in order to depict the salient features of the 

 latitudinal and longitudinal changes. The limit- 

 ing T-S curves of the three water masses into 

 which the waters of the North Pacific are 

 commonly divided (Sverdrup et al. 1942) are 

 included in each plot for comparative purposes. 



In the western part of the area 

 (160 W.), the curves lie along the lower sali- 

 nity limit of the Western North Pacific Central 

 Water (fig. 68), except in the upper 100-200 m. 

 and at temperatures of less than 8 C. at sta- 

 tions 3 and 28. At 8 C. , the temperature at 

 which the curves delineating the lower salinity 

 limits of the Eastern Central Pacific Water 

 and the Western North Pacific Water intersect, 

 stations 3 and 28 depart abruptly from the 

 other curves and follow the Eastern North 

 Pacific Central Water. 



At the shallower depths along 

 160 W. the interval between stations 22 and 23 

 (fig. 68) is the transition zone between the 

 southern stations which have a salinity maxi- 

 mum at or near the surface and the northern 

 stations which have a minimum at or near the 

 surface. The shallow maximum at the southern 

 stations is characteristic of a region where 

 evaporation produces an increase in salinity at 

 the surface, causing the water to sink and 

 spread out at an intermediate depth. Instead 

 of showing a gradual shift toward lower tem- 

 peratures and salinities, the surface portion 

 of the curves for the northern stations show an 

 uneven change in temperature-salinity relation- 

 ships. The small changes (e.g., sta. 17-18) 

 correspond to and account for the relatively 

 level zones in the dynamic heights. The large 

 changes (e. g. , sta. 18- 19) represent transitions 

 between waters of slightly different type and 

 correspond to zones of relatively large geo- 

 strophic currents. The irregular shift between 

 the curves leads to the conclusion that the 

 decreased temperature and salinity in the 

 surface layers are the result of masses of 

 water of more northerly origin, that is, water 

 containing greater percentages of Subarctic 

 Water, being driven into the area by the winter 

 westerlies instead of being simply the result of 

 latitudinal changes of temperature and rate of 

 precipitation or evaporation. 



Moving east to 155°W. (fig. 69), 



the curves form a less compact band but still 



lie just below the lower salinity limit of the 



Western North Pacific Central Water, except 



o 

 at temperatures of less than 7 C. , and in the 



surface water (upper 100-200 m. ). At tem- 

 peratures of less than 7 C. the curves do not 

 follow the standard curves as closely as they 



did on 160 W. The discontinuity between the twoi 

 southern stations (31 and 32) and the remainder 

 of the stations is not as pronounced as on 160 W. , 

 the maximum difference amounting to only 

 0. 1 /oo. In the surface waters the abrupt change 

 in the shape and position of the curves indicating 

 the transition from the southern stations having 

 a salinity maximum at or near the surface and 

 the northern stations with a minimum at the sur- 

 face occurs between stations 37 and 38. Again 

 the sharp changes between the two groups of 

 stations and within the groups correspond t o 

 zones of relatively large geostrophic current 

 velocities. 



The 147°W. transect (fig. 70) 

 intersects the complex eddy system in the north- 

 east part of the area, so the changes in the 

 temperature -salinity relationships reflect the 

 complex circulation around the eddies as well as 

 the expected changes with latitude. Except for 



station 58, the curves along 147 W. form a com- 



o „o 



pact band between 7 and 10 C. just below the 



lower salinity limits of the Western North Pacific 

 Central Water. For the most part below 7 C. the 

 salinity shows a gradual decrease at a given 

 temperature from south to north with occasional 

 slight reversals. As can be seen from the plot, 

 the difference between the curve for station 82, 

 the southernmost station, and those of the adjoin- 

 ing stations was the only one consistent enough to 

 indicate a change in water mass. 



At temperatures greater than 10 C. 

 along 147 W. there is a sharp shift in temperature- 

 salinity relationships between southern and 

 northern stations, the change occurring between 

 stations 55 and 56. Considering the southern 

 stations, the only significant change is a shift be- 

 tween 17 C. and 10 C. from the lower salinity 

 limit of the Eastern North Pacific Central Water 

 to just below the lower limit of the Western North 

 Pacific Central Water. The reason for the shift 

 and the correspondence of the curves to Eastern 

 North Pacific Central Water above 10 C. is ap- 

 parent from the slight secondary salinity minimum 

 which occurs at about 14 C. at stations 84, 85, 

 and 55. This indicates that there is a subsurface 

 influx of less saline water centered at about the 

 25. 6 sigma-t surface. The extent and possible 

 origin of the minimum is discussed in the section 

 on salinity. 



Because of the confused circulation 



resulting from the eddies there are no systematic 



shifts among the surface portions of the T-S 



o 

 curves at the northern stations on 147 W. For 



example, the salinities at all temperatures at 



station 58 were less than those at 59 and less 



than those at 60 at temperatures below 1 1 C. 



