toward a seasonal cycle associated with the 

 maximum heating of the surface layers. From 

 September to November 1967 the surface salin- 

 ity showed a gradual increase from about 35.10 

 to about 35.25 '>l„o. This second maximum was 

 observed in October. From November 1967 to 

 March 1968 there was a gradual decrease in 

 surface salinity to a low of about 34.70 o/oq. 



The salinity at the 100 and 200 meter levels 

 showed a considerable increase from December 

 1967 to January 1968 due to the convective 

 mixing mentioned above. Since the high tem- 

 perature at the surface creates a stable struc- 

 ture, it appears that the increase in salinity at 

 the surface promotes the convective process at 

 Ocean Station NOVEMBER. However, from 

 January to March 1968, there was a decrease 

 of salinity in the upper 200 meters. The salin- 

 ity below 400 meters showed little variability 

 during the observational period. 



VERTICAL PROPERTY DISTRIBUTION 



Envelopes of temperature and salinity ver- 

 sus depth have been constructed for each 

 cruise to Ocean Station NOVEMBER to show 

 the vertical structure in the water column and 

 to delineate the gross seasonal changes in 

 properties (figure 20-41). These envelopes re- 

 veal the basic thermohaline stratification of 

 properties at Ocean Station NOVEMBER: (1) 

 a surface mixed layer, varying from 10 to 150 

 meters in depth (2) the main thermocline from 

 200 to 600 meters in depth, and (3) the North 

 Pacific deep water below 600 meters. 



Ocean Station NOVEMBER is located in the 

 Subtropical Region of the Pacific Ocean which 

 is characterized by an excess of evaporation 

 over precipitation. The salinity of the water is 

 greatest at the surface and decreases to a mini- 

 mum between 200 and 800 meters in depth 

 (Tully, 1964). There is no permanent halocline 

 in this region and therefore the stability of the 

 density structure is solely dependent on the 

 temperature structure. The envelopes of tem- 

 perature versus depth (figures 20-30) illus- 

 trate the response of the surface waters to the 

 sea.sonal cycles of heating and cooling. From 

 March 1967 to May 1967 the eff'ects of winter 

 cooling were evidenced. The surface homoge- 

 neous layer (18.0-18.5° C. water) reached a 

 depth of about 100 meters in March and by 



May had increased in depth to nearly 150 me- 

 ters and the temperature was in the range of 

 17.9-18.9° C. with the exception of four anom- 

 alous stations where the temperatures dropped 

 to about 17.4° C. During the period from June 

 1967 to September 1967, the summer heating 

 established a seasonal thermocline in the upper 

 100 meters. In September when the maximum 

 surface temperatures of 24.5° C. were reached, 

 there was a negative gradient of almost 7.0° 

 C. in the upper 100 meters. In October 1967, 

 with the advent of a cooling season, the sur- 

 face temperatures decreased nearly 1.0°C and a 

 shallow mixed layer was formed of about 30 

 meters in depth. By December 1967 the surface 

 temperature had decreased to the range of 

 20.0-21.5° C. and the homogeneous layer had 

 increased in depth to about 50 meters. In Janu- 

 ary 1968 the mixed layer had reached a depth 

 of about 100 meters with temperatures in the 

 range of 19.0-20.5° C. From January to 

 March 1968 the temperature and extent of the 

 mixed layer changed very little, while the dom- 

 inant process appeared to be an increase of the 

 temperature in the depths between 100 and 400 

 meters. Little variability was observed in the 

 temperature of the water at the levels below 

 400 meters. From 600 meters to 1500 meters 

 the tem.perature showed a gradual decrease 

 from about 5.00° to 2.65°C. 



The dominant feature of the salinity versus 

 depth envelopes (figures 31-41) is the salinity 

 minimum located between 200 and 600 meters 

 in depth. The sampling program of sampling 

 at discrete levels obviously does not delineate 

 the continuous vertical structure, but several 

 major features are evident from the salinity 

 envelopes. There is a salinity minimum of 

 about 34.05-34.10 "/oo located at 200 meters. 

 This feature is present during most of the year 

 except during the late winter, January — Feb- 

 ruary, when the convective mixing increases 

 the salinity at this level to the range of 

 34.20-34.40 "/o,,. Associated with the salinity 

 minimum at 200 meters there is an interme- 

 diate maximum at 300 meters of about 

 34.10-34.15 %„,. 



A permanent feature of the vertical salinity 

 structure at Ocean Station NOVEMBER is the 

 minimum value between 400 and 600 meters. 



