78 



DISTRIBUTION OF SALINITY, TEMPERATURE, DENSITY 



greater in the North Atlantic and the North Pacific Oceans than in the 

 southern oceans. In the second place, they show that in the southern 

 oceans the temperature range is definitely related to the range in radiation 

 income, whereas in the northern oceans no such definite relation appears 

 to exist. The great ranges in the northern oceans are associated with the 

 character of the prevailing winds and, particular^, with the fact that cold 

 winds blow from the continents toward the ocean and greatly reduce the 

 winter temperatures. Near the Equator a semiannual variation is 

 present, corresponding to the semiannual period of radiation income, but 

 in middle and higher latitudes the annual period dominates. 



Annual Variation of Temperature in the Surface Layers. At 

 subsurface depths the variation of temperature depends upon four fac- 



Fig. 17. A. Annual variation of temperature at different depths in Monterey 

 Bay, California. B. Annual variation of temperature at different depths in the 

 Kuroshio off the south coast of Japan. 



tors: (1) variation of the amount of heat that is directly absorbed at 

 different depths, (2) the effect of heat conduction, (3) variation in the 

 currents related to lateral displacement of water masses, and (4) the effect 

 of vertical motion. The annual variation of temperature of subsurface 

 depths cannot be dealt with in a general manner, owing to lack of data, 

 but it is again possible to point out some outstanding characteristics, 

 using two examples from the Pacific and one from the Atlantic Oceans. 

 The effects of all four of the important factors are illustrated in fig. 17 A, 

 which shows the annual variation of temperature at the surface and at 

 depths of 25, 50, and 100 m at Monterey Bay, California, according to 

 Skogsberg. Skogsberg divides the year into three periods: the period of. 

 the Davidson Current, lasting from the middle of November to the 

 middle of February, the period of upwelling, between the middle of 

 February and the end of July, and the oceanic period, from the end of 

 July to the middle of November. The California Current off Monterey 

 Bay, during the greater part of the year, is directed to the south, but dur- 



