THE PACIFIC OCEAN 



109 



appears to be stronger and more regularly developed than 

 the corresponding current in the Southern Hemisphere. 

 The former current must also be regarded as a forced 

 current which is maintained partly by the prevailing 

 winds and partly by the factors driving the easterly cur- 

 rent of the northern part of the ocean, namely, the dif- 

 ferences in density between the subtropical and the sub- 

 arctic water. Since the North Pacific is limited on the 

 north, the entire mass of water which is carried toward 

 the east in the North Pacific must return, whereas in 

 the South Pacific a considerable part of the water con- 

 tinues eastward to the south of South America. This 

 circumstance perhaps explains the more conspicuous 

 development of the westerly tropical current in the 

 North Pacific. 



Off the coast of Japan, in the latitude of Yokohama 

 and to the north of this latitude, we find very complicated 

 currents. No lines have been drawn, but by means of the 

 numerical values on the chart, one easily recognizes the 

 line of demarcation, representing the boundary between 

 the warm water to the south and the cold water to the 

 north, which was seen in Section IX. A warm current, 

 theKuroshio, can be traced as a narrow and very strong 

 current which follows the southeast coast of Japan to ap- 

 proximately latitude 37° north. Here it meets the cold 

 current coming from the northeast, the Kurile (Oyashio) 

 Current. Both currents bend toward the east, the Kuro- 

 shio partly to the south and the Kurile Current partly to 

 the north. Along the border of the two currents a suc- 

 cession of whirls is apparently developed and it is prob- 

 able that future observations will show that these whirls 

 develop at various places along the line of demarcation 

 and reach varying intensities. The observations of the 

 Carnegie indicate the major features of the current sys- 

 tem but cannot be used for a discussion of the details. 

 We remind the reader that a corresponding region with 

 great contrasts is found in the North Atlantic to the south 

 of the Grand Banks, and that corresponding whirls un- 

 doubtedly are developed there. 



The whole of the North Pacific to the north of lati- 

 tude 30° north is dominated by the easterly current, 

 which in the southern part carries warm water of high 

 salinity, and in the northern part carries cold water of 

 low salinity. Because of the difference in temperature, 

 the density is increasing toward the north. The observa- 

 tions of the Carnegie cannot disclose any details as to 

 this current, but they show that it is strongly developed 

 to a depth of more than 500 meters. The inclination of 

 the isobaric surfaces toward the north in the North Pa- 

 cific is the dominating feature in the topography of the 

 surfaces. 



The easterly current of the North Pacific divides 

 into two branches when it strikes the coast of North 

 America. The northern branch turns toward the north 

 and bends into the Gulf of Alaska and returns toward the 

 west on the southern side of the Aleutian Islands. This 

 branch is shown in the British Admiralty Charts and in 

 the chart by Merz, and appears in our charts, thanks to 

 the observations made in the Gulf of Alaska by the United 

 States Bureau of Fisheries. 



The other and more important branch of the easterly 

 current of the North Pacific bends toward the south. The 

 form of the North American coast is probably of great 

 importance to the turning of the current, and to the fact 

 that the southerly current along the coast runs with a 

 very high velocity off the coast of California where it is 



known as the California Current. As in the case of the 

 Peruvian Current, the increase of density toward the 

 coast cannot be ascribed to an upwelling of deep water, 

 but is dynamically conditioned. The California Current, 

 as it appears on our dynamic maps, is maintained by the 

 difference of density between the subtropical and sub- 

 arctic regions, but the increase in density toward the 

 coast is a direct result of the existence of the current. 



An upwelling takes place in the upper layers because 

 of the transport of water away from the shore by pre- 

 vailing winds. Thorade (1909) has shown that this trans- 

 port and, consequently, the upwelling is subjected to 

 considerable seasonal change. As to the character of 

 the upwelling and the relation of this phenomenon to the 

 low temperatures at greater depths, we refer to our 

 discussion of the Peruvian Current. In this place it 

 should again be emphasized that according to our con- 

 ception the low surface temperatures are the result of 

 an upwelling of water from small depths, whereas the 

 low temperatures at greater depths have nothing to do 

 with the upwelling, but are associated with the presence 

 of a southerly current along the coast. 



The rapid heating of the surface, which takes place 

 in this southerly latitude, must lead to the development 

 of a thin surface layer of relatively high temperature. 

 The transition from this surface layer to the underlying 

 water takes place in a short distance, and convective 

 currents therefore cannot penetrate to any great depth. 

 The velocity of the California Current decreases with 

 increasing depth and at a depth of 400 meters the cur- 

 rent is very weak. 



In the regions between the coast of California and the 

 Hawaiian Islands the currents are rather irregular. At 

 the most northern stations we find, on the whole, an east- 

 erly current and at the most southern stations a wester- 

 ly current, and between the Islands and the American 

 coast the water flows mainly from the north. From the 

 appearance of sections VII and XV, and from the curves 

 showing the vertical distribution of temperature and sa- 

 linity at stations 139 to 146, it appears as if a transport 

 of water toward the north takes place in the upper layers 

 at stations 142 to 146. The dynamic charts do not indi- 

 cate such a transport, which perhaps must be attributed 

 to the effect of the wind. Below a level of 200 or 300 

 meters the transport appears to take place principally 

 from the west. 



At the stations in the immediate vicinity of the Ha- 

 waiian Islands we find a rather strong surface current 

 from the east which, however, decreases rapidly in ve- 

 locity with ircreasing depth. The water of high salinity, 

 which is foi-.nd below the surface at stations 139 and 140, 

 appears to come from the region of high salinity to the 

 west. 



The Equatorial Countercurrent is especially well de- 

 developed in the Pacific. As a rule it is a little to the 

 north of the equator, running with high velocity toward 

 the east. It is probable that this current is extended 

 across the whole width of the Pacific Ocean but it is un- 

 doubtedly subjected to considerable variations, partly of 

 seasonal character and partly owing to circumstances of 

 which we have no knowledge. It is generally assumed 

 (Defant, 1928; Krflmmel, 1911) that the Equatorial 

 Countercurrent represents a compensation current car- 

 rying back again to the east part of the water which is 

 transported toward the west by the trade-wind currents. 

 Furthermore, it is assumed that this countercurrent, 



