Ocean Temperatures along the West Coast of North America. 251 



40, there being warmer water both to the north and to the south of 

 this region. But a cold current flowing down from Alaska would 

 continually rise in temperature as it moved southward. The only re- 

 maining explanation is that there is a belt of cold water upwelling 

 from the adjacent ocean depths. 



The above surface temperature relations present two problems. 

 First, what is the cause of this cold-water belt? We have already 

 seen that it must be due to an upwelling from the adjacent ocean 

 depths, but what is the cause of this upwelling? And secondly, why 

 should the coldest portion of this area be in the vicinity of Cape Men- 

 docino, instead of farther north? 



An drees (10) attributed the cold-water areas to a vertical current 

 caused by the winds blowing off shore and driving the surface water 

 to the leeward, thus causing a return drift at the bottom of the ocean 

 and an upwelling near shore. Hann (11) accepted this view and added 

 4 'the sharp deflection of an ocecan current off shore may cause a rise 

 of cold water from below". He also assumed that the whole coast of 

 California belonged to the area of the constant trade winds. Buchanan 

 also accepted the theory of Andre es. But observations show that the 

 trade-wind region does not extend as far north as California and the 

 component of the wind velocity normal to the coast blows toward the 

 land except for a few weeks in the winter time, the season when the 

 temperature is nearest to the normal. 



Another peculiar fact concerning the temperature distribution is 

 shown by the charts made by Sir John Murray (12). They indicate 

 that water temperatures over the continental shelf are notably less 

 than those at the same level but farther out over the great ocean 

 depths. 



The observations and hypotheses referring to the relatively cold 

 water lying along the west coast of North America may, according to 

 Holway, be summarised as follows: 



a) 1 ) The definite belt of cold water can not be traced south of 

 Point Conception. 



b) In the summer, the coldest part of this belt is in the vincinity 

 of Cape Mendocino. 



c) The source of this cold coast water is in the ocean depths to 

 the northwest of Cape Mendocino. 



J ) The observations a) and b) and the theory of Zoppritz have an important 

 bearing on the hypotheses c) and d). 



