ESTUARIXE MODEL OF SUB-ARCTIC PACIFIC OCEAN 443 



structure in the upper zone is destroyed by cooling and strong 

 winter winds. This overturn determines the upper limit D of the 

 halocline. 



Earlier studies (Hollister, 1956; Tully and Dodimead, 1957; 

 TuUy et al., 1959) have shown that there is a marked annual cycle 

 of heating and cooling in the upper zone. The amplitude decreases 

 with depth and becomes undetectable at about 120 m at Ocean 

 Weather Station "P." This depth exceeds the depth D of wind 

 mixing and includes the upper part of the halocline. In this zone, 

 the seasonal heat exchange cannot be due to the overturn phenom- 

 ena because of the presence of the salinity gradient in the halocline. 

 Hence it must be dependent on the downward transfer feature of 

 the entrainment process. 



Since water from the upper zone is mixed downwards in de- 

 creasing proportions to the lower limit L of the halocline, it is 

 evident that it must carry its temperature and all other properties 

 with it to this limit. However, the water being transferred down- 

 ward is being mixed with ever increasing proportions of water 

 originating at the limit L so that the surface-induced temperature 

 cycle is masked by variations in the entrained waters, and becomes 

 unrecognizable in the halocline. 



The variation of fresh water input with time is small. This is 

 evidenced by the studies of Doe (1955) and Dodimead (1958a) 

 which show that the surface salinity distribution (Figs. 3 and 4) 

 is consistent from winter to summer within about 0.2%o. There is 

 little or no seasonal variation of salinity at the limit D of the upper 

 zone. Hence the salinity gradient in the halocline is not a seasonal 

 function. 



It is concluded that the lower limit L of the halocline is well 

 below the limit of recognizable surface-induced seasonal variations 

 in the sub-Arctic Pacific Ocean. 



An Application of the Model 

 Identification of Halocline Water 



It has been established that all the sea water in the halocline 

 and upper zone of the sub-Arctic region enters these zones through 



