100 z 1961 



I 



1962 



100 z 1963 



1964 



Figure 9. — Vertical profiles of July density along lat. 44° 

 N. (approximately). Longitudinal relations between 

 profiles are preserved. Sea floor is stippled. Contour 

 interval is 0.2.5 a, unit except where shaded. Depth scale 

 is logarithmic. 



entrainment and diffusion produce lateral and 

 vertical flux of salt into the plume so that the 

 moving parcel loses its dilute character \nth time 

 and distance from its soiu-ce until it is indistin- 

 guishable from water of offshore origin. 



In the present treatment, the 32.2°/oo isohaline 

 is the criterion of the plume limit. This value was 

 chosen because 32.2°/oo conservatively specifies 

 the largest value of salinity in the salinity gradient 

 at the interface between the plume and surroinid- 

 ing water (figs. 4 and 8), beyond which the im- 

 mediate physical influence of the plume is much 

 diminished. The plume province thus may be 

 defined as the portion of the area over which sur- 



face salinity is less than 32.2%o. Geographic 

 limits of the plume, as defined by Budinger et al. 

 (1964) for examining the fresh- water budget, were 

 given by the location of the 32.5°/oo isohaline. 

 By this criterion, plume in summer has been de- 

 tectable south of lat. 42° N. and as far as 300 

 nautical miles (560 km.) offshore (fig. 4), although 

 the plume province itself does not extend so far. 

 The secondary halocline between plume and 

 underlying water partly coincides \\-ith the summer 

 thermocline (compare figs. 7 and 8 above 50 m. 

 depth). This superposition notably increases the 

 vertical density gradient dp/ds over the extent 

 of the pliune province. Stabihty, related to the 



density gradient approximately by ^ is also 



high; in July 1964, for example, average plume 

 stability at 14.2 x 10"^ cm."' was about 80 percent 

 greater than average stability in the corresponding 

 pycnocline beyond the plume. 



Of shore Province. — The third subdivision, which 

 lies seaward of the plume province, is termed the 

 offshore province. Its character is identical with 

 the eastern extreme of the subarctic region 

 termed "Transitional Domam" by Dodunead 

 et al. (1963), in that it is subarctic water with 

 temperatures in excess of 7° C. at the top of the 

 halocline. The offshore province may also be con- 

 sidered to be part of the upstream source of the 

 California Ciurent, since at least some of the 

 water flows southward off the coast of California. 

 The offshore province exhibits the vertical salinity 

 and temperature structure characteristic of the 

 eastern subarctic as a whole (fig. 2)— a deep, per- 

 manent halocline through which temperatures are 

 nearly constant, and a separate, overlying summer 

 thermocline. No strong secondary halocline is pres- 

 ent, and salinity increases gradually and con- 

 tinuously mth increasing depth through the layer 

 between the summer thermocline and permanent 

 halocline (fig. 8). 

 Lower Zone 



Below the main halocline, coastal runoff has no 

 direct physical influence so that only two prov- 

 inces, nearshore and offshore, are distinguishable. 



The nearshore lower zone is deflned here as the 

 region where the field of motion and bottom topog- 

 raphy produce significant onshore ascent ^ of 



- Ascent is here considered significant If the slope of isopletlis monotonically 

 exceeds 10-' over more tlian two sampling locations. The term "monotonic" 

 refers in this paper to slopes with no maxima or minima, i.e., <>-ldz^ = 0. 



OCEANOGRAPHIO CONDITIONS IN NORTHEAST PAOIFIG OCEAN 



611 



