Antarctic Intermediate Water (AAIW)

Antarctic Intermediate Water (AAIW) is a cool, low-salinity water mass that fills the intermediate layer of the Southern Hemisphere and tropical oceans near 800 to 1000 meters depth, recognized as a salinity minimum of about 34.2 to 34.4. It forms by wintertime convection in the Subantarctic and near the Polar Front, where Subantarctic Mode Water is converted and subducted equatorward. Temperatures run 3 to 7 degrees Celsius. AAIW is unusual among sinking water masses because its salinity is low rather than high, and it ventilates the intermediate ocean across all three basins.