BATHYPELAGIC SQUID BATHYTEUTHIS 97 



The Antarctic Convergence is a major fundamental boundary zone; 

 it is continuous all around the continent and its location between 50° 

 and 60° south latitudes depends upon land masses, oceanographic 

 conditions and bottom topography. Land masses that impinge from 

 the north create a relatively narrow channel and force the convergence 

 southward toward the Antarctic Continent. This is particularly the 

 case south of the Australia, Tasmania, New Zealand region and be- 

 tween South America and the Antarctic Peninsula. Bottom topog- 

 raphy is important to the location of the convergence. In regions 

 approaching ridges or rises the convergence is deflected to the north ; 

 downstream of the shoal areas the convergence moves southward. The 

 sharp bends in the convergence are imposed by such bottom features 

 as the Pacific-Antarctic Ridge, the South Antilles Arc, and the Ker- 

 guelen and Macquarie Ridges. Position of the convergence is marked 

 at the surface by a steep temperature gradient that ranges from l°-3° C 

 in winter and 3°-8° C in summer (Mackintosh, 1946) . Just beneath the 

 surface convergence zone the northward flowing Antarctic Upper 

 Water sinks beneath the southward moving Subantarctic Surface 

 "Water. In subsurface waters Deacon (1937) considered that the con- 

 vergence is coincident with the area in which warm Deep Water rises 

 above Antarctic Bottom Water. 



The water masses in the Antarctic Ocean are cliaracterized by the 

 temperature-salinity relationships. The Antarctic Surface Water 

 occurs as a thin sheet of nearly homogeneous water over the entire 

 Antarctic region; it has low temperatures, between —1.8° and 1.0° C, 

 and low salinities, between 34.0%o and 34.51%o. In winter the tempera- 

 ture is lowest and tlie salinity is highest due to reduced solar radiation 

 and ice formation. The reverse conditions prevail in summer. The 

 mixed layer extends from 50 to 200 m depending primarily upon the 

 wind conditions over the sea surface. It is deepest near the convergence 

 and the continent and shallowest near the divergence (ca 65°-70°S) 

 between the east and the west wind drifts (Deacon, 1963). Over the 

 continental shelf, particularly in the Weddell Sea and probably in the 

 Ross Sea, the very cold, saline water (-1.95°C, 34.70%o) resuhing 

 from ice formation may extend to the bottom and contribute to the 

 formation of bottom water (see below). Immediately beneath the sur- 

 face layer is a transition zone that increases rapidly to over 2° C and 

 gradually to over 34.5%o. 



Antarctic Circumpolar Water lies below the Antarctic Surface Wa- 

 ter and is characterized by temperatures between 0.5° and 2.0° C and 

 salinities slightly above 34.70%o. Maximum temperatures occur at 

 500-600 m and maximum salinities slightly deeper at 700-1300 m. 

 The Antarctic Circumpolar Water is an extremely uniform water 



