OCEANOGRAPHIC INFORMATION FOR SUBMARINE CABLES 1077 



One method of understanding temperature changes is to consider the 

 movement of the water masses. These movements depend on density 

 gradients which are directly dependent on the sahnity and temperature. 

 This type of study is apphcable in shallow water where circulation of the 

 surface layers is brisk. For the deep sea, however, dynamic calculations 

 are ambiguous; different investigators ushig the same data not only 

 arrive at different values for velocity but often arrive at opposite direc- 

 tions of flow. Thus, continuity considerations and the conservation of 

 volume are the primary factors in studies of the deep-water circulation. 

 It is important when evaluating temperature data and studying tem- 

 perature change and rate of bottom water circulation to study the entire 

 process and not be limited to temperature observations, even though 

 the temperature is the desired final answer. 



4.3 Temperature in the North Atlantic 



4.3.1 General 



Ocean-bottom temperatures in shallow water (less than 200 meters 

 deep) are affected by seasonal air temperatures and movements of local 

 masses of water. Thus, each specific area exhibits its own pattern of 

 temperature changes. Data are fairly abundant in shallow water areas, 

 so that despite the large and often erratic changes, it is generally pos- 

 sible to determine roughly the bottom-temperature cycle from existing 

 data. However, the local nature of the phenomena makes it desirable to 

 concentrate any detailed studies on areas of immediate interest rather 

 than to attempt broad generalizations. 



In deep water (depth greater than 200 meters) bottom temperatures 

 and their variations result from large-scale, oceanwide topographical and 

 \ circulation phenomena. At the same time, the paucity of data makes 

 an analysis of any particular locale quite difficult. Thus, a general study 

 of deep-water bottom temperatures in the North Atlantic presents the 

 best hope of obtaining at least some useful data. 



4.3.2 Shallow Water (Depth less than 200 Meters) 



In many shallow-water areas near shore (depth less than 50 meters) 

 there are predictable seasonal chang(\s in temperatuio of the order of 

 10°C. In harbors and bays where interchange with open ocean water is 

 restricted the seasonal temperature cur\'e will approximate the seasonal 

 air-temperature curves except that the amplitude of the sea bottom 

 temperature changes will be smaller and the peaks and troughs will be 



