694 EIGHTH PACIFIC SCIENCE CONGRESS 



the smiace layers. Since the mechanism of these changes is not im- 

 mediately clear, it will be a subject for further investigation. Off Green 

 Point, the whole water column was freshened as would be expected since 

 strong mixing occurs in that region and its water source is mainly the 

 surface layers of the main basin. Thus even under these extremel) 

 extended conditions of flood, a noticeable gradient can not be main- 

 tained beneath the surface layers and another mechanism must be 

 found to simulate the gradients which occur in nature. 



Since in nature the source water of the Strait of Juan de Fuca 

 does not hold a constant salinity throughout the year, the effects of a 

 change in source salinity was investigated in the model. In order to 

 make results clear-cut, a sudden decrease of salinity of 10°/oo was main- 

 tained for 166 days and then increased back to its original value. 



The decrease in source salinity (Fig. 9) was first noticed at Point 

 Jefferson. A uniform gradient to a depth of 100 meters developed 

 within 45 days. Subsequent mixing of these waters produced a homo- 

 geneous salinity to this depth with a sharp interface separating it from, 

 the more saline bottom water by 101 days. Mixing then gradually low- 

 ered the interface. The changes in salinity below 100 meters were 

 minor during the first 101 days. As would be expected from the proxi- 

 mity and lack of sill between Camano Head and Point Jefferson, the 

 sequence of events was very similar for the two stations. At Green Point, 

 the salinity decrease was later at the surface, but when it did occur 

 it was felt almost to the very bottom. After 166 days, the salinity was 

 homogeneous in the bottom layer. At Hood Point, the fresher water 

 was only noticed to a depth of 50 meters after 45 days, and only to 

 about 70 meters after 166 days with very little change in the salinity 

 of the bottom waters. Correspondingly, in nature the bottom water in 

 Hood Canal has a tendency to stagnate. 



An increase in source salinity produces a series of density gradients 

 markedly different than above in both shape and rate of change (Fig. 

 10). Within 24 days, there was a considerable increase in salinity of 

 the bottom water at Point Jefferson with the appearance of an almost 

 constant gradient between the depths of 30 and 150 meters. After 38 

 days, the surface gradient was increased to a depth of 50 meters and 

 decreased below that depth. This pattern continued until equilibrium 

 conditions were reached after 89 days. At Camano Head, the salinity 

 structure went through the same sequence although the mixing ap- 

 peared to be faster between 20 and 70 meters. At Green Point, the 

 increase in salinity was not great for the first 24 days, but thereafter 

 there Avas a marked increase of salinity at all levels but never with ap- 

 preciable grach'ents beloAv the surface layer. At Hood Point, the heavier 



