This salinity minimum, unique to the AAIW, can be recognized throughout the Southern Ocean at depths ranging from 700 to 1200 meters.
Due to vertical mixing at intermediate depths in the Southern Ocean, the salinity slowly rises as it moves northward.
The formation of AAIW can be explained very simply through the Ekman transport process and the divergence and convergence of water masses.
Once the NADW is upwelled to the surface some of it diverges towards Antarctica, gets colder, and sinks back down as Antarctic Bottom Water.
This region is referred to as the Antarctic Convergence Zone/Antarctic Polar Front because of the sharp gradients in both temperature and salinity (esp.
The sinking AAIW becomes sandwiched between the Subantarctic water (above) which is much warmer, but more saline and the NADW (below) which is cold and quite salty.
Because of the difficulty of getting observations in this very treacherous area, this research on Subantarctic mode water mixing theory is still being worked out, but a lot of evidence exists for its inclusion in the formation of AAIW.
[7][8] It is important to note that the biggest source of AAIW formation is just southwest of the southern tip of South America.