the eastward-flowing Monsoon Current. The result is that, together 

 with the Equatorial Countercurrent, all the currents in the Indian 

 Ocean north of lat. 2°S. have a strong easterly trend. With the 

 reversal of the monsoon during the Northern Hemisphere winter, 

 the northeast monsoon reinforces the westward-flowing North 

 Equatorial Current. The picture, then, is similar to that in the 

 Pacific Ocean, with an easterly Equatorial Countercurrent sand- 

 wiched between the westerly North and South Equatorial currents. 



In the Southern Ocean the west wind drift causes a great and 

 continuous eastward-flowing current encircling Antarctica. 



Over most of the ocean surface the currents are fairly weak, 

 with speeds of around half a knot. However, in the more clearly 

 defined currents, such as the equatorial system of ocean currents, 

 speeds may reach one or two knots ; and in the strongest currents, 

 such as the Gulf Stream, speeds as high as four or five knots may 

 be found. Most of the surface currents are not very deep ; except in 

 the case of the strongest ones, their strength has almost disap- 

 peared at a depth of a few hundred feet. The Gulf Stream's high 

 speeds are not found much deeper than 1 200 feet. 



The weaker currents often vary their direction because they may 

 be radically changed by local weather. Yet even within the stronger 

 currents we find variety; fast-moving, narrow streaks alternating 

 with weaker countercurrents produce quite a different picture from 

 the broad, average currents shown on the charts. So a sailor may 

 often find himself in a current that is far from constant, either in 

 direction or speed, but in the long run he will gain by making use 

 of the average current shown on the charts. 



Perhaps the most important consequence of ocean currents is 

 their effect on climate. Because the currents carry great masses of 

 water from one place to another, large quantities of heat and cold 

 are transported from one latitude to another. The harbors along 

 the coast of Norway are free from ice because of the flow of rela- 

 tively warm Atlantic water into the Norwegian Sea. Yet the harbors 

 on the coast of Labrador - located farther south than Norway - do 

 not benefit from such a flow of warm water and are consequently 

 frozen for many months of the year. However, the popular notion 

 of the Gulf Stream as a river of warm water flowing toward the 

 western coast of Europe is incorrect. We should regard the Gulf 

 Stream as a boundary current between the warm, blue waters of 

 the Sargasso Sea in the central North Atlantic and the cold, green 

 waters to the north and northwest. Because of its rapid flow, the 

 Gulf Stream prevents the Ughter, warm water from spreading out 

 over the denser cold water. 



What climatic changes would be brought about if the Gulf 

 Stream became stronger or weaker? If it weakened, the climate of 

 Europe would possibly become warmer, because the warm Sargasso 

 Sea water would be less confined and would be free to spread 

 farther north and east. But we have too little knowledge to answer 

 such questions about the relationship between the changes of cur- 

 rents and changes of climate. The interactions of ocean and atmos- 

 phere are so complex that any attempts at prediction seem purely 

 speculative. 



The cold water to the northwest of the Gulf Stream is brought 

 south by the Labrador Current, and with it comes a march of 

 icebergs which cause such a notorious hazard to ships off' the Grand 



^ 



Hundreds of icebergs, some more than two 

 hundred yards long, are brought south from 

 Baffin Bay by the Labrador Current. They 

 are carried into the North Atlantic, where 

 they are a menace in shipping lanes. 



The chart on page 208 shows the salt 

 content of Atlantic Ocean water above a 

 depth of 1250 meters (684 fathoms). The 

 lines are isohalines (lines of equal 

 salinity) , expressed in parts per thousand. 

 The cold but less saline Antarctic 

 Intermediate Water spreading northward 

 sinks from the surface at about lat. 50° S., 

 and is shown on this chart extending 

 northward from about lat. 45° S. This body 

 of water lies above the more saline 

 southward-flowing North Atlantic Deep 

 Water, which sinks past this depth in the 

 extreme North Atlantic and rises again to 

 this depth in the extreme South Atlantic. 

 Highly saline Mediterranean water spreads 

 westward and northward at this intermediate 

 depth. (This chart is taken from the atlas 

 of the Meteor Expedition of 1926-27.) 



207 



