20 (&z) feet. (Several depth intervals were tried but 20 feet 

 yielded the greatest detail for the minimum interval.) This dis- 

 placement of one smoothed temperature chart over the other 

 caused isotherms of one to intersect isotherms of the other. 

 Next, at points of isotherm intersection the temperature values 

 of one chart were subtracted from the values of the other. This 

 yielded the change in temperature (\T) at particular depths and 

 times for &z . Finally, the resulting vertical-temperature- 

 gradient field of computed values of AT A.? was contoured at 

 selected gradient-strength intervals. 



Figure 5 shows the contoured vertical-temperature- 

 gradient field obtained by this differentiation process from the 

 smoothed structure of Sample Area 8 (fig. 4). The vertical and 

 horizontal scales for the gradient field correspond in both depth 

 and time to the smoothed structure from which it was derived. 

 The contoured values in figure 5 have been multiplied by 100 for 

 convenience of presentation. The vertical-temperature-gradient 

 field is all negative, because temperature decreases with respect 

 to depth for the entire field. The vertical-temperature-gradient 

 fields for the other 16 sample areas are contained in Appendix B. 



The same method of differentiation was used to obtain the 

 horizontal-gradient field. Here the horizontal differential incre- 

 ment, Ax, was 1000 feet. (Several values were tried, but 1000 

 feet provided the greatest detail for the smallest interval.) This 

 provided the change in temperature (AT) for the horizontal distance 

 increment (Ax). The resulting horizontal-temperature-gradient 

 field of computed values of AT Ax was contoured at selected 

 gradient-strength intervals . The contoured horizontal- 

 temperature-gradient field obtained by differentiation from the 

 smoothed structure of Sample Area 8 is shown in figure 6. The 

 vertical and horizontal scales for the gradient field correspond in 

 both depth and time to the smoothed structure from which it was 

 derived. The contoured gradient strengths in figure 6 have been 

 multiplied by 10 ' 4 for convenience of presentation. The actual 

 values of the gradient strengths are in degrees Celsius per foot 

 times 10~ . 



Assuming wave motion, the zero-horizontal-gradient con- 

 tours that are vertical denote phase multiples of A- 2 (for N odd) 

 in a lateral direction. The zero contours that are horizontal de- 

 note the location of nodes in the modal distribution in the vertical 



16 



