observations (table 1) were obtained because 

 even in good weather the rolling motion of the 

 vessel frequently generated an opaque layer of 

 foam around the vessel. 



DISCUSSION 



Many of the similarities and 

 differences between the circulation pattern and 

 the distribution of the various chemical and 

 physical fields observed on this cruise and 

 those described by previous writers have been 

 discussed in the description of these fields. 

 Most of the differences can be attributed to the 

 fact that many of the previous discussions have 

 been either based on data taken during summer 

 months, e.g., Carnegie data (Sverdrup et al. 

 1945), or have been based on averages from 

 data taken over a number of years, e. g. , 

 (Schott's current chart)(Deutsche Seewarte 1942^ 



The most comprehensive summary 

 of the general features of the physical oceano- 

 graphy of the cruise area was given by Sverdrup 

 in his discussion of the water masses and cur- 

 rents of the oceans (Sverdrup et al. 1942, 

 Sverdrup 1943). According to his charts of the 

 water masses and mass transport of the North 

 Pacific (Sverdrup et al. 1942, figures 196 and 

 205, and chart VII), the cruise covered one of 

 the most complex areas of the North Pacific, 

 including the broad transition zone between the 

 Western and Eastern North Pacific Central 

 Water masses and the transition zone between 

 these water masses and the Subarctic Water. 

 Under average conditions the cruise area 

 should have included parts of the following 

 major components of the North Pacific circu- 

 lation: the North Equatorial Current, the 

 North Pacific Current, the Subtropical Con- 

 vergence, the Arctic Convergence or the North 

 Polar Front, and the Eastern Gyral or Gyre. 



The North Equatorial Current is 

 the name given to the westerly flowing current 

 in the lower north latitudes of the central 

 Pacific. The geostrophic currents indicated by 

 the dynamic topography (fig. 17-21) show only 

 a small area of westerly flow just north of the 

 Hawaiian Islands, the northerly limit of which 

 shifts slightly to the north with depth. Within 

 the westerly flow, except for the small cell of 

 >0. 2 (xg. at. /I. of inorganic phosphate at the 

 surface at station 3 (fig. 23), there is no evi- 

 dence of mixing, other than normal diffusion, 

 of sufficient magnitude to cause enrichment of 

 the euphotic zone (upper 80-100 m. ). Station 

 3 is just north of Kauai, and the slightly higher 

 phosphate content of the surface here was 



probably the result of the turbulence induced by 

 the flow around the islands. 



The Subtropical Convergence has 

 already been defined (page 4) as the zone of 

 convergence between the easterly flowing water 

 to the north, the North Pacific Current, and the 

 westerly flowing water to the south, the North 

 Equatorial Current. The position, northerly 

 shift, and broadening of the transition zone with 

 depth have already been pointed out. The rela- 

 tively large horizontal sigma-t gradients at the 

 surface (fig. 37) illustrate the rapid poleward 

 increase in density of the upper layers which is 

 associated with the Subtropical Convergence 

 (Sverdrup et al. 1942, p. 140). The occurrence 

 of the salinity maximum at the surface in the 

 area (figs. 51 and 52-61) indicates that it is part 

 of the source of the subsurface salinity maximum 

 found in the lower latitudes of the central North 

 Pacific. Thus, it is an area of subsidence and 

 should be unproductive. This is borne out by the 

 low phosphate content of the surface waters (figs. 

 84 and 85-93). 



The North Pacific Current is the 

 name applied to the general eastward flow of 

 warm water to the east of 160 E. It s e n d s 

 branches to the south, and normally the greater 

 part has turned south before reaching 150 W. so 

 that only a small portion flows south to the east 

 of the Hawaiian Islands. The similarity of the 

 T-S curves from the western part of the area to 

 those of the western North Pacific Central Water 

 (figs. 68-71) is evidence that the band of south- 

 easterly flowing water whose northeastern limit 

 is approximated by the 1. 72-dynamic-meter con- 

 tour at the surface (fig. 17) is a southern branch 

 of this North Pacific Current which has penetra- 

 ted farther east than normal. This was probably 

 the result of the southeasterly shift of the limits 

 of the westerlies and trades, which the January 

 and February 1954 mean sea level pressure 

 charts indicate was even farther than usual. The 

 only evidence of enrichment of the surface layers 

 within the North Pacific Current was at station 8 

 at 30 N. on 165 W. , where the surface phosphate 

 values were between 0.4-0.5 (ig. at. /I. Although 

 this station was located in an area of relatively 

 large and divergent surface currents, the local 

 nature of the high phosphate content and the fact 

 that the station was occupied just after a period 

 of Beaufort 7 winds lead to the conclusion that it 

 was a local phenomenon. 



When the geostrophic currents are 

 considered alone, the general easterly flow in the 

 northern part of the cruise area appears to be a 

 branch of the North Pacific Current, which 



13 



