32 



OCEANOGRAPHY: 



tion, bend this current north in the Northern Hemis- 

 phere and south in the Southern Hemisphere. Con- 

 tinental barriers further serve this bending into a 

 clockwise northern and counterclockwise southern 

 rotation of waters, or current patterns that match 

 those of the winds. Various modifications of the 

 primary ocean-current pattern occur as secondary 

 currents. The modifications are caused by any com- 

 bination of the secondary current-producing factors. 



The other primary current-producing factor, 

 changing water density, is most important in creating 

 vertical and deep-sea currents. These changes in 

 density are caused by variations in the temperature 

 and/or salinity of water; either decrease in tempera- 

 ture or increase in salinity causes water to become 

 denser or heavier. Because there is a tendency for 

 temperature and salinity variations between adjacent 

 waters to be made homogeneous by water move- 

 ments, currents are the means by which the dif- 

 ferences are equalized. In general, such tempera- 

 ture-salinity variations also contribute to local 

 currents as well as to the pattern of deep-sea currents. 



The main pattern of the deep-sea currents is easiest 

 to trace in the Atlantic Ocean. To the south, the cold 

 Antarctic waters are deep because they are denser 

 and heavier than the overlying waters. They move 

 northward at a rate approaching 1 mile an hour. A 

 pattern of like, but southward, movement occurs in 

 the deep Arctic waters. However, the deepest and 

 coldest Arctic waters are interrupted by an east- 

 west submarine ridge near the Arctic Circle. This 

 ridge allows the warmer, but cool, higher Arctic 

 water layers to continue southward. Eventually, 

 these southward-moving, cool Arctic waters meet 

 northward-moving, warmer waters off Greenland and 

 Laborador. The meeting of the two currents, be- 

 cause of their temperature and salinity differences 

 results in a definite pattern of underwater currents. 

 The northward-moving warmer waters are dense, 

 mostly from a high salt content; the Arctic waters, 

 from low temperature. When the two masses con- 

 tact, they produce a mixture that is saltier than the 

 Arctic and cooler than the warmer waters. This mix- 

 ture is denser than either of its components, so it 

 sinks to form the North Atlantic Deep Water, a cur- 

 rent that moves southward. North of the equator, the 

 North Atlantic meets the colder and denser Ant- 

 arctic Deep Water. Finally, the Antarctic waters 

 force their way beneath the North Atlantic. 



DEEP-WATER UPWELLING 



There is a general belief that ocean winds affect 

 deep-water upwelling, and that this phenomenon, in 

 turn, is responsible for surface temperatures and 

 coastal fogs along the Pacific Coast of North America 

 and elsewhere. The hypothesis is as follows; The 

 action of wind parts the ocean surface waters, creat- 

 ing an area that must be filled by other waters. 

 However, the filling is not from the surface. Rather, 

 it is by the upwelling of deep, cold water; which 

 mixes with warmer water at the surface (Figure 3.4). 



Figure 3.4 Production of offshore fog belts. Sucti things as ocean 

 winds con part ocean surface waters ond lead to upwelling of the deep 

 cold waters which coot and condense surface winds. 



This upwelling is thought to be of rather regular 

 seasonal occurrence near the shore. During part of 

 the year winds pass over areas of colder water. The 

 cold water cools the air, causing water vapor con- 

 densation in the form of offshore or coastal fog. This 

 cycle contributes to the Fog Belt climate of the Pa- 

 cific Coast States and causes coastal temperature 

 differences in locales fairly close to one another. 



In the last few years waters of the eastern Pacific 

 Ocean have gradually become warmer. This phe- 

 nomenon could be explained on the basis of a reduc- 

 tion of ocean winds, hence, of deep-water upwelling. 

 In other words, the quieting of winds could reduce 

 the amount of cold water upwelling, and the resultant 

 cooling of surface waters. 



Another cause of deep-water upwelling is surface 



