Size matters: another reason why the Atlantic is saltier than the Pacific

Idealized numerical experiments are performed with an ocean-only
circulation forced by wind-stress, surface temperature and freshwater
flux, all independent of longitude, in a domain consisting of two
basins, differing only in their widths, which are connected by a
circumpolar channel at the south and. These experiments show that a
spontaneous asymmetry in the latitudinal distribution of surface
salinity develops, which favors salinification of the narrow basin
over the wide basin. This salinification induces a stable pole-to-pole
overturning in the narrow basin, maintained by the salt-advection
feedback. Pole-to-pole overturning in the wide basin does not occur
for zonally-symmetric forcing, but can be induced by reducing the
precipitation over the northern end of the wide basin. The preference
for sinking at the northern end of the narrow basin over sinking in
the wide basin is due to two compounding processes: a larger
overturning velocity associated with narrow-basin sinking, and a
smaller gyral velocity, which is always found in the narrow basin
compared to the wide basin. Together, these differences in salt
advection favor sinking in the narrow basin.