Table 5. — Summary of oblique 1-m. net hauls at fronts 2 and A. Counts (from aliquots) have been 

 standardized to full sample size and to lO-'m.^ of water strained. w=warm side; c = cool side 



Organisms 



Station 



2.3 (w) 



2.2 



4.3 (w) 



■4.4 (c) 



Volume of catch in ml. per lO^m.^ 

 Counts of organisms : 



Copepods 



Chaetognaths 



Euphaxisiids . , 



Siphonophores (none colonial).. 



Salps 



Larvaceans 



Heteropods 



Foraminifera 



Ostracods 



Doliolids 



35 



11,325 



2,662 



332 



l,<ilO 



'438 

 294 



120 



12,116 



4,025 



1,092 



1,092 



789 



445 



263 



89 



8,334 

 2,389 

 1,152 



654 



441 



284 



79 



22,720 



844 



760 



3,646 



1,452 

 371 



found only on one side or the other. A macro- 

 scopic inspection of the remainders of the 

 samples confirmed this exclusiveness. 



The ship's track at front 4 was planned to 

 reveal both the general orientation of the front 

 and its rate of advance (fig. 36). The track 

 duplicated itself to some extent; the first part 

 was from 0330 hours to 0707 hours, and the 

 second was from 0828 hours to 1900 hours. 

 The part 0707-0828 hours connects the two 

 but is of no use in plotting the isotherms (fig. 

 36). Neither the general form nor the rate of 

 advance was satisfactorily determined. On the 

 first part, the front was in the form of a loop 

 which may have become muchchanged, judging 

 from the intersections of the 20° and 20.5° C. 

 isotherm with the tract shortly after 0707 

 hours. (This assumes no serious error in the 

 plotting of the track; e.g., through dead-reckon- 

 ing navigation.) On the second part the front 

 appears to have been oriented roughly north- 

 east- -south-west, but such an alignment also 

 would arise if the front were oriented east- 

 west and were moving north; in that event, 

 the spurious alignment (NE-SW) would be due 

 only to time lag between successive crossings 

 of the northward-moving front. Both possi- 

 bilities could co-exist, of course. If the front 

 were moving north, its approximate speed 

 would be given by the difference in latitude 

 north of the 20° C. isotherm at about 0835 

 and 1715 hours; that is, about 4 miles in nearly 

 8 1/2 hours --approximately half a knot. 



In view of the short time available, and the 

 belief that this front would be comparable with 

 front 2, no BT pass was made, unfortunately. 

 As at front 2, hydrocasts were somewhat dis- 

 tant from the front, being about 20 km. apart. 

 The restrictions on the discussion of the prop- 

 erty profiles applied to front 2 also apply here. 



47 



The isotherms in the upper 100 m. deepen 

 towards the warm side, as they did at front 2. 

 There was a thermocline at 50-60 m. (cool 

 side) to 70-90 m. (warm side). 



The salinity profile (as at front 2) indicates 

 a complicated salinity structure; this is shown 

 by the T-S curves (fig. 37). 



The T-S curve for the cool side is reason- 

 ably typical of California Current water in that 

 area (marked salinity minimum), with some 

 indication, by the low surface salinity relative 

 to that of the general area, that the surface 

 waters were upwelled. The T-S curve for the 

 warm side shows a surface salinity consistent 

 with that of California Current water in that 

 area, but, like the T-S curve of the cool side 

 at front 2, it also shows an anomaly: a marked 

 salinity minimum was not present. One pos- 

 sible cause is that the warm water of this 

 front was a mixture of California Current 

 water and saltier, warmer water in the region 

 (i.e., Gulf or equatorial Pacific water). If 

 mixing were the cause, however, one might 

 expect not only a small vertical salinity 

 gradient (as is seen: S~34.50/i, in the upper 

 110 m.), but also a small vertical temperature 

 gradient; such is found in the upper 50 m. but 

 not from 50 to 100 m. depth. 



These two T-S curves illustrate the changes 

 that occurred during the 13 days between 

 studies at front 2 and front 4. This was in 

 spite of the superficial similarity. Surface 

 temperatures were: front 2 - 1 9.96° to 21.74° 

 C; front 4-19.34° to 21.00° C, --respective 

 differences of 1.78° and 1.66° C. The surface 

 salinities were: front 2-34.36 to 34.79 %o; 

 front 4-34.31 to 34.52%„. The decrease from 

 34.79 to 34.52%, during the 13 day interval 

 suggests that low salinity, probably upwelled 

 (note lowered temperature, from 21.74° to 



