- 30 - 



due to the lack of fresh wnter run-off from the Ifind. Freshet 

 effects nre ogoin evidenced In early Mpy. 



III. Discussion 

 It nmy be seen thnt the vqrintions in tempernture nnd salinity, 

 BS reflected ^t St=»tion 3, are indicative of vertical mixinir of the 

 wnters of the various levels. This mixing is brought ?ibout by the 

 following two ngencieg : 



is) Tldnl mixing -and upwelling which F>re common throughout the Bqy, 

 (b) Mixing resulting from seasonal changes in density. 



The density of the water is determined by its temperature 

 and salinity, the minimum density occurring during the summer ^nd 

 the maximum in the winter time. As the densities fluctuate between 

 these maxima and minima, there are times when the surface waters, which 

 have the greater range, have the same density as the subsurface waters o 

 This greatly facilitates vertical mixing through tid^l and wind action 

 so that in time a thick isopynic layer is developed, at times reaching 

 nearly to the bottom. This mixing causes an interchange between the 

 waters at various levels. In 1916, this interchange was completed by 

 the latter part of March. The interche-nge may not hs^ve occurred from 

 top to bottom throughout, but it did take place in certain l^^yers, at 

 least throughout a period extending from early November to late M^rch, 

 The Intensive interchange must have token place In l^te November and 

 was slowed considerably by a freshening of the surface waters and an 

 increase in the salinity of the bottom v/aters. From early April 

 onwards the heating and freshening of the surface layers bring about 

 stable conditions that ^re not overcome until late November when 

 interchange between the surface water ^nd the water at the 50 metre 



