SOME CHARACTERISTICS OF SEA WATER STRUCTURE 



By John P. Tully 



Pacific Oceano graphic Group 

 Nanaimo, B.C., Canada 



Introduction 



Recent examination of nearly two thousand serial observations in 

 oceanic and coastal waters of the northeast Pacific Ocean has revealed 

 several general characteristics in the structure of the water in these 

 seas. Sea water occurs in zones of appreciable thickness with respect to 

 each property, and within each zone the measure of the property tends 

 to be a simple function of the logarithm of depth. 



These concepts of structure are illustrated in Figure 1 with simple 

 examples of salinity and temperature data. These have been plotted 

 in the usual way as natural functions of depth (natural-plot) and as 

 functions of the logarithm of depth (log-plot). These illustrate the 

 nature of the transformation. It is evident that there are two water 

 masses represented by the more homogeneous layers. These may be 

 designated as the upper and lower zones, which are separated by a tran- 

 sition or boimdary zone. It is also evident that within each zone the 

 values of the properties are linear functions of the logarithm of depth 

 (logarithmic giadients). 



Examination of Oceanographic Data 



The properties of the water may be observed at a series of depths 

 from the surface downwards (serial observation). From such data the 

 vertical structure is usually illustrated by plotting the values of the 

 properties as a function of depth and interpolating a smooth curve 

 through the points. This procedure is becoming more precise as instru- 

 ments, such as the bathythermograph, are being developed to make 

 continuous records while being lowered in the sea. The distribution 

 of properties in a locality is observed by making serial observations at 

 a number of positions in as short a time as possible (synoptic survey). 

 From these data plans and vertical sections are drawn, showing inter- 

 polated isometers of the sea water properties. 



In this analysis of the data from serial observations, the values of 

 the properties were plotted as functions of the depth on semi-logarith- 

 mic graph paper, and the points were joined by straight lines. In gen- 

 eral, small deviations were ignored and the best straight line was drawn 



643 



