near-surface layer (fig. 6) . Stef Snsson and Richards 

 (1964, p. 374), on the other hand, have suggested 

 that offshore movement and subsequent sinking 

 (along isen tropic surfaces) of upwelled water which 

 has gained oxygen from photosynthesis would 

 "largely contribute to the formation of the (off- 

 shore vertical) maximum." If so, then the near- 

 surface horizontal maximum would presumably 

 result. It seems unlikely, however, that this 

 process alone could generate the vertical maximum 

 that occurs widely over the North Pacific; defini- 

 tive measurements — e.g., apparent phosphate up- 

 take (APU) in the layer of the offshore ox-ygen 

 maximum — are not yet available to indicate 

 whether the vertical oxygen maximum of the 

 plume and offshore provinces is derived from the 

 nearshore, near-surface horizontal maximum, or, 

 conversely, whether it produces the nearshore 

 maximum by upward displacement. 



Oxygen distribution in the near-surface layer 

 apparently was atypical in the summer of 1964 

 (fig. 6). The basic pattern described above was 

 altered in the plume by the presence of well- 

 developed pockets of high concentrations of oxy- 

 gen. Production of some pockets by phytoplankton 

 photosynthesis is indicated from their high degree 

 of supersaturation (106-110 percent) and from 

 generally large concentrations of chlorophyll a in 

 the plume and offshore province in 1964. High- 

 oxygen pockets were associated with low tem- 

 peratures (13-14.5° C. at 10 m.). Heterogeneity 

 of their mode of generation is indicated, however, 

 by the large corresponding range of salinity 

 (30.5-32°/oo at 10 m.), and one pocket, centered 

 at lat. 43.3° N. and long. 126.2° W., clearly was 

 produced as part of a dome formed by the motion 

 of a cyclonic eddy (fig. 11). 



Tonguelike patterns occur occasionally at greater 

 depths (100 m. or more) but not with sufficient 

 frequency to be considered recurrent or charac- 

 teristic. It is difficult to see how these tongues 

 could arise from the same mechanisms that pro- 

 duce near-surface tongues. Because of the nearly 

 uniform temperature-salinity relation beneath the 

 near-sm-face layer, the tongues at the greater 

 depths appear to be produced by the distribution 

 of mass associated with geostrophic flow. 



ANNUAL VARIATIONS 



Differences from year to year in extent and 

 character of provinces are generated by changes 



518 



in the dominant processes. The basic patterns 

 discussed in the previous section are not obscured, 

 however, but are altered only in degree. Effects 

 of these differences upon heating in the surface 

 layers are discernible. 



Extent and Character of Provinces 



The state of development of the nearshore 

 province is determined principally hy the inten- 

 sity' and duration of upwelling, w-hich in turn^ 

 depends upon, the nature of the coastal wind field 

 and upon local bnthymetrv. Because bathymetry 

 is fixed, betweeii-jear differences in the extent of 

 the nearshore province should be assignable to. 

 differences between years in the June and July 

 wind fields. A means of assessing the effect of 

 wind field on upwelling is provided by estimation 

 of average zonal components of Ekrnan transport 

 across the near-coast meridian 124.5° W. Wind 

 data for the study area in June and Jidy 1962-64 

 were obtained from monthly summaries of marine 

 weather observations for the Pacific Ocean pre- 

 pared b}' the Tuna Resources Laboratory, Bureau 

 of Commercial Fisheries, La Jolla, Calif., in the 

 form of average zonal and meridional components 

 of wind velocity by 1° squares. Average wind stress, 

 r (g. cm."' sec."*), was computed from average 

 wind velocity, U (assumed to have been measured 

 at 10 m. above sea surface), by the basic equation 



where air density, p, is taken to be constant at 

 1.2 X lO-'g. cm.-' and Co={l+0.07U) x 10"' (Deacon 

 and Webb, 1962, p. 61). The computing equation, 

 with constants adjusted for the use of Uin knots, is 



f=0.318f72(l -h0.036Z7) X 10-2 (1) 



Because instantaneous values of wind velocity 

 were not available from the sununary described 

 above, equation (1) was entered with averaged 

 values of wind speed (f/). Because {UY<^U-, 

 values of r used here miderestimate the true 

 averages of wind stress. 



Ekman transport, which is assumed not to 

 extend beyond the bottom of the pycnocline pro- 

 duced by the thermocline and plume halocline, 

 is given by integration of equations of motion with 

 appropriate boundary conditions; 



U.S. FISH AND WILDLIFE SBRVIOE 



