waters control the rate of ocean heatand carbon uptake from the atmosphere, and supply of nutrients for the global thermocline. Wepropose to provide a three-dimensional quantitative estimates of water masses that comprisethe returning portion of the overturning circulation and physical processes involved using theresults of a data assimilating ocean circulation model.