All of the ocean basins are connected in an overturning circulation from regions where waters sink to where waters rise. We usually describe these based on both (i) maps of the origin and apparent fate of property extremes, for instance high and low salinity, or oxygen, or nutrients, and (ii) calculations of north-south transports of ocean waters across full ocean basins, based on an assumption of geostrophic flow, and then a diagnosis of how the ‘meridional’ transports must connect vertically. But we can also look at this in the very largest global scale, and see that there is a much larger-scale, non-geostrophic forcing that drives these flows. The direction of the flows is largely controlled by the ocean’s salinity distribution, and therefore by the differences in precipitation-evaporation and river runoff between large regions of the ocean.