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II. PHYSICAL ATTRIBUTES OF THE 

 ANTARCTIC MARINE ECOSYSTEM 



Antarctica is surrounded by the three contiguous basins 

 of the Pacific, Atlantic, and Indian Oceans. These oceans 

 lose their surface identity within the Antarctic Convergence, 

 a region bounded roughly within 60° s, and 55° S. latitude. 

 In this paper, the Antarctic Convergence shall represent the 

 northern limit of the Southern (or Antarctic) Ocean; its 

 southern limit is the Antarctic coast. Figures 1 and 2 are 

 maps of the area and include the statistical zones used by 

 the Food and Agricultural Organization (FAO) for fisheries 

 purposes. Although primarily a surface phenomenon, the 

 Convergence is nevertheless a boundary delineating distinctly 

 different faunal zones. 



The deeper ocean layers are continuous with the major 

 ocean basins to the north. The Campbell Plateau south of 

 New Zealand, the Kerguelen Jaussberg Ridge, the Atlantic- 

 Indian Rise, and the Scotia Arc are major topographical 

 regions extending into the Southern Ocean from northern 

 areas. Circulation of Southern Ocean water masses is channeled 

 and constricted by bottom bathymetry and the topography of 

 these features. 



A. Major Water Masses and Circulation Patterns 



Three major water masses surround the continent: Antarctic 

 Surface Water, Warm Deep Layer, and Antarctic Bottom Water 

 (Figure 3). The Warm Deep Layer is a highly saline, low- 

 oxygenated, water mass which orginates in the major oceans 

 well to the north (Everson, 1977; Gordon and Goldberg, 

 1970) . It flows south and begins to upwell when it nears 

 the continent. As it reaches near-surface layers, it is 

 split into two different water masses due to the sea/air 

 exchange of heat and water. One mass remains near the 

 surface (Antarctic Surface Water) ; the other sinks to the 

 sea floor contributing to the Antarctic Bottom Water. 



Antarctic Surface Water, which also incorporates fresh 

 water from melting ice and snow, flows northerly until it 

 reaches the Antarctic Convergence and sinks beneath the 

 Subantarctic Surface Water (Everson, 1977). This relatively 

 stationary zone rarely deviates more than 160 km north or 

 south. The mixture of Antarctic and subantarctic waters is 

 reflected by temperature changes ranging to 4° C (Kort, 

 1968) . North of the Convergence, the Antarctic Surface 

 Water becomes Subantarctic Intermediate Water, influencing 

 most of the oceans of the southern hemisphere, but eventually 

 returning south when it is altered by heat flux through the 

 sea floor and across thermoclines (Gordon and Goldberg, 

 1970) . 



