Figure 12.- — Wind-driven (Ekman) transport vectors 

 by 1° increments of latitude, averaged between longs. 

 124° W. and 130° W. Length of vectors gives transport 

 in g. cm."' sec."' according to the scale below figure. 



influences heat constraint, and therefore tempera- 

 ture distribution, is provided by figure 14. As 

 imphed by figure 2, the permanent halocHne is 

 the lower Hmit of winter mixing; consequently 

 temperature near the top of the permanent 

 halocline is nearly identical to that of the mi.xed 

 layer in the previous winter (Dodimead et al., 

 1963). Hence the July difference between tempera- 

 ture at the sea surface and the temperature where 

 salinity equals 33°/oo, located within the halocline, 

 is a measure of mixed-layer temperature change, 

 AG, from the previous winter. The area of greater 

 temperature change substantially corresponds to 

 the plume province as defined by surface salinity 

 distributions (fig. 4). 



The summer tongue of lower density in the 

 plume province (flg. 5) is produced by the coin- 

 cidence of tongues of low salinity and high tem- 

 perature described above. 



Distribution of oxygen concentration in the 

 near-surface layers is more complicated than that 

 of the preceding variables. Shoreward of the 

 minimum (5.4-6.5 ml./l.) in the plume province 

 are a maximum (6.6-8.0 ml./l.) in the seaward 

 portion of the nearshore province and a minimum 

 (2.0-5.0 ml./l.) nearest the coast. These extremes 

 combine to produce the trough-and-ridge oxygen 

 distribution that was characteristic of the area 

 in each summer in 1961-64, except the last 

 (fig. 6). 



The oxygen mininium in the plume is the 

 result of the larger infiuence of reduced oxygen 

 solubility at higher temperatures over the opposite 

 influence of higher oxygen solubility at reduced 

 salinities. Since the degree to which waters of the 



surface layer are saturated with oxygen is the 

 same in the offshore as in the plume province 

 (about 104 percent), this variation is not at- 

 tributable to differences in biological processes. 



In the horizontal distribution of oxygen, the 

 presence of both the minimum and maximum 

 concentrations in the surface layer of the nearshore 

 province is the product of one or both of two 

 effects of upwelling. Upwelling transports nutrient- 

 rich water that is undersaturated with oxygen 

 into the photic zone, where algal photosynthesis 

 increases the oxygen concentration sufficiently to 

 produce supersaturation. If the transfer of oxygen 

 from the air to the sea proceeds faster than the 

 transfer of heat, supersatm-ation can result 

 independently from this purely physical process. 

 The oxygen minimum along the coastal portion 

 of the nearshore province may thus represent 

 that part of the upwelling system where the 

 residence time of low-oxygen water in the surface 

 layer has been too short to exhibit effects of local 

 o.xygen gain by photosynthesis and atmospheric 

 exchange. Conversely, the maximum in the outer 

 part of the nearshore province represents the area 

 where one or both processes have been operating 

 for sufficient time to effect supersaturation. Large 

 standing stocks of phytoplankton, indicated by 

 higher chlorophyll concentrations (Owen, 1967b) 

 and larger rates of carbon assimilation nearshore 

 (AndersoJi, 1963), support the hypothesis of 

 greater oxygen production by photosynthesis in 

 the fertile nearshore province than beyond. That 

 local processes of oxygen gain are effective in this 

 province is evident from the decreased slopes of 

 near-surface oxygen isopleths (flg. 10) relative to 

 isohaline slopes (fig. 8). In the absence of local 

 oxygen gain, these slopes would be identical. 



The nearshore maximum in the horizontal dis- 

 tribution of oxygen may also be ascribed to a 

 more direct effect of upwelling. Seaward of the 

 nearshore province, a maximum value (5-7 ml./l.) 

 in the vertical distribution of oxygen concentra- 

 tion occurs in summer at depths of 30 to 70 m. 

 (fig. 10). This maximum is not confined to the 

 present area, but is present over large parts of the 

 North Pacific, where it has been ascribed to sum- 

 mer loss of oxygen above the layer in which the 

 maximum occurs (Reid, 1962; Pytkowicz, 1964). 

 Simimer upwelling in the nearshore province 

 would displace the layer of this oxygen maximum 

 upward to form the horizontal maximum in the 



OOEANOGRAPHIC CONDITIONS IN NORTHEAST PACIFIC OCEAN 



515 



