PHYSICAL OCEANOGBAPHY OF THE GULF OF MAINE 



925 



The vertical stability varies little from season to season in the bottom stratum 

 deeper than 100 meters, indicating comparative uniformity in the activity of vertical 

 circulation there; but wide seasonal fluctuations in the stabiUty of the superficial 

 stratum reflect corresponding differences in the stirring effects of the tides, etc. 



.s 



w 



Fig. 185.— Difference in density between the surface and the 40-meter level for May, 1915 and 1920. Corrected 



for compression 



In northern coastal waters generally (the Gulf of Maine is no exception) vertical 

 mixing of the upper 100 meters is most active during the coldest season, when, thanks 

 to low surface temperature, the water has little stability; and it is at this season 

 37755—27 27 



