Antarctic Intermediate Water in the South Atlantic

Abstract

Maps of the Antarctic Intermediate Water (AAIW) in the Atlantic, and on a global isopycnal which intersects the AAIW in the south, show the location and properties of the salinity and oxygen extrema associated with the AAIW, and the likely sources of AAIW. These are primarily the surface waters in the southeastern Pacific, which produce the South Pacific AAIW, and surface waters in northern Drake Passage and the Falkland Current loop, which produce the South Atlantic AAIW. This latter source is the primary one for AAIW of the Indian Ocean as well. Winter surface properties and annual-averaged Ekman pumping and S verdrup transport for the southern hemisphere suggest that the formation density of the AAIW is the highest density which can be subducted in the South Pacific. The higher density of AAIW in the South Atlantic may result from more complex processes. The connection between the subtropical gyres of the Atlantic and Indian and between the Indian and Pacific Oceans contributes to modification of AAIW as it spreads tortuously northward around the subtropical gyres. Potential vorticity and AAIW salinity and oxygen illustrate the near barrier between the subtropical and tropical regimes, at about 20°to 25°north and south of the equator. Communication between the regimes is primarily through the western boundary currents.