116 U.S. NATIONAL MUSEUM BULLETIN 291 



at densities greater than sigma-t= 27.75, and eleven captures are located 

 at densities greater than sigma-t= 27.80. One capture lies within the 

 zone of oxygen minimum and the rest lie deeper than the layer of 

 minimum oxygen, mostly at values between 4.25 ml/L and 4.60 ml/L. 

 In summary, the major portion of the captures (and specimens) 

 came from water characterized by temperatures between 1° and 2° C, 

 by salinities in the maximum range, by high densities, and by moder- 

 ate oxygen values below the oxygen minimum layer. 



75" West Longitude; 34" to 67" South Latitudes 



The 75 °W sections extend from 67 °S in the Bellingshausen Sea to 

 34° S off Valparaiso, Chile. The sections transect the western end of 

 the Drake Passage and extend northward in the Peru Current. The 

 temperature section (fig. 29) shows the Antarctic Convergence as a 

 series of vertical isotherms between 59° and 60°S. The 2.5° C isotherm 

 drops steeply from the convergence zone to 1500 m, tapers to 2000 m 

 at 55°S, and extends northward in the Peru Current between 2100 m 

 and 2250 m. North of 52°S the 3° and 4° isotherms remain at about 

 1250 m and 800 m respectively, and south of this latitude they rise 

 to the surface in the convergence zone. The 2° isotherm outlines a long 

 wedge of water that protrudes southward from the convergence at 

 depths between 350 m and 750 m; it reaches just beyond 66° S before 

 it turns northward gradually increasing in depth to about 2500 m at 

 55°S. In the Peru Current the 2° isotherm lies at about 2200 m. The 

 1.5° and 1° isotherms extend from the surface south of the con- 

 vergence to depths greater than 3000 m at 59° to 62° S. A large por- 

 tion of the Antarctic Circumpolar Water in this region is between 

 1.5° and 2.5° C. 



The salinity section (fig. 30) shows the isohalines descending ir- 

 regularly from near the surface at 67°S to middle depths in the Peru 

 Current. The slopes of the isohalines are steepest under the zone of 

 the convergence. The 34.60%o isohaline drops from 300 m at 67° S 

 to 2000 m at 55°S, then passes northward at about 1800 m. The large 

 core of maximum salinity of 34.72%o envelops two smaller cores of 

 34.73%o and 34.74%o. The salinity maximum lies between 1000 m 

 and 2500 m and is shallowest in the southern portion (62° to 65°- 

 30'S) and deepest in the northern segment (62° to 59°S). 



The density is uniformly high at depths of maximum salinity 

 values and low temperature values (fig. 30). The isopleth of sigma- 

 t=27.75 nearly parallels the 34.70%o isohaline and the 2° isotherm. 

 The distribution of oxygen (fig. 29) shows a decrease in concentra- 

 tion toward the north at equal depths. The oxygen minimum value 

 at 65°S is 4.20 ml/L at 600 m and the layer of low oxygen concentra- 

 tion is roughly 500-1000 m. At 62°S the lowest value is 4.05 ml/L 



