198 University of California Publications in Zoology [Vol. 18 



latitude and, to some extent, according to longitude. The highest 

 temperature of the surface waters of the ocean, as one may naturally 

 expect, is in the lowest latitudes on both sides of the equator, where the 

 intensity of the solar radiation reaches its maximum. With an 

 increase in distance from the equator toward the poles there is a grad- 

 ual decrease in temperature. The difference in temperature is here 

 about 28° to 29°C, ranging from 28?5C near the equator to 1?4C at 

 latitude 60" (see table 6) or to 0° in the North Polar Basin at about 

 80° latitude. Again, a difference in surface temperature prevails 

 between the surface waters of the coastal region and those of the mid- 

 Pacific, and as a general rule the temperature of the surface water 

 rises with the increase in distance from the Californian coast toward 

 the mid-Pacific. But in the mid-Pacific, as well as near the coast, the 

 temperature gradually decreases with the increase in distance from 

 the equator toward the poles. The temperature near the shores, how- 

 ever, is more subject to fluctuations due to various causes. Thorade 

 (1912) has shown in detail the variations in temperature off the coast 

 of California with isotherms for surface temperatures for each month 

 of the year. Certain "cold islands" surrounded by warmer waters, 

 off Seattle and San Francisco, disappear entirely during some months 

 but are very prominent in others, the appearance and disappearance 

 of these * ' cold islands ' ' being caused by the seasonal changes in winds 

 with their influence upon the waters. The shifting of the isothermal 

 lines near the shores is also conspicuously noticeable in the varying 

 seasons. Upwelling of the cold bottom waters is the cause of cold 

 belts along the coast of California (Holway, 1905). An instance of 

 narrow cold water belt is found in the waters along Cape Mendocino. 

 Some limited areas of shallow water near the coast have higher tem- 

 perature than the surrounding deeper waters. All these complexities 

 help to diversify the thermal conditions of the surface waters, but 

 on the whole the temperature decreases with the increase of distance 

 from the equator to the poles (table 6). 



In the Arctic Ocean the surface temperature is nearly like the 

 bottom temperature, varying from 1?80C in April to 0?80C in 

 August. The temperature in the different depths in that region varies 

 from 0?30 to 0?80C (Nansen, 1902) being also uniform in that 

 region. This, however, is not true in the lower latitudes, where the 

 temperature varies with the various depths, decreasing gradually 

 with the increase in depth until in the greatest depth a minimum tem- 

 perature is reached which is nearly identical with that of the Arctic 

 waters. 



