WATER MASSES AND CURRENTS OF THE OCEANS 189 



through the Strait of Bab-el-Mandeb. According to Vercelli and 

 Thompson, this exchange is subject to a distinct annual variation that is 

 related to the change in the direction of the prevailing winds in winter 

 and summer. In winter, when south-southeast winds blow in through 

 the Strait of Bab-el-Mandeb, the surface layers are carried from the 

 Gulf of Aden into the Red Sea, and at greater depths highly saline Red 

 Sea Water flows out across the sill. In summer, when north-northwest 

 winds prevail, the surface flow is directed out of the Red Sea, and at some 

 intermediate depth water having a lower salinity and a lower tempera- 

 ture than the outflowing surface water flows in from the Gulf of Aden. 

 At still greater depths, highly saline Red Sea Water appears to flow out 

 over the sill, but it is probable that this outflow is much less than the 

 outflow in winter. On the basis of direct measurements of currents at 

 anchor stations, Vercelli found that in winter the average inflow amounts 

 to approximately 0.58 million m^/sec, whereas the outflow of Red Sea 

 water amounts to approximately 0.48 million m^/sec. No measurements 

 are available for summer, but it is estimated that the average annual 

 outflow is between 0.3 and 0.4 million m^/sec — that is, approximately 

 one sixth of the amount that flows out through the Strait of Gibraltar. 

 This conclusion is in agreement with the fact that the Red Sea Water is of 

 less importance in the Indian Ocean than the Mediterranean Water is in 

 the Atlantic Ocean. 



Currents of the South Pacific Ocean 



The only major current of the South Pacific Ocean that has been 

 examined to some extent is the Peru Current. In accordance with the 

 nomenclature proposed by Gunther, the name "Peru Current" will be 

 applied to the entire current between the South American Continent and 

 the region of transition toward the eastern South Pacific Central region. 

 The part of the current which is close to the coast will be called the Peru 

 Coastal Current, whereas the part which is found at greater distances will 

 be called the Peru Oceanic Current. 



The origin of the Peru Current has to be sought in the subantarctic 

 region, where part of the Subantarctic Water that flows toward the east 

 across the Pacific Ocean is deflected toward the north when it approaches 

 the American Continent. The total volume of water of the current does 

 not appear to be very great. On the basis of a few Discovery stations, it is 

 found that the transport lies somewhere between 10 and 15 million m^/sec, 

 and this figure includes transport of the upper water layers and of 

 Antarctic Intermediate Water. The western limit of the current appears 

 to be diffuse and cannot be well established on the basis of the available 

 data, but it is probable that the current extends to about 900 km from 

 the coast in 35°S. The northern limits, according to Schott, can be 

 placed a little south of the Equator, where the flow turns toward the west. 



