continues east along the northern side of the 

 Eastern Gyre. However, as has already been 

 pointed out in the discussion of the temperature - 

 salinity relationships, a series of abrupt shifts 

 occur in the surface portion of the T-S curves, 

 showing an intrusion of colder and less saline 

 water from the north. A complete transition 

 to Subarctic Water was not made on any of the 

 transects, so the core of the Aleutian Current, 

 being defined as an easterly flow of Subarctic 

 Water, was not reached. 



Previous authors have shown 

 considerable variation in the latitude, extent, 

 and nature of the eastern portion of the transi- 

 tion zone between the North Pacific Current 

 and the Aleutian Current. Merz's chart of the 

 currents of the Pacific in northern summer 

 (Wiist 1929) shows it as a line beginning off the 

 coast of Japan at about 36 N. and extending in 

 a wide arc through 42 N. , 170 E., to about 

 35 N. latitude, 160 W. longitude. He applies 

 the name North Polar Front to the line. Schott 

 (Deutsche Seewarte 1942) shows the transition 

 as a line of convergence which corresponds to 

 Merz's from the coast of Japan to 170 E., 

 42 N. It then continues northeast as an indefi- 

 nite line to 45 N. latitude, 165 W. longitude. 

 In the area north of the Hawaiian Islands, Schott 

 indicates the line of divergence shown in figure 

 17. Sverdrup et al. (1942, figs. 205 and 209A) 

 show the transition zone as the boundary be- 

 tween the Subarctic Water and the Eastern and 

 Western North Pacific Central Water masses. 

 They portray it as a zone extending in a wide 

 arc completely across the Pacific. It also 

 corresponds to Merz's Polar Front to about 

 180 . It then continues to about40°N., 150°W., 

 where it turns southward and parallels the 

 coast of North America to approximately 20 N. 



The differences in interpretation 

 by the three authors are quite understandable 

 when the small amount of data and the different 

 methods used in the analysis of the circulation 

 are considered. Schott used ship's drift, 

 Sverdrup largely temperature-salinity rela- 

 tionships andMerz apparently a combination 

 of both. However, Merz did not have the 

 benefit of more recent surveys such as those 

 of the Carnegie and the Bushnell. Actually, 

 the major differences among these authors' 

 interpretations of the cruise area can be rec- 

 onciled. In the area where Schott shows a 

 divergence in the surface current, Sverdrup 

 et al. (1942, fig. 205) indicate a branching or 

 divergence of the North Pacific Current. Wiist, 

 in his discussion of Merz's North Polar Front, 

 states that in the eastern part of the ocean, 

 although the front has the unstable temperature 



characteristics of a convergence in the direction 

 of flow, it shows mixing of the colder, deeper 

 waters with the surface water. This would cause 

 enrichment and cooling of the surface, which are 

 the two most outstanding characteristics of an 

 area of divergence. 



If it is remembered that in the ocean 

 an abrupt, discontinuous transition from one type 

 of water to another is almost never found and 

 that the line merely indicates that the transition 

 takes place over a relatively short distance, 

 Wiist's geographical limits of and description of 

 the eastern part of the North Polar Front seem 

 to fit the northwestern part of the cruise area. 

 The T-S curves show that the incursion of the 

 Subarctic Water took place in the form of a 

 series of narrow streams rather than a broadly 

 moving front. The dynamic topography shows 

 that the bands of relatively high velocity, which 

 resemble the multiple currents of the Gulf 

 Stream described by Fuglister (1951), occurred 

 in the boundaries between these streams. The 

 turbulence in these zones of relatively large 

 horizontal velocity gradient probably cause the 

 mixing of the deep water with the surface waters 

 described by Wiist and accounts for the large 

 horizontal phosphate gradients in these zones 

 and the occurrence of the highest phosphate 

 values in the northwest part of the area. 



The reported existence of the North 

 Pacific Gyral, a clockwise gyral centered between 

 the Hawaiian Islands and the west coast of North 

 America, is based mainly on the characteristics 

 of the water and results of current and mass 

 transport computations (Sverdrup et al. 1942, p. 

 723). Its center is believed to coincide with the 

 center of the Eastern North Pacific High, so it 

 undergoes considerable seasonal migration and 

 variation in size. Considering the radical shift 

 that occurred in the mean position of the High be- 

 btween February and March, it is not surprising 

 that there was little evidence of a distinct gyral 

 in the dynamic topography of the eastern part of 

 the area. However, many of the other character- 

 istics of the Gyral were present in the southeast- 

 ern part of the cruise area. The isolated cell of 

 sigma-t greater than 25.0 at the surface, the 

 topography of the shallow salinity minimum, and 



the close approximation of the T-S curves at the 



o o 



southern stations on the 147 W. and 141 W. lon- 

 gitude transects to those of the Eastern North 

 Pacific Central Water show that it is centered at 

 about the southernmost of the two anticyclonic 

 cells on 145 W. longitude. The maximum depths 

 of up to 200 m. of the top of the thermocline which 

 occurred just south of the center of this cell il- 

 lustrate the effect of convergence in the surface 

 waters. The impoverishment of the southern 



14 



