122 U.S. NATIONAL MUSEUM BULLETIN 291 



there is similar to that farther west in the Pacific, it is reasonable to 

 assume that the captures below 1800 m occur in and below the oxygen 

 minimum layer. 



To summarize, the majority of captures (and the great majority of 

 specimens) was taken in waters characterized by temperatures less 

 than 2.5° C, salinities greater than 34.60%o (salinity maximums), 

 densities above sigma-t= 27.65, and oxygen concentrations of 3.80 

 ml/L to 4.80 ml/L. The relatively few captures in waters of high 

 temperature and low salinity contained almost exclusively larval and 

 juvenile specimens. By far the greatest number of captures and speci- 

 mens came from the deep waters (below 1000 m) of the Antarctic 

 Circumpolar Water Mass. Just north of the Antarctic Convergence 

 the location of captures in less than 1000 m corresponds to the Ant- 

 arctic Intermediate Water Mass. The plots in the Peru Current shal- 

 lower than 1250 m are also located in Antarctic Intermediate Water. 

 All of the tows in Antarctic Intermediate Water were comprised 

 mostly of larvae and juveniles of B. abyssicola. Captures deeper than 

 1800 m in the Peru Current were made in the Upper Pacific Deep 

 Water Mass. 



115** West Longitude; 55° to 70° South Latitudes 



The sections of oceanographic parameters for 115°W transect the 

 central region of the Pacific Antarctic Basin from 70 °S to 55 °S. The 

 temperature section locates the Antarctic Convergence between 63° 

 and 64°S (fig. 31). The southerly position of the convergence at this 

 longitude is the result of the southward bend imparted to the Antarctic 

 Current as it flows down the slope of the Pacific Antarctic Ridge that 

 lies to the west. 



South of 64° S the water is cold at all depths. The 2° isotherm that 

 lies at the surface in the convergence zone (ca. 60°30'S) swings sharply 

 northward below the surface so that between 100 m and 300 m a tongue 

 of water less than 2° C penetrates as far as 50°30'S. From there the 

 2° isotherm swings southward with increasing depth and reaches its 

 southernmost penetration in 900-1000 m at 64°S before again passing 

 northward with gradually increasing depth. Tlie southward tongue of 

 the 2° isotherm is much less developed than at 75 °W where it pene- 

 trates beyond 66°S at depths between 300 and 800 m. The 2.5° iso- 

 therm lies at 1350 m at 55 °S and ascends to the surface in the con- 

 vergence zone. The 1.5° isotherm lies at 700 m at 70°S and it descends 

 evenly northward and lies at 2950 m at 55°S. 



The isohalines that lie in less than 500 m at 70° S gradually descend 

 and become more widely spaced in lower latitudes (fig. 32). The 

 34.50%o isohaline lies at 200 m at 70°S and descends to 1200 m at 55°S. 



