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V. DESCRIPTION OF ENVIRONMENT 



A. Physical Environment 



Surrounding the Antarctic continent is a ring of 

 ocean contiguous with the Atlantic, Pacific and Indian 

 Oceans to the north. The Antarctic Convergence is the 

 northern boundary of Antarctic waters. Waters north of 

 the Convergence are subantarctic . The average ocean area 

 south of the Convergence is 38 x 10^ km^ (El-Sayed, in 

 press) . 



1. Antarctic Convergence 



The Antarctic Convergence is a boundary between 

 different water masses. South of the Convergence water 

 surface temperature drops 2 to 3°C. The exact geographic 

 location of the Convergence varies with changing thermo- 

 cline and wind stress conditions, but it can be located 

 with temperature and salinity measurements. 



The Antarctic Convergence also known as the Antarctic 

 Polar Front Zone, is not a very sharp boundary, but actually 

 is a transitional zone between water masses. It is a charac- 

 teristic of surface water masses, having a depth of up to 

 600 meters. The deep northward flowing Antarctic bottom 

 water flows underneath the Convergence (Gordon, 1971) . The 

 Antarctic Convergence is not a boundary for deep living 

 organisms such as bathypelagic fishes. 



A map of the southern ocean showing the position of the 

 Convergence and other features is given in Figure 1. The 

 Convergence lies approximately along 50 S latitude in the 

 Indian and Atlantic Ocean sectors. In the Drake Passage it 

 lies approximately halfway between the tip of the Antarctic 

 peninsula and the tip of South America. In the Pacific 

 sector it lies approximately between 55°S and 60°S latitude 

 (Mackintosh, 1972) . The Convergence is a physical oceano- 

 graphic boundary. It is also a faunal boundary. Biological 

 communities south of the Convergence are distinct from those 

 north of it (Marr, 1962; Hasle, 1968). 



2. Currents 



Surface currents flow latitudinally in the southern 

 ocean. Near the continent water flows toward the west and 

 is known as the East Wind Drift. North of approximately 

 60OS latitude water flows toward the east and is known as 

 the West Wind Drift or the Circumpolar Current. There is a 



