VARIABILITY 



Changes in sea temperature at the surface and at various 

 depths, which thus change the depth of isotherms, may be attrib- 

 uted 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; internal waves; and others.®' 

 Since all the factors simultaneously exert influence, it is difficult 

 to determine their individual effects . 



Several investigators have made studies of the variability of 

 surface and subsurface sea temperatures. " Others have devel- 

 oped methods for the statistical analysis of physical properties ap- 

 plicable to sea temperature variability.^ "^ In this report, 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 first method of presenting the isotherm variability is by 

 depth differences from point to point along the isotherm. For this 

 the depths of isotherms were scaled from the original record in 

 each section at half-minute intervals. 



The selected sections are listed in table 1 . One of the iso- 

 therms chosen for analysis was located in the main thermocline 

 and the other below the main thermocline. These must also be at 

 a level where the sensors were operating properly. Those chosen 

 in the data section (fig. 3) were the 18° and 23 °C isotherms. 



The depth differences from point to point along the isotherms 

 were determined from the formula: 



10 



