The detailed recording of isotherm depths indicates the 

 complicated character of the thermal structure of the seas. It 

 also emphasizes that the ocean is probably a complex body, not 

 only as regards temperature, but also as regards chemical, bio- 

 logical, and other aspects. 



ISOTHERM DEPTH VARIABILITY 



Changes in sea temperature at the surface and at various 

 depths may be attributed to any of several factors, among which 

 are the advection of water of different temperature into an area, 

 radiation from the sun, mixing by the wind, tidal currents, inter- 

 nal waves, and others. 7 Since all the factors simultaneously 

 exert influence, it is difficult to sort out their individual effects. 

 It is equally difficult to adequately describe the structure and vari- 

 ability of the sea temperature. 



Several investigators have made studies of the variability of 

 surface and internal temperatures. ' ' ' Others have devel- 



oped methods for the statistical analysis of physical properties 

 applicable to sea temperature variability. 18 ' 13>14 ' 15 > :1S in this re- 

 port three approaches to the study of isotherm depth variability 

 are used: (1) differences in depth values; (2) autocorrelation of 

 depth values; and (3) power spectrum of depth values. 



Differences in Depth Values 



The depths of isotherms were scaled from the original rec- 

 ord (figs. 3 - 7) at half-minute intervals. The isotherms chosen 

 were 9°C for all legs, 14°C for the alongshore leg, and 16 °C for 

 the onshore leg. The depth differences from point to point along 

 the isotherms were determined from the formula 



x i ~ X i+1 = Y k 



18 



