664 EIGHTH PACIFIC SCIENCE CONGRESS 



i.e. the prevalence of the intermediate water, was associated with the 

 anomalous Kuroshio conditions in recent years (1935-47). 



The northern intermediate water appears to extend conspicuously 

 to south along the Japan Trench and invades in the sea basin south 

 to Japan. Going south further, it descends to its deepest layer beneath 

 the depth of 800 m. in the sea-region at about 34-24 °N. with the sal- 

 inity of 34.0-34.2 Voo and rises again gradually up to the depth of 200 m. 

 at about 5°N., showing the increase of salinity to 34.5 Voo- 



The northern and southern intermediate waters collide with e-icJi 

 other in the zonal region of the latitudes of 12°-2°N., lying at about 

 the depth of 200 m. for the former (the Northern Intermediate Water) 

 and at about the depth of 800 m. (600-1000 m. depth) for the latter 

 (the Southern Intermediate Water). 



Accordingly in that region the vertical distrilTution of salinity shows 

 the double minimum which is produced by the stratification of the 

 southern intermediate water beneath the northern intermediate water. 



The distribution of the depth and the value of the maximum 

 salinity Smax.' ^^ the subsurface tropical water mass (Fig. 5) in- 

 dicates obviously in the deepest layer (100-200 m. depth). Sj„ax. ^^^ 

 in the regions of the North Equatorial Current (latitudes 20°-10°N.) 

 and in the Kuroshio area. It lies in the shallowest layer (0-100 m. 

 depth) in the western part of the North Pacific Saline Water (Salinity 

 more than 35 °/oo)» having its axis along the line of Subtropical Converg- 

 ence (water temperature in the upper layer above the 100 m. depth in- 

 creases suddenly in the south over this Convergence). 



In the Equatorial Counter Current area the depth of S.^ax. again 

 rises to its shallowest (depth almost less than 100 m.) above the opti- 

 mum angling depth of tuna with the salinity of about 34.8 °/oo or less, 

 which corresponds to the belt pf the cold water (water temperature 

 less than those in the surrounding north and south). 



Beyond it to the south (latitudes 3°N.-3°S.), again the S^^x. layer 

 sinks beneath 100-200 m. depth with the high salinity of 35.0-35.7 °/oo, 

 which corresponds to the water of the South Equatorial Current. 



The distribution of surface salinity in winter and summer during 

 the period 1931-35 (Fig, 6) shows the expansion of the North Pacific 

 Central Saline Water mass in winter, lying in the zone of lat. 20°-30°N. 

 around the axis of 22 °-26°N., 165°-180°E., and the shrinkage in sum- 

 mer season in the period of 1931-35. 



The water mass of low surface salinity (34.0-34.3 Voo) lying in the 

 zone of the Equatorial Counter Current (lat. 5°-12°N.) which cor- 

 responds to the Equatorial Calm or Equatorial Rainy zone, and also 



