34 



CHEMICAL RESULTS OF LAST CRUISE OF CARNEGIE 



southern part of the section are weak and in a westerly 

 direction. The University of Washington station is prob- 

 ably in the narrow westerly current close to the Aleutian 

 Islands. The convection layer is 40 meters thick at sta- 

 tion Ba. At most of the other stations of the section it 

 is rather uniformly about 20 meters thick but widens 

 toward the south to 95 meters at station Bo, and narrows 

 to 75 meters at station Bp. 



The oxygen content of the surface water in the north- 

 ern part of the section is over 6 ml per liter; at station 

 Bf it drops to below 6 ml per liter, and from station Bk 

 to the south end of the section it is between 4 and 5 ml 

 per liter. This decrease in the oxygen content of the 

 surface water from north to south is to be expected be- 

 cause of the increasing temperatures and the decreasing 

 solubility of oxygen. 



As regards the subsurface distribution of oxygen in 

 this section there is a close resemblance to the distri- 

 bution in the regions investigated by the Carnegie in the 

 northeastern Pacific (see sections VII, XIV, and XV). 

 There is a layer of maximum oxygen content throughout 

 the section in the upper 100 meters at all stations ex- 

 cept at the extreme south where it drops to 150 meters. 

 In the colder water to the north this layer contains more 

 than 7 ml per liter of oxygen but southward it decreases 

 to less than 6 ml per liter. 



The transition zone is nearest the surface at the 

 northernmost Bushnell stations where its lower limit is 

 above 300 meters. At the station (5055-17220) to the 

 north it extends to 425 meters. Proceeding southward, 

 the transition zone sinks and expands, reaching its low- 

 est depth and maximum expansion at station Bi, latitude 

 36° 52' north, where it extends from 500 to 900 meters. 

 South of this station it contracts somewhat and rises. 

 At Carnegie station 140 it lies between 440 and 650 me- 

 ters. 



Throughout the section there is a well-developea 

 layer of minimum oxygen content. Although the level of 

 the axis of this minim\mi falls and rises from north to 

 south in B manner paralleling that of the transition zone, 

 the thickness of the layer poor in oxygen decreases con- 

 tinuously from the northernmost Bushnell station (Ba) 

 southward. At station Ba there is a layer of water 1210 

 meters thick, from 280 to 1490 meters below the sur- 

 face, in which the oxygen content is less than 1 ml per 

 liter. At station Bh, where the layer that is poor in oxy- 

 gen reached its greatest depth below the surface, its 

 thickness was 1080 meters, extending from 820 to 1900 

 meters below the surface. South of this station this 

 layer rises and narrows more rapidly. At Carnegie sta- 

 tion 140 the layer with less than 1 ml per liter of oxygen 

 is only 400 meters thick, lying between 650 and 1050 me- 

 ters below the surface. Water extremely deficient in 

 oxygen, represented by concentrations less than 0.5 ml 

 per liter, occurred in two parts of the section- -toward 

 the north at stations Ba and Bb, and toward the south be- 

 tween stations Bh and Bo. 



Below the layer of minimum oxygen there is a fairly 

 regular increase in the oxygen content with depth at all 

 stations. At 3500 meters there is somewhat more than 

 3 ml per liter of oxygen. In the deep water there is a 

 considerable decrease in the oxygen content from the 

 south northward to station Bh, latitude 39° 51' north, but 

 from here northward there is an increase, although the 

 concentrations in the northern part of the section are 

 never as great as those in the extreme southern part. 

 Thus, at the 2000-meter level the oxygen content, which 

 at Carnegie station 140 is 2.25 ml per liter, decreases 

 to 1.15 at station Bh, and then increases northward to 

 1.65 ml per liter at station Ba, and 1.55 at station 5055- 

 17220. Similar conditions were found at the 300-meter 

 level. 



HANNIBAL AND PIONEER SECTIONS 



The pxygen data obtained by R. H. Fleming on board 

 the U. S. S. Hannibal in the Gulf of Panama and off the 

 coasts of Panama and Costa Rica in 1933 are in excellent 

 agreement with the data obtained by Schmidt (1925) in 

 the Gulf of Panama. In connection with the regional dis- 

 tribution of oxygen it is of importance to note that the 

 deep water at the Hannibal stations contained more oxy- 



gen than did the Carnegie stations farther north. 



At the live stations occupied by the Pioneer . Revelle 

 found the distribution of oxygen to be very similar to 

 that found by the Carnegie at station 130 which was oc- 

 cupied four years earlier and several hundred miles 

 farther north. 



REGIONAL DISTRIBUTION 



Surface Layer 



Revelle's data, obtained on board the U.S.S. Bush - 

 nell , show that north of latitude 40° north at the surface 

 the water was supersaturated with oxygen. Farther 

 south the relative concentration of oxygen at the surface 

 was somewhat less. At most stations between latitudes 

 40° and 20° north the oxygen content of the surface 

 water was just under saturation, the relative concentra- 

 tion varying from 96 to 101 per cent of saturation at all 

 stations except station Bk, where it was 90 per cent. At 

 the next group of stations, between the equator and lati- 

 tude 20° north, the quantity of oxygen at the surface was 

 still less. At the five stations farthest south, latitudes 

 6° to 13° south, the relative concentration of oxygen 

 ranged from 78 to 89 per cent of saturation. There is 



thus a decrease in the dissolved oxygen content at the 

 surface from north to south, not only in the absolute 

 quantity, which is to be expected because of the temper- 

 ature increase, but also in the percentage of saturation. 

 This probably reflects a variation in the amount of phyto- 

 plankton from north to south, except at the southernmost 

 group of stations where the unusually low oxygen content 

 indicates that the water at the surface had been mixed 

 with subsurface water of a normally low oxygen content. 

 This is further indicated by the fact that at these stations 

 the phosphate content at the surface was relatively high. 



In at least part of the convection zone, the oxygen 

 content was the same as at the surface. At stations 

 north of latitude 20° north surface values extended to a 

 depth varying from 10 to 15 meters, but seldom to more 

 than 5 meters at stations farther south. The position of 



