Thermosteric anomaly, S j 



In terms of features the profiles of 8j 

 strongly resennble those of temperature. Off 

 western Lower California the pycnocline is 

 at 100 m. offshore and breaks the surface 

 inshore; it nnay be somewhat stronger near 

 Cape Falso. In the Gulf the pycnocline is 

 strong and shallow, with surface values from 

 400 to 420 cl./ton. Figure 25 shows the dis- 

 tribution of the anomaly between stations 7 

 and 22. As in the temperature and salinity 

 distributions a front exists between stations 

 12 and 14. The undulations in the subsurface 

 density layers east of station 13 correspond 

 very clearly to the various different salinity 

 nodes there. On lines farther south the values 

 at the surface tend to increase, as they do for 

 temperature, and the structures in the density 

 distribution continue to resemble closely those 

 in the temperature distribution. The isanos- 

 teric surfaces chiefly associated with the gross 

 features of the salinity distribution have al- 

 ready been mentioned: 60 to 120 cl./ton--deep 

 salinity minimum; 130 to 180 cl./ton- -deep 

 salinity maximum; 260 to 320 cl./ton--shaIlow 

 salinity minimum; 220 to 260 and 360 to 460 

 cl./ton--high Gulf salinities below and above 

 the shallow salinity minimum. 



Dissolved oxygen 



So far I have assumed that the methods of 

 data collection on the two cruises (6004-B 

 and TO-60-1) with respect to the measure- 

 ment of a property were the same. If any 

 difference exists, it is likely to be most 

 evident in the determination of oxygen, less 

 so in that of salinity, and least in that of 

 temperature. 



In view of its lower temperature and salinity 

 at the surface, one might expect the oxygen 

 content of the California Current Surface 

 Water to be higher than that of the warmer, 

 saltier waters to the south and east. That 

 this is not so may be partially due to the 

 possible differences in method mentioned, 

 but a more obvious explanation is that the up- 

 welled water off Lower California has a low 

 oxygen content and has spread toward the 

 south and southwest. It would normally come, 

 eventually, into equilibrium with the atmos- 

 phere, but at the time it was measured it was 

 only 80 to 90 percent saturated over a large 

 area. 



Measurements of oxygen along line 143 were 

 erroneous. In the profiles along lines 147, 150, 

 and 153 (fig. 26) the chief feature is the 

 "oxycline" that slopes upward and strengthens 

 from west to east, like the thermocline but 

 slightly deeper, especially to the west. The 

 oxygen minimum, shown previously on the 

 corresponding temperature and salinity pro- 



files, is measured by the 0.1 ml./l. isopleth 

 and is restricted, but is less attenuated with 

 decreasing northern latitude. The node of 

 oxygen concentration of I.O ml./l. at about 

 150 m. at station 153.60 corresponds to one 

 of lowered salinity (see fig. 19). 



Across the Gulf (stations 1 to 5) a strong, 

 shallow stratification of oxygen is also present, 

 somewhat deeper, and less marked, than the 

 thermocline. Oxygen content is relatively 

 high--about 115 percent of saturation- -in the 

 thermocline, at about 30 m., from station 2 

 to 3; local phytoplankton activity may be the 

 cause. 



The profile between stations 7 to 22 (fig. 

 27) also shows a strong oxygen gradient 

 comparable to and slightly deeper than the 

 corresponding thermocline. The front between 

 stations 12 and 14 is not obvious from the 

 oxygen distribution, but the depth of the 

 "oxycline" changes relatively sharply at about 

 station 14. The oxygen minimum is attenuated 

 to the west, i.e., toward the California Cur- 

 rent Water. 



The point was made earlier that the oxygen 

 contours had a wavelike form between stations 

 12 and 7 in the upper 100 m., that suggested 

 a correlation with the observed salinity dis- 

 tribution (fig. 21). The nodes of water of 

 relatively low salinity (California Current 

 Surface Water) correlate fairly well with 

 water of relatively high oxygen (depressed 

 isopleths), whereas the nodes of high salinity 

 (Gulf Surface Water) correlate with elevated 

 oxygen isopleths (diminished oxygen content). 

 It is not certain to what extent these correla- 

 tions are meaningful because, according to 

 the data, California water at the surface had 

 generally lower values of dissolved oxygenthan 

 the Gulf and Subtropical Pacific Surface Water. 

 The most likely cause of this lower oxygen 

 content was the upwelling of low-oxygen water 

 off western Lower California. At depths below 

 the thermocline, however, the oxygen content 

 of the California water generally exceeds that 

 of waters to the south and east- -as shown, 

 for example, by the reduced oxygen minimum 

 north of Cape San Lucas. 



In the Gulf entrance the water at the surface 

 is somewhat oversaturated. Thus along pro- 

 files 7 to 22 and line 153, the lower surface 

 oxygen values are to the west. In the profile 

 along line 23 to 37 and in the two profiles 

 farther to the south, the situation is reversed; 

 the oxygen content of water to the west, 

 identifiable from its salinity as having been 

 derived from California Current Surface 

 Water, has a higher oxygen content than the 

 Subtropical and Gulf waters to the east. It 

 seems as though the low-oxygen, upwelled 

 water from Lower California increased its 

 oxygen content as it spread southward at the 

 surface, perhaps by biological activity. 



29 



