Antarctic Intermediate Water (AAIW) is a type of water mass in the Southern Ocean thought to originate mainly through convective overturning of surface waters west of South America during winter, after which this water mass is injected into the subtropical gyre and fills the southern subtropics and tropics from the east.

Antarctic Intermediate Water. Source: Woods Hole Oceanographic Institute

In the Atlantic Ocean, the densest SAMW found in the Subantarctic Zone between the Subantarctic Front and the Subtropical Front is thought to be the primary precursor to AAIW, although some postulate substantial input across the Subantarctic Front. The AAIW in the South Atlantic originates from a surface region of the circumpolar layer, especially in the northern Drake Passage and the Falkland Current loop. AAIW from the Indian Ocean is added to the Atlantic AAIW via  Agulhas Current  leakage. The AAIW is recognized by a subsurface oxygen maximum and a salinity minimum north of about 50 degrees S, although the oxygen maximum becomes weak north of 15 degrees S. The oxygen maximum is found at a slightly lower density than the salinity minimum.

The salinity minimum is found at about 300 m near the Subantarctic Front at around 45^oS, descends northward to 900 m at 30^oS near the subtropical gyre center, and rises again to 700 m at the equator. The AAIW spreads to the North Atlantic, identified by a salinity minimum near the equator at a σ_θ value of about 27.3. This minimum has been found to 24 degrees N, although traces of AAIW can be followed as far north as 60 degrees N. AAIW is characterized by a temperature near 2.2 degrees C and a salinity around 33.8 near its formation region, but erodes by the time it reaches the Subtropical Front to values closer to 3 degrees C and 34.3.

See Also

• Agulhas Current
• Antarctica
• Antarctica Collection on the Encyclopedia of Earth

Further Reading

• Physical Oceanography Index
• Antarctica: The Frozen Continent], Woods Hole Oceanographic Institute (accessed March, 29. 2010)
• A. R. Piola and D. T. Georgi. Circumpolar properties of Antarctic Intermediate Water and Subantarctic Mode Water. Deep-Sea Res., 29:687–711, 1981.
• III Whitworth, Thomas and Worth D. Nowlin Jr. Water masses and currents of the Southern Ocean at the Greenwich Meridian. JGR, 92:6462–6476, 1987.
• M. Tsuchiya. Circulation of the Antarctic Intermediate Water in the North Atlantic Ocean. J. Mar. Res., 47:747–755, 1989.
• Matthias Tomczak and J. Stuart Godfrey. Regional Oceanography: An Introduction. Pergamon, 1994.
• O. Boebel, C. Schmid, and W. Zenk. Flow and recirculation of Antarctic Intermediate Water across the Rio Grande Rise. JGR, 102:20,967–20,986, 1997.
• C. Schmid, G. Siedler, and W. Zenk. Dynamics of intermediate water circulation in the subtropical South Atlantic. JPO, 30:3191–3211, 2000.