55 



by internal waves, although the changes may also have been 

 caused by the irregular shifting of the various units in 

 response to short period fluctuations in the current system. 



Generally, the Subsurface Unit ranged in temperature 

 from 48° to 53°, and the Surface Unit from 56° to 68°F, 

 including the intermediate subunit with the two surface units 

 discussed in the preceding section. 



July 1956 



For comparative purposes, the water unit structure for 

 July 1956 is shown in Figure 17. 



Marked differences are seen in the patterns when compared 

 with the temperatures of the same month in the previous year. 

 While a warm surface unit lying above a cooler subsurface 

 unit was present in both years, the major differences existed 

 in the subsurface layer temperatures. Where the subsurface 

 water in July 1955 ranged from 48° to 53° over the shelf, in 

 July 1956, the range was from 53° to 56°F. The Surface Unit 

 is comparable to that of the previous year with a range, 

 including the intermediate subunit, of 58° to 70°F. However, 

 the Surface Unit was much thicker in 1956, reaching average 

 depths of 70 to 80 feet. 



Bottom water temperatures (Table II) were normally quite 

 uniform, but changes did occur in a non-seasonal manner. An 

 examination of bathythermograms also shows that in water 

 deeper than 100 feet, the temperature remained essentially 

 stable over periods of several days. A 53°F subunit was 

 present in all seasons, and if this water represents the 

 normal for the basic shelf water unit, then it is apparent 



