The most pronounced difference between these 

 northern stations and those from farther west 

 is the presence of the salinity minimum at 100 

 to 230 meters (see fig. 62) instead of at the 

 surface. 



On 141°W. (fig. 71), the most 

 easterly transect, the curves had two common 

 features: all, except 79, formed a compact 

 band between 6.5 C. and 8. 5 C. , and all had 

 a deep and a shallow salinity minimum. As in 

 the deeper water of the western sections, sali- 

 nity gradually increased from north to south at 

 temperatures less than 6.5 C. Again the dif- 

 ference between the southernmost station, 

 station 79, and the adjoining station was suffi- 

 cient to indicate a distinct change in water 

 mass. 



At temperatures greater than 

 8.5 C. there were three abrupt shifts among 

 the curves. The most pronounced was between 

 stations 75 and 76, but there was such a large 

 space and time interval between these stations 

 because of heavy weather that the sharpness 

 and position of the break is suspect. South of 

 station 76 the curves lie just below the mini- 

 mum of Eastern North Pacific Central Water, 

 a slight decrease in salinity from the southern 

 stations of 147 W. North of station 75 the in- 

 flux of Subarctic Water is again apparent from 

 the large differences among the curves. All 

 of these, except between stations 72 and 73, 

 correspond to changes in the dynamic topogra- 

 phy along the transect. If the contours of the 

 dynamic topography at the surface are traced 

 to the west (upstream), the more northerly 

 origin of the surface water at station 72 is 

 obvious. 



Dissolved Oxygen 



The dissolved oxygen content of the 

 ocean provides an additional tool for tracing 

 the origin and movements of water masses. 

 It is absorbed at the sea surface in amounts 

 dependent upon the salinity and temperature of 

 the water and the pressure, which is usually 

 considered to be standard (1,013 mb. ), and 

 moisture content of the air, which is usually 

 neglected. Below the euphotic zone, biological 

 processes lead to the consumption of oxygen so 

 that the processes of diffusion and advection 

 must be such that, if the oxygen content of the 

 deeper layers remains constant, they lead to 

 a replenishment that exactly balances the con- 

 sumption (Seiwell 1937). 



The longitudinal profiles of 

 dissolved oxygen are shown in figures 72-81, 



the horizontal plot at 10 m. in figure 82, and the 

 distribution on the 26. 8 sigma-t surface in figure 

 83. The isopleths of percentage saturation have 

 been included on some of the plots to show the 

 degree of depletion of the subsurface oxygen and 

 hence the implied direction of movement, if the 

 consumption is assumed to be independent of the 

 oxygen content until it is nearly depleted (ZoBell 

 1940). The saturation values used to compute 

 the percentages were taken from Fox's tables 

 (Harvey 1928), which were computed on the as- 

 sumption that sometime during the past the water 

 had been at the surface in contact with dry air at 

 normal pressure (1013.3 mb. ) at the in situ 

 temperature and salinity. 



The 10-m. samples were used to 

 depict the dissolved oxygen content at the surface 

 because the surface Nansen bottle was frequently 

 in the turbulent area around the hull when the 

 vessel was rolling heavily. The distribution of 

 dissolved oxygen on the 10-m. surface (fig. 82) 

 followed the pattern indicated by the temperature 

 and salinity fields. The highest oxygen values 

 were at the northern edge of the area where the 

 lowest temperatures and salinities were observed, 

 and the least oxygen in the area just north of the 

 Hawaiian Islands, where the highest temperatures 

 and salinities were observed. 



The profiles of dissolved oxygen (figs. 

 72-81) show that the pattern of the vertical dis- 

 tribution is basically the same over the entire 

 area. It consists of a surface layer of almost 

 uniform content, a layer of small, variable nega- 

 tive gradient, a layer of large and almost uniform 

 negative gradient, and in a few of the sections a 

 layer in which the negative gradient decreases 

 and changes to a positive gradient. The latter 

 does not occur in all of the sections, since the 

 oxygen minimum was below 1, 000 m. in a large 

 number of cases (see observed data). 



As expected, at each station the 

 surface layer of almost uniform dissolved oxygen 

 content corresponded to the layer of uniform den- 

 sity resulting from wind and advective mixing. 

 In almost all cases the values in this layer were 

 within -0.05 ml. /I. of the 10-m. value. 



Instead of a rapid decrease in the 

 dissolved oxygen content just below the surface 

 layer, such as occurred in the temperature and 

 density fields, there was a layer of small and 

 variable negative gradient between the surface 

 and the band of large negative gradient. The 

 cross sections (figs. 72-81) show that the 

 4. 5-ml. /I. isopleth, which varies between 300- 

 550 m. in depth, approximates its lower limit. 

 It is deepest between 30 and 32 N. or at about 



10 



